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- CSIRO Publishing
10.1071/PVv2010n147p47
ABSTRACTS
SECTION 3
ABSTRACTS
ASEG-PESA 2010 Conference Handbook
AUGUST 2010
PREVIEW
47
Abstracts
Day 1: Monday 23 August 2010
8:45–10:15
Opening Ceremony, Plenary Session
and Society Awards
PLENARY SPEAKERS
Dr Chris Pigram
Chief Executive Officer, Geoscience Australia
the area of operational step-change innovation. The decision
resulted from a combination of the following views:
• Several emerging economies with very large populations
were about to enter a phase of growth typically associated
with high rates of mineral and metal demand.
• The orebodies of the near future were likely to be of lower
grades, further from infrastructure, and deeper.
In response to this strategic shift, Rio Tinto Innovation (RTI)
was formed ‘to help enable Rio Tinto’s business units to do
tomorrow what they cannot do today’. The division is focusing
its efforts on a modest number of step-change technologies in
the areas of surface mining, underground mining, mineral
recovery and orebody discovery/knowledge.
ABSTRACTS
In the field of surface mining, RTI is focused on delivering the
Mine of the FutureTM, a highly automated system of mining
hardware and software working to significantly improve the
real time knowledge of the orebody, and the reliability and
predictability of mining operations, to maximise value creation.
Efforts in the field of underground mining have been focused on
designing large machines capable of boring shafts and tunnels at
significantly higher rates than current best practice. If successful
these machines will facilitate a compression of project timelines,
with large value resulting from more immediate delivery of
saleable products.
Dr Chris Pigram is the Chief Executive Officer of Geoscience
Australia. He has over 30 years experience in Southeast Asia,
the West Pacific and Australia in a wide range of geological
research and mapping. He has authored or co-authored over
90 publications covering tectonics, petroleum, basin analysis
and marine geoscience.
RIO TINTO AND STEP-CHANGE
INNOVATION – DRIVERS AND PROGRESS
In the field of mineral recovery, we have several projects
aimed at upgrading ores or improving processing recoveries.
If successful these technologies could convert current waste
material to saleable ores, significantly reduce the size and cost
of downstream processing plants, or make low grade orebodies
economic.
With respect to orebody discovery, Rio Tinto continues to work
with UWA on the development of a highly sensitive airborne
gravity gradiometer. If successful, the project will deliver a
commercial instrument with a sensitivity of 1 Eotvos. Good
progress on this exciting project has been made in the past
12 months.
Jon McGagh
Head of Innovation, Rio Tinto
11:00–12:30
Day 1 Session 2 Stream 1
MINERALS DISCOVERY
MODELLING IRONSTONES USING MAGNETIC DIPOLES
Roger Clifton
Northern Territory Geological Survey, Darwin, NT, Australia
[email protected]
John McGagh has been with Rio Tinto since 1980, most recently
as Global Head of Procurement looking at goods and services
purchased by Rio, and now as the Head of Innovation which
also covers research and development within the company. His
background has spanned e-marketplaces to inbound supply
chains, as well as project engineering and operations.
At the commencement of the 21st century, Rio Tinto made a
deliberate strategic decision to significantly increase its efforts in
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Using an elemental dipole as the finite element, power spectrum
modelling of IOCGU targets is demonstrated on Tennant Creek.
Many of the abandoned goldmines on Tennant Creek are
successfully discovered using the magnetic data alone, and the
depths to the ironstone targets reasonably accurately estimated.
The implication for IOCGU targets elsewhere is significant.
The increase of magnetic intensity at the surface allows an
immediate challenge to the technique because the signature
requires the highest frequencies. However the depth is known
precisely. In this case, it is possible to stack large areas of data
ASEG-PESA 2010 Conference Handbook
to obtain the frequency dependence of this target. Using the
assessed frequency dependence, the filter which had been
applied at the time of acquisition can be estimated and reversed.
Arguable success is achieved.
Mapping the surface of a buried basalt flow is also attempted.
Very noisy results are achieved. However the modest successes
achieved indicate further effort will be rewarded.
FLYING DOCTOR CASE HISTORY
Kate Godber1*, James Reid2, John Bishop3 and Ted Tyne3
Pty Ltd, South Brisbane, QLD, Australia
2Groundprobe, Malaga, WA, Australia
3PIRSA, SA, Australia
1Geoforce
[email protected]
The Flying Doctor Deposit, located approximately 8 km east of
Broken Hill in western NSW, has long been used as a test site
for geophysical techniques and was part of the coverage of the
first potential field surveys carried out there in the late 1940s.
From the 1960s through to the present, most geophysical
techniques were tried over the deposit. The first test survey was
actually the ‘discovery’ survey: Flying Doctor showed up as a
very strong frequency domain response in the 1960 McPhar IP
survey. This was followed by various incarnations of ground
electromagnetics (EM), ground IP, gravity, magnetics, downhole
EM, magneto-metric resistivity (MMR), downhole MMR,
sub-audio magnetics (SAM), fixed-wing EM, and most recently
helicopter EM (SkyTEM) in August 2009. The Flying Doctor
deposit is blind (depth to top >50 m below surface), size <1.5 Mt
at 15% Pb+Zn, and is composed of several elongate, steeply
northwest dipping plates. The mining lease owner, Perilya, has
recently recommenced the drilling campaign with a view to
mining and the long standing test site is now at risk of
disappearing.
This paper summarises the results of the Flying Doctor
geophysical surveys, compares the data from old versus new
geophysical techniques, and presents an outline of the evolution
of geophysics in Australia from the unique perspective of this
one prospect.
The results highlight the improvement in electrical and
particularly electromagnetic techniques and show the much
better ability of the most recent methods to penetrate deeper and
discriminate ore from cultural noise and unwanted background
responses.
DISCOVERY CASE HISTORY OF THE MORAN
MASSIVE NICKEL SULPHIDE DEPOSIT, KAMBALDA,
WESTERN AUSTRALIA
David M. Johnson1*, Somealy Sheppard2, Jacob Paggi1
and John Coggon3
1Independence Group NL, Belmont, WA, Australia
2Lightning Nickel Pty Ltd, Belmont, WA, Australia
3Mines Geophysical Services Pty Ltd, Belmont, WA, Australia
[email protected]
The Moran deposit was discovered in September 2008 when
underground diamond drill-hole LSU-152 intersected a 12.3 m
thick zone of disseminated, matrix-textured and massive
pyrrhotite-pentlandite-chalcopyrite mineralisation with an
average grade of 6.0% nickel. An initial indicated and inferred
ASEG-PESA 2010 Conference Handbook
resource estimate of 456 000 tonnes grading 7.1% Ni for 32 400
tonnes contained nickel metal was announced to the Australian
Securities Exchange on 28th July 2009. Moran is located within
the Kambalda nickel sulphide camp within the NorsemanWiluna Greenstone Belt of the Yilgarn Craton, Western
Australia. Nickel deposits in the camp are hosted by the basal
komatiite Silver Lake Member of the Kambalda Formation,
which overlies the Lunnon Basalt. Nickel is contained within a
sulphide mineral assemblage dominated by pyrrhotite, which is
a strong conductor. The discovery drill hole was designed to test
a conductor interpreted from down-hole transient electromagnetic
(DHTEM) data recorded in several diamond drill holes
collared in the nearby underground mine workings of the McLeay
and Victor South orebodies. The DHTEM survey was read
using an underground transmitter loop constructed by passing
wire through two declines, one ventilation shaft and an
underground drill hole. Interpretation of the data was carried out
using rectangular multiple current ribbon modeling software.
The discovery of Moran represents the culmination of five years
of exploration by Independence Group NL within the interpreted
southern extension of the komatiite lava channel hosting the
Long nickel orebody. Interpretation of the geophysical data was
technically straightforward. However, the interpreted geological
setting of the conductor models, assessed within the context of
the genetic model for Kambalda-style nickel mineralization,
proved critical to identifying the potential economic significance
of the target.
Day 1 Session 2 Stream 2
TECHNOLOGY ADVANCES
A SYSTEMATIC APPROACH TO THE EVALUATION
OF THE QUALITY OF TIME DOMAIN AEM DATA
Yvonne Wallace
Barrick Gold, WA, Australia
[email protected]
A recent airborne electromagnetic (EM) survey in Papua New
Guinea (PNG) has provided an opportunity to trial systematic
measures of data quality in a similar manner to those routinely
employed in airborne magnetic and radiometric surveys. These
calibration checks are designed to demonstrate the integrity of
the acquisition system from a client perspective.
AeroTEM IV data were acquired over two project areas in PNG
during 2008/09, and two sets of check flights were acquired
over pre-determined test lines. These were (a) pre-survey check
flights and (b) repeat survey check flights. Pre-survey check
flights consisted of a range of helicopter and bird manoeuvres
carried out along line to assess system performance under
varying survey conditions. These manoeuvres included: normal
survey-type flight, bird swing left to right/right to left, speed
increase/decrease, climb/descend, and at altitude with Tx on and
off. Repeat survey check flights consisted of flying along the
same line prior to each flight at survey height and at altitude.
The 45 check lines acquired during the survey are used to
demonstrate the amplitude of noise due to aircraft manoeuvre,
and the pre-flight detection of system error using repeat data.
Recommendations are made for evaluation of data quality
consisting of the pre-survey and repeat survey check flights
listed above, plus a heading check. Spectral fast fourier
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ABSTRACTS
Abstracts
Abstracts
transform (FFT) plots can be usefully employed to identify
unwanted noise and source. Inversion of one or more lines of
data from each flight is recommended to check the geologic
value of the data.
EVOLUTION OF VTEM – TECHNICAL SOLUTIONS
FOR EFFECTIVE EXPLORATION
Jean Legault1*, A. Prikhodko1, A. Bagrianski1, P. Kuzmin2 and P. Tishin2
1Geotech Ltd., Aurora, Ontario, Canada
2Geo Equipment Manufacturing Ltd., Aurora, Ontario, Canada
[email protected]
ABSTRACTS
The helicopter-borne Versatile Time Domain Electromagnetic
System (VTEM) is a geophysical instrument which has been
in continuous development, utilizing most recent advances in
digital electronics and signal processing for deeper penetration;
higher spatial resolution; better resistivity discrimination; and
increased detection of both weak and highly conductive targets.
Since its inception in 2002, more than 1 200 000 line kilometers
have been flown around the world, in widely diverse geological
environments and spanning a broad spectrum of exploration
tasks. The continuous technical development of the system is
firmly based on the combination of survey practice, new
electronic and schematic achievements, as well as requirements
of the mining industry. It stands firmly on the principle of
implementing the complex upgrades that contribute to improving
noise reduction, increasing dipole moment, waveform
optimization, increasing time-width of decay measurement,
and increasing precision of the data acquisition system.
Behind these technical improvements and design is the mineral
exploration industry’s constant demand for advances in depth
penetration, conductivity range, conductance discrimination,
spatial resolution, penetration ability through conductive
overburden. In the results to date VTEM surveys continue
to discern anomalies left undetected by previous airborne
EM surveys.
The evolution and possibilities of the system are demonstrated
using multiple survey tests, both new and previous, over known
mineral deposits and natural occurring geologic targets, and
quantified directly using modeling and depth imaging with
VTEM historical specifications for varying characteristics of
geological environment. Examples of these comparisons include
the Caber and other Matagami Lake volcanogenic massive
sulphide deposits in northern Quebec, the Eagle One magmatic
nickel deposit in northern Ontario, uraniferous graphitic
structures and targets of the Athabasca Basin northern
Saskatchewan, kimberlites and others.
maximizing the depth of exploration. Ongoing development
has produced the next generation of Digital AeroTEM HTEM
system which minimizes the dependence on analog components
while maintaining the key components of the AeroTEM system
(on-time, X-component, and early off-time data). The
transmitted waveform is defined and produced through on-board
digital signal processing (DSP) software with full control over
the waveform type, pulse width, and amplitude. The monitoring
and control is performed at a high rate (approximately 200 kHz),
which allows for precise conditioning of the turn-off. The
receiver electronics are controlled by the same DSP as the
transmitter which results in a well synchronized highly sampled
signal. This high rate digitization makes it possible to minimize
and/or remove the effects from high-frequency noise sources
(Gibbs effect, spherics, etc…) in real time or during postprocessing. Future research and development will focus on
active monitoring of the waveform to allow for compensation of
thermally-induced drift, waveform asymmetry and power supply
variations. The principal benefit of this development is in the
interpretability of the data. Data produced from a well-defined,
low-noise system will produce more accurate and ultimately
more useful, interpretations from the rigorous inversion codes
available today.
Day 1 Session 2 Stream 3
PROSPECTING WITH GRAVITY
THE PRESENT SITUATION AND DEVELOPMENT TREND
OF AIRBORNE GEOPHYSICAL TECHNIQUE IN CHINA
Sheng-qing Xiong
China Aero Geophysical Survey and Remote Sensing Center
for Land and Resources (AGRS), Beijing, China
[email protected]
The present situation of China’s airborne gravity and magnetic
survey technique and the gap between China and advanced
countries in this aspect have been summed up in this paper,
together with an analysis and prediction of the development
trend of airborne geophysical exploration in China.
[email protected]
The airborne geophysical exploration in China started in 1953.
Through more than fifty years’ development, the airborne survey
has gradually formed a complete technical system with China’s
own characteristics in such aspects as method and theory,
instrument development, system integration, data acquisition,
data processing, and data interpretation and application. This
system mainly includes various types of modified specialpurpose exploration airplanes (fixed-wing planes and
helicopters), airborne magnetometers and magnetic gradiometers
of varied models, real time digital magnetic disturbance
compensation system and high-precision navigational fixing
system and technology, advanced system integration technique,
flight survey technique (especially large-scale survey), and
whole set of special-purpose data-processing, interpretation
and mapping software system.
Since the inception of commercial helicopter time domain
electromagnetic (HTEM) systems in the late 1990’s, the
technologies that fill this space have matured and strengthened
to the point where HTEM dominates the field of airborne
electromagnetic surveying. Most of the development focus has
been on the strength of the transmitted signal with the goal of
In recent years, airborne gravity survey technique and gravity
gradient technique have developed very rapidly abroad,
accompanied by increasingly widespread application in the
world. In 2006, GT-1A airborne gravimeter was successfully
introduced from Russia in China. Through introduction,
digestion and assimilation as well as development of
THE CONCEPT AND DEVELOPMENT OF A TRULY
FLEXIBLE HTEM SYSTEM
Jonathan Rudd
Aeroquest Surveys, Mississauga, Ontario, Canada
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ASEG-PESA 2010 Conference Handbook
Abstracts
corresponding software and hardware, China has developed an
integrated airborne gravity and magnetic survey system with
advanced world levels and formed practical production
capability in a short period.
The high resolution airborne geophysical exploration technique
developed since the 1990s has further raised the precision of
airborne geophysical exploration and improved its capacity
for solving geological problems.
Salt bodies and 4-way structural closures are unique in that their
3D shape and near homogenous density present themselves as
ideal hydrocarbon trapping environments. An added complexity
occurs where these bodies exist in both onshore and transition
zone settings as deployment of conventional geophysical
methods such as seismic becomes cost prohibitive. The arrival
of Airborne Gravity surveying capabilities in recent years now
makes exploring such exploration play models viable.
In general, China’s airborne geophysical exploration technique
does not fall considerably behind advanced world levels, and has
the production capability of covering China’s whole territory
from seas and oceans to plateau.
Air-FTG® offers a high precision, high accuracy technology
that determines changes to the gravity field as sourced by
sub-surface geology. The technology is ideal for mapping
density contrasts due to structural faulting and or the presence
of geological bodies of near uniform density as exhibited
by salt and 4-way structural closures.
REQUIREMENTS FOR AIRBORNE GRAVITY GRADIENT
TERRAIN CORRECTIONS
This paper will present data examples demonstrating the
usefulness of FTG Gravity when investigating the prospectivity
of exploration play models.
Mark Dransfield
Fugro Airborne Surveys, WA, Australia
Accurate terrain corrections are important for all gravity
surveying. In airborne surveys, a digital model of the terrain is
constructed and terrain corrections are calculated at each
airborne measurement point. Airborne gravity gradiometry is
of high spatial resolution and is particularly sensitive to nearby
topographic variations, placing particular requirements on the
terrain corrections. A combination of mathematical analysis and
simulation studies has led to quantification of the requirements:
current on-shore, low-level gradiometer surveys require submetre accuracy in navigation and in digital terrain model
heights; cell sizes (and therefore also topographic sampling)
in the terrain model should be about one-third of the ground
clearance. The choice of terrain correction density depends
on the application and it is important that the interpreter of the
corrected gravity data has the ability to test the impact of
changes in this density.
Accurate calculation of the gravity gradient field at the airborne
sampling points may be achieved by a wide variety of either
spatial or harmonic domain methods. Calculation in the
harmonic domain is fast but assume the data represent a periodic
function on a planar surface. Padding methods for periodic
extension and piecewise continuation away from a plane both
add error and slow the calculation. Spatial domain methods are
slower but can be sped up by the use of various approximations.
In both cases, a clear understanding of accuracy requirements is
essential for making an appropriate trade-off between accuracy
and speed.
FTG GRAVITY DATA FOR PROSPECTING
EXPLORATION PLAY MODELS
Colm A. Murphy* and Jade L. Dickinson
Bell Geospace Limited, Aberdeen, United Kingdom
[email protected]
Geophysical technologies are routinely deployed to investigate
and enhance exploration play models evoked to explain an
economic discovery’s geological setting. Such models are
diverse for different commodities, but two such models adopted
for hydrocarbon exploration lend themselves particularly suited
to gravity surveying methods.
ASEG-PESA 2010 Conference Handbook
Day 1 Session 2 Stream 4
PETROLEUM IN ONSHORE BASINS
ABSTRACTS
[email protected]
SEISMIC EXPLORATION IN DESERT AREA OF TARIM
BASIN
Jian Guo
Chinese Geophysical Society, China
[email protected], [email protected]
Tarim Basin is located in northwestern China and is the one of
main basins with abundant oil and gas. Due to existence of thick
low velocity-reducing layer in desert area, it is very difficult to
gain good seismic datum. The main problem in collecting data
include:
1) Bad shot and receiving situation cause very low signal-tonoise ratio and low resolution;
2) Undulant hypsography make complicated static correction;
3) Surface deep sand stratum induce absorption and attenuation
of seismic wave.
To finish the geologic target, we introduce following methods:
1) Enhancing analysis and investigation of surface structure to
perfect surface structure model which will serve for choosing
better shot points;
2) Calculating better static correction by surface refraction
tomography;
3) Exploding under water table to guarantee enough shot energy,
and embed the geophone to get the better receiving condition;
4) Selecting bigger diameter of dynamite to form better point
explosive response;
5) Surveying the noise wave to design the best acquisition
parameters;
6) Applying the compensation of absorbed energy of seismic
wave to gain better information.
After these methods are introduced, the signal-to-noise ratio
and resolution of main prospecting objective in collecting
seismic datum are improved obviously and obtain correct
geologic interpretation.
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Abstracts
THE PROPERTIES OF THE NEAR SURFACE LAYERS
AT NAYLOR FIELD, OTWAY, AUSTRALIA
Yousuf Al-Jabri*, Milovan Urosevic and Christian Dupuis
Curtin University of Technology & CO2CRC, Perth, WA, Australia
ABSTRACTS
[email protected]
A feature of the injection test site of Naylor Field is the
near-surface karst topography. In such geological terrain,
a change in water table level can influence the seismic response
and cause changes in the seismic wave scattering pattern.
High seismic repeatability is critical to the monitoring program
of the Naylor Field because of the small time-lapse effect related
to CO2 injection into a depleted gas reservoir (Naylor).
To understand the effect of changing ground conditions on
repeatability, we conducted so-called “microarray” investigation
of the near-surface layers at this site. Hence the aim of microarray measurements was to determine the properties of the near
surface layers during the wet and dry seasons. This could help
us understand and ultimately predict the seismic response and
hence survey repeatability at a given site. Measurements of
seismic response due to near surface property changes (seasonal)
could help optimise the design of time lapse surveys which
ultimately yields improved survey differencing. Measured elastic
properties of the near surface are used to produce seismic
response and predict repeatability as a function of the variable
soil conditions. In this study we investigated the variation of
elastic properties of both top soil and the deeper rugose claylimestone interface as a function of water depth level. Such tests
in fact simulate the measurements conducted in dry and wet
seasons and help evaluate the effect of these seasonal variations
on the seismic signature, which is then analysed in terms of
non-repeatability. In this study, we use both micro-borehole
(micro VSP) and micro-refraction arrays to analyse directional
properties of the near-surface.
SEISMIC SEQUENCE STRATIGRAPHY AND FACIES
ARCHITECTURE OF THE SCROPES RANGE FORMATION
IN THE BLANTYRE SUB-BASIN, DARLING BASIN, NSW
Mohamed Kh. Khalifa1 and Kingsley J. Mills2
1Geoscience & Petroleum Engineering Department, Universiti
Teknologi PETRONAS, Malaysia
2Geological Survey of NSW, Broken Hill, NSW, Australia
[email protected]
In this paper, we propose and present a seismic stratigraphic
interpretation, based on two-dimensional seismic data, of units
attributed to the Upper Cambrian to Middle Ordovician Scropes
Range Formation within the northwestern portion of the Blantyre
Sub-basin in the central part of the Palaeozoic Darling Basin,
western New South Wales. Data from only two shallow wells
of the 831 km² study area dealt with in this paper was available
to support the seismic investigations. Six seismic reflection
horizons are defined and used to separate five seismic sequences
named Units A, B, C, D and E. These features are identified in
three seismic lines and demonstrate the continuity of the Scropes
Range Formation throughout the northwestern part of Blantyre
Sub-basin. All seismic sequence boundaries are based on good
continuous markers, with strong amplitudes throughout the
study area. The acoustic basement beneath the Scropes Range
Formation, was almost certainly metamorphosed in the
Delamerian Orogeny (around 500 Ma) within the study area.
In addition, acoustic facies recognized in the three seismic lines
can be correlated with sedimentary facies observed in outcrop
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in the Scropes Range, 130 km west of the study area, and are
compared with acoustic facies in modern non-marine (fluvial)
sandstone units associated with local braided delta depositional
systems. The seismic facies identified from the seismic data
show features such as low-angle and high-angle clinoforms,
parallel and sub-parallel reflections and a few hummocky/wavy
reflections indicating shallow channel-fills and small-scale
fluvial channels. A combination of horizon mapping, seismic
facies analysis and seismic attribute mapping defines the
sequences. Complex geological features suggest many potential
structural and stratigraphic hydrocarbon traps. A high-resolution
seismic survey could lead to the definition of new exploration
plays in this underexplored region.
13:30–15:00
Day 1 Session 3 Stream 1
MINERALS DISCOVERY
EXPERIENCE WITH THE ISSUES OF SEISMIC
SURVEYING OVER BASALTS
Binzhong Zhou1, Peter Hatherly2, Troy Peters3 and Weijia Sun4
Earth Science and Resource Engineering
2Coalbed Geoscience Pty Ltd
3VelSeis Pty Ltd
4Institute of Geology and Geophysics, Chinese Academy
of Sciences
1CSIRO
[email protected]
In some of Australia’s underground coal mining areas, nearsurface basalt layers create problems for seismic reflection
surveying. Affected mines have less confidence in their
geological conditions and mine safety and productivity may
be compromised. In order to gain insights and obtain potential
solutions to this important problem, we have investigated
seismic reflection and borehole vertical seismic profiling data
from surveys at the North Goonyella Mine and the Moranbah
South coal mine lease, which are both located in the Bowen
Basin of Queensland.
At North Goonyella, seismic velocities determined from the
VSP survey indicate that the basalt is not fresh and up-going
reflections from layers below the basalt and clearly seen. For
the seismic reflection survey, advanced seismic data processing
techniques such as pre-stack depth migration were able to
improve the continuity of the coal seam reflections across the
zone affected by the basalt. No special acquisition parameters
were required.
At Moranbah South, the problem with the basalts proved to be
intractable. The basalts are hard and fresh, their total thickness
is up 40 m, their width reaches 360 m and unconsolidated
sediments lie between individual flows. The target coal seams
are at depths less than 310 m and neither long-offset data
acquisition nor prestack depth migration were able to produce
satisfactory results.
In general, the main issues for seismic surveying in basalt
covered areas are (i) the generation of complex down-going
and up-going wavefields which are due to the strong impedance
contrasts between the basalt and the surrounding strata,
and (ii) the generation of incoherent scattered waves from
inhomogeneities within the basalts and their rough margins. We
ASEG-PESA 2010 Conference Handbook
Abstracts
DEEP CRUSTAL SEISMIC SURVEYS FOR IDENTIFYING
PROSPECTIVE AREAS UNDER COVER
Ned Stolz
Geoscience Australia, Canberra, ACT, Australia
[email protected]
Geoscience Australia has been acquiring deep crustal reflection
seismic transects through-out Australia since the 1960s. The
results of these surveys have motivated major interpretations
of important geological regions, contributed to the development
of continental-scale geodynamic models, and improved
understanding about large-scale controls on mineral systems. In
2006 the Australian Government announced the Onshore Energy
Security Program which provided $59 million over five years to
fund pre-competitive data and science to reduce risk in energy
exploration. Under this program, Geoscience Australia has
collaborated with the state and territory governments and
AuScope (funded by the National Collaborative Research
Infrastructure Strategy) to acquire, process, and interpret over
5000 km of new seismic reflection data. These transects are
targeted over geological terrains in all mainland states which
have potential for hydrocarbons, uranium and geothermal
energy systems.
The first project was undertaken during 2006 and 2007 in the
Mt Isa and Georgetown regions of North Queensland.
Approximately 2300 km of seismic data were acquired,
processed, interpreted, and integrated with other geoscientific
information, including results of inversion of potential field data.
The final interpretations have identified several features of
interest to mineral and energy explorers; a previously unknown
basin with possible hydrocarbon and geothermal potential;
a favourable structural setting for orogenic gold deposits under
basin cover; and a favourable setting for iron oxide uraniumcopper-gold deposits. Other geophysical data were used to map
these features in 3D, particularly into areas under cover. Seismic
imaging of the full thickness of the crust provides essential,
fundamental data to economic geologists about why major
deposits occur where they do, and identify areas with the best
opportunities for future discoveries.
HYDROPHONE VSP IMAGING IN THE AGNEW –
WILUNA BELT, WESTERN AUSTRALIA
Andrew Greenwood1*, Milovan Urosevic1 and Anousha Hashemi2
1Curtin University of Technology, Bentley, WA, Australia
2BHP Billiton
[email protected]
A Vertical Seismic Profiling (VSP) experiment using a 24
channel hydrophone array was conducted concurrently with a
short 2D seismic section in the Agnew-Wiluna greenstone belt.
This greenstone belt is within the Yilgarn Craton and contains
over 100 km of continuous strike length komatiitic rocks which
host nickel-sulphide and other minerals. Complex structures with
steep dips, high angle faults, fractures and shears often control
the zones of mineralisation.
to having multiple active channels makes hydrophone VSP
imaging time efficient. The unique geometry of VSP surveys
offer favorable advantages over surface seismic particularly in
complex environments. Both shallow and steep dips can be
imaged as frequency content is preserved from the damaging
effects of irregular overburden.
The Agnew – Wiluna VSP field experiments produced high
quality signal to noise ratio images and high resolution seismic
images around the well for both near and far offset shots. Three
strike-slip faults crossing the sections were identified. Kirchhoff
migration of the VSP data imaged high angle structure with
detail. Apparent dips in the surface seismic and VSP are in
agreement with each other and appear to perfectly match foliation
alignments observed in numerous core samples. 3D structure in
the area maybe a limiting factor of any 2D survey here. Multidirectional or 3D VSP may resolve any outstanding issues.
Day 1 Session 3 Stream 2
TECHNOLOGY ADVANCES
FEASIBILITY OF IN-PHASE AIRBORNE TEM UTILISING
GRADIENT MEASUREMENTS
ABSTRACTS
have studied and confirmed these seismic phenomena through
computer modelling.
James B. Lee
Ti-Willa Technologies, New Lambton Heights, NSW, Australia
[email protected]
While electromagnetic surveys are sensitive to conductive
targets, it is well recognized that current technologies are not
effective in detecting very conductive “super-conductor”
targets. This is due to the response of these targets being
overwhelmingly in-phase, and so, not distinguishable in the
receiver from variations in the transmitted field due to changes
in the geometry of the system. Rigid systems can measure the
in-phase component, but are necessarily limited in the power
of the transmitter, while most TEM systems measure only the
out-of-phase or off-time signal.
The benefit of measuring the in-phase signal is quantified in
terms of the ratio of the in-phase to out-of-phase signal
magnitude, and increases in proportion to the square or cube of
the ratio of the target time constant to the on-time period of the
transmitter waveform. For highly conductive nickel sulfides
(for example) the benefit can be several orders of magnitude.
Measurement of the in-phase response requires subtraction of the
direct transmitter signal to a high level of accuracy. Dimensional
measurements are not viable for this. Measurement of gradients
of the EM field is explored as a means of differentiating the
direct transmitter field from the target signal. The foundation of
this proposal is that the gradients decrease more rapidly with
separation distance, than the field itself, and so are less (or
negligibly) influenced by the target.
The feasibility of this approach is demonstrated and quantified
in a simplified analytical model, and a more complete numerical
model. The models reveal the attainable performance of such a
survey system based on gradient measurements and implications
for its optimal design.
Hydrophones are broadband in frequency and extremely
sensitive to pressure waves. They do not require clamping to the
borehole wall making them highly deployable. This in addition
ASEG-PESA 2010 Conference Handbook
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Abstracts
FAST DIRECT RESISTIVITY TRANSFORMS
FOR TEM SYSTEMS
Aaron Davis1,2*, James Macnae1 and Kim Frankcombe3
1RMIT University, Melbourne, VIC, Australia
2Geoscience Australia, Canberra, ACT, Australia
3Southern Geoscience Consultants, Belmont, WA, Australia
[email protected]
ABSTRACTS
In 1987, Nekut published in Geophysics a method that used
the receding-image approximation of the time domain
electromagnetic (TEM) response of a concentric loop system
above a half-space to derive a simple, fast, direct transform that
calculates resistivity as a function of depth. This method is the
fastest of published transforms from TEM data to resistivity.
Following his example, we make a further simplification that
completely eliminates one intermediate step required by Nekut.
His intermediate step was used to resolve differences between
mirror depth (half the image depth) and the half-space diffusion
depth. We simply use the half-space diffusion depth directly in
Nekut’s receding image method without requiring a mirror-depth
calculation and a further calculation of its associated correction.
The result is an even faster direct resistivity transform method
that exactly matches the results of Nekut.
A further conceptual advance is immediately clear: the fast
direct resistivity transform can be expanded to other common
survey geometries such as coincident square- and circular-loop
TEM systems. This is achieved through use of the diffusion
depth with either direct forward modelling of the half-space or
the mirror approximation. We explore this conceptual advantage
and give an example of direct resistivity transforms for the
Slingram geometry commonly used in electromagnetic surveys.
DISRUPTED LAYERED LITHOLOGY CAN JEOPARDISE
AIRBORNE ELECTROMAGNETIC INTERPRETATION
Yusen-Ley Cooper1* and James Macnae2
Australia, Canberra, ACT, Australia
2RMIT University, Melbourne, VIC, Australia
1Geoscience
[email protected]
The current induced by an AEM system in the near-surface
circulates preferentially at a distance from the transmitter,
resulting in a section plotted directly below the receiver that is
actually generated from currents induced in the general vicinity
and not in fact directly below the receiver-transmitter system.
The majority of airborne electromagnetic (AEM) data is
processed using stitched consecutive 1D approximations, from
which conductivity and depth varying sections can be produced.
The depth resolution of conductivity using AEM is one of its
best assets and is an important advantage over potential field
methods. In quasi-layered geology, 1D approximate conductivity
sections are stable and reasonably accurate.
Detection of palaeochannels, faults, horsts, grabens and other
laterally varying structures are potential geophysical exploration
targets where 1D approximations may be invalid. Because
of a relatively wide AEM system footprint and 2D geometry,
using stitched 1D approximations or inversions may lead to
conductivity-depth sections that are deceptive. When 2D/3D
discontinuities are present, 1D approximations and inversions
usually predict an incorrect weaker conductor at depth. Within
a conductive layer where conductivity changes with facies or
geometrical thickness, 1D approximations and laterally
constrained inversions work well.
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2D and 3D processing of 2D/3D data is clearly needed, but
existing inversion methods are too slow. Irrespective of the
accuracy of the inversion algorithms, inversion is not an
automatised process, it relies on a good starting model,
constraints and the interpreter’s experience. In particular,
2D/3D structures with abrupt conductivity boundaries inverted
with an isotropic layered assumption must be questioned,
and interpretation checked with forward models.
Day 1 Session 3 Stream 3
PROSPECTING WITH GRAVITY
FTG DATA IMAGING TECHNIQUES FOR GEOLOGICAL
INTERPRETATION
Jade L. Dickinson1*, James W. Robinson1, Colm A. Murphy1
and James R. Brewster2
1Bell Geospace Limited, Aberdeen, United Kingdom
2Bell Geospace Incorporated, Aberdeen, United Kingdom
[email protected]
Full Tensor Gravity Gradiometry (FTG) has previously been
demonstrated to be an effective tool in both the minerals and oil
and gas industries and is routinely collected on both airborne
and marine platforms. FTG captures a greater wealth of
information than partial tensor systems. This extra information
can be used by tensor imaging techniques to enhance target
anomaly definition.
Rotational invariants allow isolated anomalies to be clearly
imaged and separated from linear background features.
Horizontal invariant lineaments enhance linear features and are
used as an efficient edge mapper. Invariant imaging techniques
exploit the full tensor in order to enhance features not easily
identified in single tensor component data.
Calculating geologic strike angles from FTG data allow us to
employ traditional geological analysis tools such as rose
diagrams. The tensor components are rendered using arbitrary
axes; by recomputing the tensor components with an optimal
reference frame we can align the primary axes of the tensor
with the underlying geology. This can produce enhanced
imaging of target features.
The correct application of these techniques improves the
interpretability of the data, providing further insight into the
target geology. This paper describes the application of these
techniques using recent data examples and shows the value
of the FTG in interpretation techniques.
AIRBORNE GRAVITY & MAGNETICS – A FAST TRACK
MULTI-SYSTEM APPROACH FOR PETROLEUM
EXPLORATION
J. Joseph
UTS Aeroquest, Perth Airport, WA, Australia
The gravity method is one of the important techniques used in
modern exploration for petroleum commodities. The need for
acquisition of large gravity data sets at greater speed over highly
prospective areas is renewing demands for airborne gravity
measurement systems. The significance of this method has
increased in recent times with major advances in satellite
ASEG-PESA 2010 Conference Handbook
Abstracts
INTEGRATED INTERPRETATION OF FALCON AIRBORNE
GRAVITY GRADIOMETER, MAGNETIC AND SEISMIC
DATA ACQUIRED OVER THE CHIRETE BLOCK,
ARGENTINA
Luiz Braga1*, M.L. Fernandez2, J.C.S. de Oliveira Lyrio3,
S.V. Yalamanchili1 and A. Morgan1
1Fugro Gravity & Magnetics Services, WA, Australia
2Petrobras Energia, Argentina
3Petrobras, Brazil
[email protected]
Integrated interpretation of high resolution FALCON airborne
gravity gradient and magnetic data with 2D seismic data from
the Chirete Block, onshore northern Argentina, provided
enhanced understanding of the tectonic framework, basement
configuration, and sedimentary structures. Basement related
faults/lineament maps were generated using several
enhancements of gravity gradient and magnetic data. These
were combined with magnetic depth estimates, seismic and
gravity to create an integrated 3D basement model. Seismic
depth sections, velocities, and well logs from nearby
discoveries, were used as constraints for 2.5D and 3D gravity
and magnetic modeling. This enabled key sedimentary features
to be identified and mapped both along and between existing
seismic lines.
Several igneous provinces were identified, and are probably
related to the rift and post-rift periods. A strong correlation
exists between faults derived independently from seismic
reflection data and enhanced Airborne Gravity Gradiometer
data. A number of structural features were identified with the
mapped faulting, which may provide new targets for further
interpretation or drilling.
Day 1 Session 3 Stream 4
PETROLEUM IN ONSHORE BASINS
UNDERSTANDING THE ARCHITECTURE
AND PETROLEUM POTENTIAL OF AUSTRALIA’S
ONSHORE SEDIMENTARY BASINS WITH DEEP
SEISMIC REFLECTION DATA
Lidena K. Carr*, R.J. Korsch, J. Maher, L.E.A. Jones, A. Nakamura
and J. Holzschuh
Geoscience Australia, Onshore Energy & Minerals Division,
Canberra, ACT, Australia
[email protected]
The Onshore Energy Security Program, funded by the Australian
Government and conducted by Geoscience Australia, has
acquired deep seismic reflection data across several frontier
sedimentary basins to stimulate petroleum exploration in onshore
Australia. Interpretation of the new seismic data from these
onshore basins, focusing on overall basin geometry, internal
sequence stratigraphy and petroleum potential, will be presented
here.
At the southern end of the exposed part of the Mt Isa Province,
northwest Queensland, deep seismic line 06GA-M6 was
acquired across the Burke River Structural Zone of the Georgina
Basin. The basin here is >50 km wide, with a half graben
geometry, bounded in the west by a rift border fault.
The Millungera Basin in northwest Queensland is completely
covered by the Eromanga-Carpentaria Basin and was unknown
prior to the seismic imaging of segments of the western part of
the basin in 2006 (06GA-M4 and 06GA-M5). Following this,
seismic line 07GA-IG1 imaged a 65 km wide transect across
the basin. The geometry of the basin fill and a post-depositional
thrust margin indicate that the original succession was much
thicker than preserved today and there is potential for
a petroleum system to exist.
The Yathong Trough, in the southeast part of the Darling Basin
in NSW, has been imaged in seismic line 08GA-RS2, with
several stratigraphic sequences being mapped. Previous studies
indicate that the upper part of this basin consists of Devonian
sedimentary rocks, with known potential source rocks at depth.
In eastern South Australia, seismic line 08GA-A1 imaged
the Cambrian Arrowie Basin, which is underlain by a
Neoproterozoic succession of the Adelaide Rift System. Shallow
drillholes have aided the assessment of the petroleum potential
of the Cambrian Hawker Group, which contains bitumen in
some of the cores, indicating the presence of source rocks in the
basin system.
USING POTENTIAL FIELD DATA FOR PETROLEUM
EXPLORATION TARGETING, AMADEUS BASIN,
AUSTRALIA
Mike Dentith1* and Duncan Cowan2
1The University Of Western Australia, WA, Australia
2Cowan Geodata Services, WA, Australia
[email protected]
The Amadeus Basin, a large Proterozoic basin located in
central Australia, is the least explored onshore petroleumASEG-PESA 2010 Conference Handbook
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ABSTRACTS
positioning technology, which enable accurate, cost-effective
surveys over much larger regions than previously possible. UTS
Aeroquest utilizes the latest version of airborne gravity systems
– TAGS (Turnkey Airborne Gravity System), which is based
on the LaCoste-Romberg Air-Sea Gravimeter concept. TAGS
consist of a highly damped, spring-type gravity sensor mounted
on a gyro-stabilized platform. The 3-D positions and velocities
of the moving platform/aircraft are precisely determined using
data from geodetic quality GPS receivers installed & operated
both on the aircraft and at the ground base station. UTS
Aeroquest has installed the airborne gravity system on a fixed
wing geophysical survey aircraft, which is already equipped with
a magnetic gradiometer acquisition system and radar altimeter.
Prior to offering the services of this new system, a pre-purchase
test over the Polk Country region of Florida, US, was
undertaken. The system performance was tested for,
(a) repeatability along predefined survey flight lines,
(b) crossover errors and (c) comparison with ground data. The
results provided a high level of confidence in offering this
multi-parameter airborne geophysical system to the petroleum
industry. The system has subsequently completed several
successful surveys in Southeast Asia and the Middle East over
the last two years.
Abstracts
bearing basin with proven reserves in Australia. The size
and remoteness of the Amadeus Basin makes ground
exploration expensive.
with poor reservoir properties have been encountered. Thick
Early Permian coal seams may be a future target for deep coal
seam gas.
Carefully processed gravity and magnetic data will be shown
to be useful tools for identifying prospective areas in the
Proterozoic succession in the Amadeus Basin in Western
Australia. Density and magnetic variations within the basin fill,
considered in the context of the likely petroleum system, allow
the ‘signatures’ of prospective areas to be identified.
The Eromanga Basin north of the Cooper Basin is considered
a frontier area, and has received little exploration to
date. However Type II/III Jurassic source rocks in oil
generation window have been intersected in the few wells
drilled. The exploration uncertainties that remain include
the volume of organic rich source rocks, and the presence
of focused migration pathways to potential hydrocarbon
traps.
ABSTRACTS
In the western part of the basin the Gillen Petroleum System is
considered most significant: This system has the important
characteristic that the source is stratigraphically higher than the
reservoir. Thin skinned deformation is expected at the source
level and above, with detachments at evaporitic horizons, but
deformation of the reservoir is expected to be thick-skinned.
This model can form the basis for predicting potential field
responses. The most prospective areas are where
15:30–17:30
Day 1 Session 4 Stream 1
(i) gravity suggests basement (and reservoir) is shallow,
(ii) magnetics maps fold-thrust complexes (structural trap),
(iii) these features occur adjacent to gravity lows, indicative of
significant thicknesses of basin fill (source at depth and
below reservoir).
MINERALS DISCOVERY
Faults at the margins of the depocentre (mapped using
magnetic data) provide a possible migration path for the
hydrocarbons.
Ruth Murdie1*, Tom Cudahy2 and Carsten Laukamp2
1St Ives Gold Mine, Kambalda, WA, Australia
2CSIRO, Kensington, WA, Australia
MINERAL EXPLORATION IN THE ST IVES AREA,
EASTERN GOLDFIELDS, USING GEOPHYSICAL
AND HYPERSPECTRAL DATA
[email protected]
PROVEN AND POSSIBLE PETROLEUM PLAYS
OF THE NORTHERN COOPER AND EROMANGA
BASINS, SOUTH AUSTRALIA
Sandra Menpes
Petroleum & Geothermal Group, PIRSA, Adelaide, SA, Australia
[email protected]
The Cooper and Eromanga basins, spanning northeastern South
Australia and South West Queensland, are Australia’s largest
onshore petroleum province. PIRSA’s recent release of vacant
acreage in the northern Cooper and Eromanga basins in South
Australia has focused attention on the proven and untested
petroleum plays of this area.
The Patchawarra Trough is the main hydrocarbon kitchen for
accumulations in the northern Cooper Basin. Permian source
rocks, comprising coal measures and shales capable of
generating gas and minor oil, are in the oil window in the
Patchawarra Trough. The distribution of hydrocarbon
accumulations is controlled in part by the distribution of regional
seals in the Cooper Basin sequence.
On the western margin of the Patchawarra Trough, numerous
intra-Birkhead Formation oil pools proximal to the Cooper Basin
erosional edge have been discovered in recent years. The
intra-Birkhead channel play is now being actively pursued with
the acquisition of 3D seismic surveys to better image channel
systems. An oil recovery from the basal Birkhead Formation
20 km from the Permian sub-crop edge suggests a wide play
fairway, assuming a Permian source.
Significant unconventional gas potential remains in the Cooper
Basin, in the form of gas in low permeability reservoirs (tight
gas), shale gas and coal seam gas. The Early Permian sequence
in the Patchawarra Trough has the necessary elements for a
Basin Centred Gas System, and overpressured gas sandstones
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Recognising primary versus alteration mineralogy is important to
understanding geological processes that lead to mineral deposits.
In particular, recognising the imprint of invading fluids on the
primary geology using geophysical and hyperspectral airborne
imagery can help locate sites where there may have existed
suitable physicochemical contrasts that precipitated valuable
metals.
In the St Ives area of Western Australia, where there are
extensive occurrences of ultramafic rocks, the effects of both
water-rich and CO2-rich fluids can be recognised through
mapping serpentine-amphibole-magnetite versus talc-carbonate
mineral assemblages respectively. Magnetics has proved
valuable for mapping the serpentised (hydrated) ultramafic rocks
whereas hyperspectral data is now proving its role in mapping
the talc-altered rocks, especially as talc is relatively resistant to
the effects of weathering.
This is especially the case in the St Ives area as airborne
hyperspectral maps reveal surface exposures of talc versus
amphibole versus chlorite, all of which can be identified
in different parts of the same geologically mapped units.
Importantly, amphibole (±serpentine) is typically
coincident with strongly magnetic parts of the ultramafic
units whereas the talc is associated with poorly
magnetic ultramafic units.
The implications for mineral exploration are at least
twofold. First, newly recognised talc-rich areas potentially
represent ultramafic rocks where nickel sulphides may have
developed. Secondly, given that these CO2 rich fluids could
have also brought other metals, such as Au, then recognising
the fluid pathways through the ultramafic rocks is important,
especially when other alteration minerals indicative of K
metasomatism, such as white mica and/or biotite, can be
identified.
ASEG-PESA 2010 Conference Handbook
Abstracts
Carina Kemp1*, Lynsey Brett1 and Russell Mortimer2
1GeoMole Pty Ltd, Eveleigh, NSW, Australia
2Southern Geoscience Consultants, Belmont, WA, Australia
[email protected]
This paper will present a case study from an Australian Nickel
Mine, where both DHTEM and BHR are being used routinely
ahead of mining to delineate mineralization. The paper will look
at how interpreting both data sets in combination can remove
some of the limitations of each technique when used in isolation.
Down hole time domain electromagnetics (DHTEM) is a well
known and effective technique for mapping off hole conductors
in exploration for nickel sulphides. However as mines deepen
and orebodies become more structurally complex, EM data
begins to suffer from poor signal to noise levels and modeling/
interpretation of the anomalies becomes more challenging.
Borehole radar is an effective technique for mapping complex
lithology contact topography and structure surrounding a drillhole.
However interpretation of borehole radar data can be difficult if
done in isolation due to the omni-directional radar antenna. Work
is being done in the area of directional borehole radar by we are
a long way from a commercial system that can be used in mining
environments. This paper will present some methods for
interpreting non-directional radar data in three dimensions. One
of these methods is by combining the interpretation with the
DHTEM results for the same hole. The DHTEM can determine
the direction off-hole of an anomaly and the borehole radar can
give you the detail of the topography of that feature.
Similarly the radar results can provide a constraint for DHTEM
modelling providing a distance to the prospective contact and
some detail of the structure on it. This enables complex noisy
DHTEM data to be modelled more accurately.
The case study will show how complex deep mineralization can
be mapped using a combination of these techniques.
DIRECT DETECTION OF IRON ORE MINERALISATION
WITH INDUCED POLARISATION AT THE MARAMPA
IRON ORE DEPOSITS, SIERRA LEONE
Matthew Cooper1* and Kim Bischoff2
Potentials, WA, Australia
2Cape Lambert Iron Ore, WA, Australia
1Resource
[email protected]
Marampa Iron Ore (SL) Ltd, a subsidiary of Australian based
company Cape Lambert Iron Ore Ltd, holds a 319 km2
exploration licence surrounding the old mines at Masaboin and
Gafal. Since early 2009 Cape Lambert has completed detailed
regional mapping over the licence, and outlined several targets
prospective for iron ore. Following detailed trenching and
mapping, diamond drilling of the Gafal West prospect started in
late June 2009. Cape Lambert have estimated a target size of
400–500 million tonnes of iron ore from the known prospects.
hematite bands and the gneissic units. The gravity surveys had
limitations on directly targeting high grade zones, due to
topography, depth and the complex folding.
In order to more fully understand the mineralisation,
petrographic analysis of drill core was completed and
indicated that the high grade zones (>30% Fe) had substantial
chargeability responses, orders of magnitude greater than the
lower grade ore or host rock. Based on these outstanding and
somewhat unexpected results, a program of Induced Polarisation
surveys were commissioned to validate the laboratory results.
This paper reviews the geophysics completed over the Marampa
Iron Ore deposit and highlights the exciting Induced Polarisation
results, which are believed to be a first in iron ore exploration.
STRUCTURAL ANALYSIS OF THE SOUTHERN
ASHANTI BELT, GHANA, USING AIRBORNE
GEOPHYSICAL DATA
Stephane Perrouty1*, M. Jessell1, L. Baratoux1,2, L. Ailleres3
and Y. Bourassa4
1Université Paul Sabatier, Toulouse, France
2Institut de Recherche pour le Développement, Toulouse, France
3Monash University, Melbourne, VIC, Australia
4Golden Star Resources Ltd
[email protected]
The southern Ashanti Greenstone Belt in Ghana is an area of
major economic importance for West Africa, where many
companies are actively exploring for gold. As a consequence,
a significant geological data set has been collected over the
years, but it has not always been subjected to an integrated
interpretation, especially away from the main Ashanti fault
system and the Tarkwaian portion of the belt, such as around
the Wassa Mine. The gridded resolutions of the regional and
mine-scale airborne geophysical surveys are 100 m and 25 m
respectively. Using this geophysical data and field observations,
we have revised the geological and structural map of the south
of Ashanti Belt, and have produced a new map around the
Wassa mine. Along cross-section of these maps, the inversion
of the data with GM-Sys allows us to extend the map in the
third dimension.
These new data, combined with previous studies in the area,
suggest the presence of 4 or 5 deformation events, associated
with plutonism between 2200 and 2000 Ma: a first phase of
NW-SE shortening (D1), previous to Tarkwaian sediments; after
them, a second phase of this shortening (same orientation) (D2
or D1b), mainly characterized by large folds oriented NE-SW in
the Birimian and the Tarkwaian. The next phase of shortening
(D3 or D2b) is oriented WNW-ESE and presents 100–1000 m
wavelength folds on each side of the Ashanti Belt. At local
scale, we can see other deformation events (D4, D5?), with
subhorizontal cleavage and folds or with reactivation of
previously structures.
The next step will be the 3D modeling to finally understand
the structural and temporal relationship between the observed
structures.
Previous geophysical surveys over the area included gravity and
aeromagnetics. These surveys contributed to the geological
knowledge of the area, with the gravity particularly successful at
finding near surface specular hematite mineralisation. Magnetic
surveys have provided limited information as there is minor
(2–5%) late stage disseminated magnetite associated with the
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ABSTRACTS
MAPPING NICKEL MINERALIZATION AHEAD
OF MINING USING DHTEM AND BHR
Abstracts
Day 1 Session 4 Stream 2
IN MEMORY OF SHANTI RAJAGOPALAN: MAGNETIC
INNOVATION
A SUPERCONDUCTING MAGNETIC TENSOR
GRADIOMETER FOR UNDERWATER UXO DETECTION
Jeanne A. Young1*, S. T. Keenan1, D. A. Clark1, K. E. Leslie1, P. Sullivan1,
P. Fairman1, C. Williams1, C. P. Foley1 and S. D. Billings2
1Wealth from Oceans National Research Flagship, CSIRO Materials
Science and Engineering, Australia
2Sky Research Inc., Vancouver, Canada
ABSTRACTS
[email protected]
Throughout the world there are many millions of acres of the
marine environment contaminated by unexploded ordnances
(UXO), either through past military activity (training or warfare)
or deliberate disposal of unwanted munitions. To address this
problem, we are building an underwater magnetic tensor
gradiometer based on high temperature superconducting quantum
interference devices (SQUIDs). The system will have inherently
higher sensitivity and immunity to external noise than
conventional magnetic sensor systems, thus improving detection
performance in the difficult marine environment.
Gradient tensor measurements have a number of benefits over
measuring total field intensity or its vector gradient: they provide
detailed information about a target in a single pass, without
necessarily passing directly over the target; they determine the
location of the target using a direct method, rather than the
indirect inversion method required with other measurements; and
they determine the magnetic moment magnitude and orientation
of the target directly, aiding discrimination between sources and
characterization of the munitions.
Technical challenges for the project include: designing a high
temperature SQUID device that can achieve the required
gradient sensitivity in motion; developing a gradiometer housing
that can deal with the boil-off gas from the liquid nitrogen
cryogen while underwater; identification and removal of
wave-induced magnetic noise; compensation for magnetic noise
caused by motion and the platform itself; and developing a
dipole-tracking algorithm for gradient tensor measurements that
is both robust and computationally undemanding. This paper
will present the progress to date on this project including an
evaluation of gradiometer performance in laboratory conditions.
PRECISION GEOLOCATION OF ACTIVE
ELECTROMAGNETIC SENSORS USING STATIONARY
MAGNETIC SENSORS
Keith Leslie1*, K. Blay1, D. Tilbrook2, S. Billings3 and L. Pasion3
Materials Science and Engineering, Australia
2Retired CSIRO
3Sky Research Inc., Vancouver, BC, Canada
1CSIRO
[email protected]
EMI is generally considered to be the most promising
technology for discriminating between UXO and non-UXO
items. Techniques for EMI-based discrimination generally
depend on the accurate recovery of the parameters of a physicsbased model that can reproduce the observed anomaly. The EMI
response is typically modeled as a dipole through a magnetic
polarization tensor, which provides a model vector to infer target
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characteristics. The success of dipole model based discrimination
algorithms depends on the accuracy with which the axial and
transverse components of the polarization tensor can be estimated.
With noisy and inaccurately positioned data it is difficult
to constrain the depth and location of the item, leading to
considerable uncertainty in the magnitude and ratio of the
components of the polarization tensor. Accurate position location
becomes difficult in wooded environments, where access to
either GPS or laser positioning becomes problematic.
The feasibility of using the magnetic field produced by an
un-exploded ordnance (UXO) detection cart as a means to
accurately locate the cart’s position has been considered and
trialled. This paper will present the results of some preliminary
work, undertaken as part of a SERDP funded SEED project
number MM-1643, that indicates that this technique could
provide a solution to tracking a cart in a wooded environment.
EFFECT OF MAGNETIC FIELD DIRECTION AND SOURCE
ORIENTATION ON DEPTH ESTIMATION SOLUTIONS
Madeline Lee*, W. Morris and H. Ugalde
McMaster University, School of Geography and Earth Sciences,
Hamilton, Ontario, Canada
[email protected]
Most semi-automated processing routines assume simple
scenarios where the resultant anomaly is produced by a single,
parallel-piped, non-dipping source in a vertical ambient field.
This however does not represent many real-world situations.
All magnetic sources will have some dip and are not oriented
parallel with, or orthogonal to the ambient magnetic field.
Therefore, the angle at which the magnetic field intercepts the
source will not be the same along all edges. This discussion is
further complicated when one considers whether the source is
2D or 3D, which depends on where calculations are conducted
along the source edge. This raises the critical question – how
does the magnetic field direction affect depth solutions along the
source edges, which each have a different orientation?
Tilt-depth has been shown to work reliably under ideal
conditions. Since tilt-depth is a simplified formula using the
assumption of a vertical magnetic field, one needs to revisit its
fundamental equations. As it turns out, the fundamental
equations do employ the basic magnetic field geometry
parameters, inclination and declination, and the source’s dip
angle. Reworking these formulae shows it is incorrect to assume
that the same depth solution will be produced regardless
of the source orientation relative to the magnetic field. The
consequence of this effect becomes apparent through a solution
asymmetry on either side of the source edge. By varying the
field parameters in a synthetic scenario, it is shown that variable
depth solutions are achieved depending on both the planar
orientation and dip of the magnetic source.
COMPENSATION OF THE FULL MAGNETIC TENSOR
GRADIENT SIGNAL
Dominik Argast*, Desmond Fitzgerald and Horst Holstein
Intrepid Geophysics, Brighton, VIC, Australia
[email protected]
In recent developments a full tensor magnetic gradient system
has been deployed in South Africa. The instrument is made by
IPHT (Institute of Photonic Technology, Jena, Germany) and
ASEG-PESA 2010 Conference Handbook
Abstracts
Issues that are covered include drift correction of the Euler
Angles from the INS (inertial navigation system), removal of
flux jumps from the SQUID and recovering the three
components of the ‘B’ field.
A novel ‘least squares’ rotational adjustment of the tensor signal
in a moving window is proposed as an extra compensation step
to achieve higher spatial coherency of the curvature gradients.
This new method is demonstrated with the Platreef survey from
the Bushveld.
Day 1 Session 4 Stream 3
INDUSTRY PERSPECTIVE
KEYNOTE ADDRESS: FINANCING UPSTREAM OIL
AND GAS PROJECTS
Measurements of achieved resolution on data recorded in 1941
show better resolution than typical for 2007. Intervening years
are generally consistent with the long term trend, with a slight
increase in resolution from a low point in the 1970s.
Seismic data from 1930 to 2007 has been measured to determine
the resolution of the reflections recorded. The data come from
locations in North America, Latin America, Africa and Asia, but
many from Australia. The earliest data is from paper records
held by the Geophysical Society of Houston. For each data set
a resolution constant is determined from the dominant reflection
frequency as a function of reflection time. We have examined
the variation in this constant in the seventy plus years to 2007.
Although area dependent, we find that the overall trend has not
been towards an improvement in resolution, but the reverse.
This is despite the substantial advances in all aspects of data
acquisition and processing, particularly over the last forty years.
Many of the techniques used to improve other aspects of the
data signal to noise ratio, horizontal resolution and lithology
discrimination, in particular probably limit time resolution.
In most projects there is a tradeoff between cost, resolution and
noise. The chosen techniques always seem to result in similar
resolution, and this suggests that the cost in money or other
desirable signal characteristics of improving resolution beyond
this level is very high.
Vanessa Lenthall
Division Director, Metals and Energy Capital Division, Fixed
Income, Currencies and Commodities,
Macquarie Group Limited
[email protected]
COLLABORATIVE R&D IN AUSTRALIA – A 50 YEAR
JOURNEY
Joe Cucuzza*, Alan Goode and Juan Daniel Silva
AMIRA International
[email protected]
Measurements of achieved resolution on data recorded in 1941
show better resolution than typical for 2007. Intervening years
are generally consistent with the long term trend, with a slight
increase in resolution from a low point in the 1970s. Seismic
data from 1930 to 2007 has been measured to determine the
resolution of the reflections recorded. The data come from
locations in North America, Latin America, Africa and Asia,
but many from Australia. The earliest data is from paper records
held by the Geophysical Society of Houston.
There is increasing demand for finance for upstream oil and gas
projects in Australasia.
With the growth in experience of Banks in the energy sector
and the turbulence of the share market in the past 18 months
increasingly many companies are looking for debt to assist
with acquiring and developing projects.
This paper considers the finance options available to upstream
oil and gas companies including what type of debt might suit
projects at different stages of development.
THE HISTORY OF SEISMIC RESOLUTION
John I. Denham1* and Les R. Denham2
J&J Denham, Elong Elong, NSW, Australia
2II&T, Houston, Texas, USA
1Consultant
[email protected]
ASEG-PESA 2010 Conference Handbook
For each data set a resolution constant is determined from the
dominant reflection frequency as a function of reflection time.
We have examined the variation in this constant in the seventy
plus years to 2007. Although area dependent, we find that the
overall trend has not been towards an improvement in resolution,
but the reverse. This is despite the substantial advances in all
aspects of data acquisition and processing, particularly over the
last forty years. Many of the techniques used to improve other
aspects of the data signal to noise ratio, horizontal resolution
and lithology discrimination, in particular probably limit time
resolution. In most projects there is a tradeoff between cost,
resolution and noise. The chosen techniques always seem to
result in similar resolution, and this suggests that the cost in
money or other desirable signal characteristics of improving
resolution beyond this level is very high.
AMIRA International (www.amirainternational.com) has
operated for over 50 years as the mineral industry’s not-forprofit research association following its establishment in 1959
in Melbourne by the leaders of Australia’s major mining
companies. Its main function is to develop, broker and
administer collaborative research projects in geoscience,
AUGUST 2010
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59
ABSTRACTS
flown by helicopter. In developing a ‘custom’ solution for taking
the raw signal through to a final local geophysically sound data
base, one of the biggest challenges has proven to be the
compensation of aircraft / bird rotational movements, so that the
reported curvature gradients in the world co-ordinate system are
as free of these rotational errors as possible.
Abstracts
exploration, mining, mineral processing and sustainability
with leading research groups around the world for the benefit
of its member companies.
ABSTRACTS
Numerous technical problems in the mining industry are shared
by many companies, and significant benefits are gained by
sharing the costs and risks between sponsor companies for
important but relatively non-competitive areas of research. Over
650 projects have been completed, with many contributing to
significant financial benefits for the sponsoring companies and
many now forming the core of “standard industry practice”.
AMIRA projects have also had a major impact in developing
Australian research infrastructure and capabilities, particularly
through the cooperative support of Australian Government
leveraged funding. AMIRA projects have also promoted an
important framework to train students for future roles in
companies or as researchers.
AMIRA’s development has reflected the changing nature and
attitudes of the mining industry over time. Its most recent
change has been its “internationalisation” as its members have
recognised the value of the “AMIRA model” in a global context.
Offices have now been established in Santiago, Denver and
Johannesburg aimed particularly at promoting local projects for
local needs and developing local research capabilities while also
continuing to seek the best available researchers to solve global
problems for the industry.
While AMIRA researchers have been actively working on
Chilean deposits for many years, recently new projects have
begun with Chilean universities dealing with specific Chilean
issues, often with international implications. As in Australia,
the industry funding is starting to be matched by supportive
government funding through CORFO.
There are numerous lessons to be drawn from AMIRA’s
experience over the last 50 years, many of which could assist
countries like Chile in development of their own unique
innovation systems.
MYTHS EXPOSED ON WHAT CONTROLS BASE
METALS AND GOLD PRICES
Noll Moriarty
Archimedes Financial Planning, Aspley, QLD, Australia
• Reality: prices are slightly inversely related to economic heath
(as GDP increases, US dollar rises which has negative effect
on commodity prices).
• “Gold and base metal prices are controlled by different factors.”
• Reality: both prices are strongly influenced by US dollar.
• “Gold price is likely to keep appreciating during the next 2–5
years.”
• Reality: gold price current upswing has the strong appearance
of a speculative bubble; on the balance of probabilities, the
US dollar will appreciate and reduce the gold price.
Day 1 Session 4 Stream 4
PETROLEUM IN ONSHORE BASINS
INTERPRETATION AND MODELING OF THE PEDIRKA
BASIN (CENTRAL AUSTRALIA) USING MAGNETICS
AND GRAVITY
Christopher Bishop* and Mike Dentith
The University Of Western Australia, WA, Australia
[email protected]
The Pedirka Basin straddles right centrally on the Northern
Territory – South Australian border. The area includes other
sedimentary basins and together they form the AmadeusPedirka-Simpson-Eromanga basin system. Much of the region
has exploration licences, however hydrocarbon and coal
exploration has been negligible compared to the nearby Cooper
Basin region, with the first drilling activity for decades taking
place in 2008. Seismic interpretation has been almost the
primary source for interpretations in the area. Given the sparse
nature of this data there is still a great deal of ambiguity in
important structural information.
Recent airborne magnetic data and gravity data is now available
over the Pedirka area however this data has not been fully
exploited to date. Exploration over the Pedirka Basin is now
looking for the deeper, more thermally mature source areas in
the troughs. The aim of this research is to capitalize on this
potential field data for interpretation and modeling purposes
in order to gain new insights into the structures, depths and
boundaries of the region.
[email protected]
Conventional wisdom is that base metal prices are set primarily
by the interaction of supply (existing and new production) and
demand (global economic activity). Gold prices are set in
accordance with inflation rates, exchange rates and the status
of the global geopolitical situation. Since different factors affect
these commodities, there should not be a link between US dollar
prices.
This paper questions the relevance of such approaches,
demonstrating instead that the major underlying control on
commodity prices is appreciation and depreciation of the United
States Dollar. Since the U.S. Dollar has just risen above a
40-year low, it must be more likely that the currency will
appreciate, or remain stable, than depreciate significantly.
This would have downward pressure on commodity prices.
The paper looks at common myths vs. reality, such as:
• “Base metal prices are driven by economic health, supply and
demand.”
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CARBONATE FRACTURE PERMEABILITY
CHARACTERIZATION – A CASE HISTORY
Brian H. Link1* and Inga Y. Khromova2
Technologies Inc, Calgary, Canada
2Lukoil, Moscow, Russia
1Tetrale
[email protected]
Duplex wave migration is a new depth imaging technology that
is capable of delineating vertical or near vertical boundaries
within the reservoir. This is a direct detection method that
observes the relative change in lateral acoustic impedance –
in other words, it detects lateral heterogeneities within the
reservoir. During the development of one of the oilfields in the
Timano-Pechersky basin, after extensive pattern drilling, it was
observed that the wells exhibited extreme variations in
production rates despite the fact that the well logs indicated that
there were little or no lithologic or petrophysical changes across
the reservoir. It was apparent that the rate of production was
highly dependent on the fracture systems within the carbonate.
ASEG-PESA 2010 Conference Handbook
Abstracts
SHALLOW VERTICAL SEISMIC PROFILING
EXPERIMENTS WITH A SURFACE IMPACT SOURCE
AND A CEMENTED 3-C GEOPHONE STRING;
PERTH BASIN, WESTERN AUSTRALIA
Brett Harris*, Christian Dupuis and Milovan Urosevic
Curtin University of Technology, Bentley, WA, Australia
[email protected]
Analysis of first arrivals recorded by a total of 24 cemented
geophones from a surface source provides insight into the
propagation of acoustic waves. A set of surface to hole
experiments have been carried out to measure variations
of transit times, frequency content and amplitudes of the
downgoing (transmitted) compressional waves. The geology
of the test site is tightly constrained by wire-line and geological
logs from more than 20 close spaced drill holes. One experiment
consisted of 274 repeat blows from a surface impact source 25 m
away from a vertical string of 3-C geophones cemented in a drill
hole. The geophones spanned a depth range from 74 to 284 m.
A detailed comparison of total travel time and interval travel
times demonstrate a surprisingly high level of repeatability
across 274 repeated shots at the same position. Experiments with
repeat radially symmetric source positions located around the
cemented 3-C geophone string were also carried out. These
ASEG-PESA 2010 Conference Handbook
experiments indicated that even a slight change in source
location or condition can significantly change the shape of the
waveform generated at the surface. This was likely the result on
slight variations at the source ground interface.
2.5 D FORWARD MODELING – A COST EFFECTIVE
SOLUTION THAT RUNS ON SMALL COMPUTING
SYSTEMS
Alex Kostyukevych1* and Yuriy Roganov2
1Tetrale Technologies Inc., Calgary, Canada
2Ukrainian State Geological Prospecting Institute, Kiev, Ukraine
[email protected]
Full wave elastic forward modeling from full 3D depth models
to produce 3D–3C shot records is extremely compute intensive.
A methodology has been developed that enables geophysicists to
utilize an extremely complex geologic model in the X direction,
but that is consistent in the Y direction to produce 3D–3C full
wave elastic forward modeling results. This methodology can be
successfully used to test the viability of recording parameters in
thrust belt environments that exhibit extremely complex
structures in the dip direction but relatively stable structures in
the strike direction. Many other geologic situations involving
fracture systems can be effectively modelled using this
technology. The method is capable of taking into account the
quasi-anisotropic and velocity dispersion effects of thin beds.
Also, for the case of TTI anisotropy (or tilted fracturing, or
some combination of tilted fracture systems) 2.5 D modeling
allows us to simulate both “fast” and ‘slow” shear waves and
also simulates the effects of wave coupled refraction. In
addition, Q parameters for P and S waves can be defined to
accurately simulate polarization effects for both surface waves
and volume waves. The accuracy of the method is such that
geophysicists can predict the azimuthal AVO and velocity
effects of fracture systems and test the effectiveness of full
elastic inversions and various seismic methods that are available
to measure azimuthal variations of seismic parameters. The
mathematical derivation of the process will be discussed and
examples of the usage of 2.5 D forward modeling in exploration
will be illustrated.
AUGUST 2010
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61
ABSTRACTS
The economics of the play required that Lukoil find a way to
accurately delineate these fracture systems, understand the related
permeability characteristics and how they effected the required
drilling strategy in different areas in the basin. Lukoil conducted
an extensive study of several conventional fracture detection
methodologies including reflection curvature, coherency cube
analysis, wave field spectral decomposition and azimuthal
anisotropy. All of these methods were found to be inconclusive
with regard to their ability to reliably delineate the fractures.
Since the fractures had zero throw the methods that required
some structural deformation simply did not work and all methods
correlated poorly with well results. Subsequently, duplex wave
migration was tried on the project and it not only confirmed the
known results, but it also enabled better delineation of separate
lineal anomalies and their later categorization according to their
permeability and sealing properties.
Abstracts
Day 2: Tuesday 24 August 2010
8:30–10:30
Day 2 Session 1 Stream 1
INNOVATIONS IN GEOPHYSICAL INVERSIONS
KEYNOTE ADDRESS: INTEGRATED INTERPRETATION
OF GEOLOGY AND GEOPHYSICS, USING INVERSIONS,
TO PREDICT GEOLOGY UNDER COVER
Nicholas Williams
Airborne EM Project Leader (Acting), Onshore Energy and Minerals
Division, GeoScience, Australia
ABSTRACTS
[email protected]
ways to extract information from complex datasets in situations
where direct measurement is not possible. Such inverse
problems are ubiquitous across the physical and mathematical
sciences and are central to discovery of resources within the
Earth upon which Australian society is dependent. A recurring
problem is connecting the ‘domain’ specialist who understands
the nature of the particular data at hand, e.g. those who collect
and interpret wireline log measurements down boreholes, with
those who specialize in the often mathematical or computational
methodologies that could extend interpretation of such data.
Who hasn’t encountered the theoretician who sounds like they
have something useful to offer, if only we could understand
what they are talking about? A key challenge is in closing the
communication gap. For several years now the Centre for
Advanced Data Inference (CADI) at ANU has been focused on
this issue. We have often found that a valuable contribution can
be in identifying where established methodologies from one field
can be profitably used in another. Examples of such projects are
presented. These include a recent focus which is on developing
new ways of reliably detecting discontinuities in 1-D, 2-D or
3-D spatially varying signals.
DOWN THE BOREHOLE BUT OUTSIDE THE BOX:
INNOVATIVE APPROACHES TO WIRELINE LOG
DATA INTERPRETATION
Obtaining reliable predictions of the subsurface will provide a
critical advantage for explorers seeking mineral deposits at depth
and beneath cover. A common approach in achieving this goal
is to use deterministic property-based inversion of potential
field data to predict a 3D subsurface distribution of physical
properties that explain measured gravity or magnetic data. The
non-uniqueness of inversions of potential field data mandates
careful and consistent parameterization of the problem to ensure
realistic solutions. Including all prior geological knowledge as
constraints on the inversion also helps ensure that the recovered
predictions are consistent with both the geophysical data and the
geological knowledge.
We review how potential field inversions are best applied for
mineral exploration problems using the UBC-GIF inversion
algorithms. We use examples to emphasise the importance of
mesh design and applying appropriate data processing, and
identify the approach for defining key parameters such as data
uncertainty, potential field weighting functions, and numerical
parameters that approximate prior geological knowledge of
in situ trends, geometries and properties. Consistent application
of these techniques will ensure the most reliable predictive
physical property models for explorers.
DATA INFERENCE IN THE 21ST CENTURY: SOME IDEAS
FROM OUTSIDE THE BOX
Malcolm Sambridge
Research School of Earth Sciences, Australian National University,
Canberra, ACT, Australia
[email protected]
A major driver for the advance of science is the feedback
between predictions and observations. During the 21st century
scientific discovery and its impact on all areas of human society
will depend on our ability to draw robust conclusions from
complex observations. The focus of this presentation is on new
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Anya M. Reading1*, Thomas Bodin2, Malcolm Sambridge2,
Stephanie Howe1 and Michael Roach1
1School of Earth Sciences and CODES Centre of Excellence for Ore
Deposits, University of Tasmania, Hobart, TAS, Australia
2Research School of Earth Sciences, Australian National University,
Canberra, ACT, Australia
[email protected]
Wireline logs record the variation in a number of physical
measurements, sometimes 20 or more different properties, with
depth down a borehole. They are routinely correlated with, and/or
interpreted in terms of, the rock stratigraphic record. Logs are
also interpreted with the aim of inferring other useful physical
properties not directly measured. In some data-rich exploration
industries, such as oil and gas, wireline log interpretation is
highly developed. In other industries, such as geothermal and
minerals exploration, wireline information is often incomplete
and may be inaccurate or inconsistent. The aim of this work is
to explore innovative approaches to the analysis of wireline logs.
The aims are two-fold: 1) Use a flexible approach to the
identification of ‘change points’, which may indicate boundaries
between lithologies or significant intra-formation structure, and
2) Predict new, useful rock properties, such as thermal conductivity,
from the available wire-line data. We examine, for example,
methods where the number of boundaries/classes is not fixed in
advance, being solved for as part of the modelling process. We
also test a range of approaches to the regression problem aimed
at predicting a useful property from other measured values. The
approaches are applicable in data-rich environments with
relatively well-know stratigraphy where they will add to physicsbased inference. They may also find particular utility in
situations with less than ideal data and diverse stratigraphy as
they naturally incorporate ways of handling uncertainty.
Unforeseen relationships are allowed to emerge and, hence,
inform future predictive analysis.
ASEG-PESA 2010 Conference Handbook
Abstracts
Richard Lane* and Peter Petkovic
Geoscience Australia, Canberra, ACT, Australia
[email protected]
Gravity modelling of the Capel-Faust region was carried out to
determine whether an interpretation of reflection seismic data,
knowledge of mass density properties, and inferences drawn
from various other available geological and geophysical data
were consistent with the observed gravity data (i.e., within the
higher probability regions of certainty for each of the data sets).
The shipborne complete Bouguer anomaly (CBA) gravity data
for the region were modified to better represent the real world
by incorporating the gravity effects of (1) the vertical separation
between the observation points on the geoid and the ellipsoid
surface (i.e., the indirect effect), and (2) global relief beyond the
truncated spherical cap region (i.e., the distant relief effect).
The upper crustal mass density model derived from a depthconverted interpretation of reflection seismic data and sonobuoy
refraction seismic data was supplemented by a crust-to-mantle
Moho boundary derived from the global CRUST2.0 geological
model and from local isostatic considerations. The degree of
consistency between the gravity effect of this model and the
modified CBA data was examined using a combination of
modelling techniques employing (a) forward modelling of the
gravity effect of a mass density model, (b) bounded least squares
optimisation of mass density values for the various regions in
the corresponding lithological model, and (c) generation of an
ensemble of linked lithology and mass density models. The
latter used a Markov Chain Monte Carlo (MCMC) procedure
to modify the boundaries of the lithological regions and random
assignment of mass density values from probability distributions
defined for each of the lithologies in the models.
Day 2 Session 1 Stream 2
TECHNOLOGY ADVANCES
APPROACHING 10 MICROSEC (AND EARLIER)
WITH THE SKYTEM SYSTEM
Esben Auken1*, Anders Vest Christiansen2 and Andreas Viezzoli3
1Department
of Earth Sciences, Aarhus University, Denmark
Survey of Denmark and Greenland, Denmark
3Aarhus Geophysics ApS, Denmark
2Geological
[email protected]
In many applications the resolution of near surface geological
layers are of great importance. A number of groundbased
transient electromagnetic systems (TEM) provide sufficient early
time data enabling such a resolution whereas this has not been
possible with airborne TEM systems. Until now.
In this abstract we describe the latest development of the
SkyTEM system where early time data from as early as
8 microseconds (from begin of ramp) can be used even with a
500 m2 transmitter frame and a maximum magnetic moment of
approx. 160 000 Am2. The system itself provides unbiased data
from around 14 microseconds, but because the bias response at
earlier times is 1) dependent of the transmitter coil geometry
ASEG-PESA 2010 Conference Handbook
only, 2) it is constant from flight to flight and 3) it can be
estimated from high altitude measurements, the amplitude of the
bias response can be determined during the inversion process
and thereby modeled.
Using the Laterally Constrained Inversion algorithm to correlate
the amplitude from sounding to sounding we show that data
from as early as 8 microseconds from begin of ramp can be
included in the inversion process. The inverted sections have
been successfully validated against ERT measurements on the
ground and 6 boreholes to a depth of 25 m with both geological
descriptions, resistivity logs and gamma logs.
In the larger perspective the method can be used to accurately
estimate near surface layers thus avoiding expensive and
logistically challenging groundbased geophysical campaigns.
DERIVING THE COMPLETE GRAVITY GRADIENT
TENSOR FROM THE VERTICAL COMPONENT
OF GRAVITY BY A COSINE TRANSFORM TECHNIQUE
Fuyu Jiang1* and Likun Gao2
University, Department of Earth Science & Engineering,
Nanjing, China
2Nanjing University, State Key Laboratory for Mineral Deposits
Research, School of Earth Sciences & Engineering, Nanjing, China
1Hohai
[email protected]
A Cosine transform technique has been developed to calculate
the complete gravity gradient tensor from pre-existing vertical
gravity data which provides an alternative determination of the
gravity gradient tensor components. Gravity gradient tensor
components are computed for a three-dimensional buried right
rectangular prism model. A comparison between the discrete
Cosine transform (DCT) results and forward calculating gradient
components from the 3D model shows that the root-mean-square
error for each component, between the two results, is at most
2.16 Eotvos Units. In addition, according to another comparison
between this DCT technique and FFT method, there is a larger
enough error between the FFT derived and model derived, but
the results of DCT derived coincide well with the model derived
except for several data of the boundary because of remains of
Gibbs’ effect, indicating that our technique is more efficient than
traditional FFT method.
RAPID GRAVITY AND GRAVITY GRADIOMETRY
TERRAIN CORRECTIONS VIA A QUADTREE MESH
DISCRETISATION
M. Andy Kass*, Kristofer Davis and Yaoguo Li
Colorado School of Mines, Colorado, USA
[email protected]
We present a new method for modeling surfaces in gravity
gradiometry surveys utilising an adaptive quadtree mesh
discretisation. The method is tailored to provide rapid and
accurate terrain corrections for draped airborne surveys, but
also is appropriate for the forward model of any surfaces in
gravity gradiometry exploration such as basement contacts. The
surface used in the modeling is discretised automatically to the
largest cell size that will yield the user-specified accuracy,
resulting in much faster computation than a full resolution
approach. We show that the adaptive quadtree method can
reduce the computational cost in terrain corrections by two to
five orders of magnitude. Thus the method has an efficiency
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ABSTRACTS
GRAVITY MODELLING OF THE CAPEL-FAUST
REGION – A WORKFLOW WITH GLOBAL TO LOCAL
SCALE ELEMENTS
Abstracts
approaching that of Fourier-domain based methods, but without
the restriction of a planar observational surface. For instance,
the full gravity gradient terrain correction for a mineral
exploration survey of 1000 line km covering 100 square km is
completed in 4 h on a single core PC. We also extend the
method to terrain corrections in airborne and ground gravity
surveys measuring the vertical component of the gravity field.
AUSCOPE NATIONAL VIRTUAL CORE LIBRARY –
SA NODE
Alan J. Mauger
PIRSA, Adelaide, SA, Australia
[email protected]
ABSTRACTS
The AuScope National Virtual Core Library (NVCL) provides
desktop access to all Australian State Government core storage
facilities in such a way that a geologist can assess the spectral
properties, imagery and mineralogy of drill core prior to
making a physical inspection. The potential to reduce
logging ambiguity will impact on exploration efficiency and
effectiveness.
The heart of the NVCL is a partnership between the CSIRO
HyLogger™ instruments and sophisticated analytical software
with the capacity to serve large volumes of data over the
internet. South Australia’s a collection of over 300 open file
spectrally scanned drillholes forms the basis of the SA Node of
the NVLC. HyLogger™ records a 0.1 mm resolution image
while spectra are collected every 1 cm. Visible to shortwave
infrared (400–2500 nm wavelength) reflected light spectra
display distinctive absorption features which enable direct
identification of minerals containing O-H and C-O bonds. Using
“The Spectral Geologist” (TSG) software the geologist is able to
place a cursor on the image of the core and read directly the
spectra and interpreted mineralogy for that location. TSG
provides the functionality to interact with a relational database
which will be open to the internet.
Applications for this technology include 3D mapping of
alteration systems associated with ore deposition. Being able to
semi-quantify the abundance of minerals geographically enables
geologists to include Eh and pH conditions in their targeting
models. Mapping chemical variations in individual mineral
species has shown to be an empirical vector to ore permitting
refinement of greenfield drilling programs.
Day 2 Session 1 Stream 3
GEOPHYSICS AND GEOTHERMAL APPLICATIONS
CHARACTERISING UNCERTAINTY WHEN SOLVING FOR
3D TEMPERATURE: NEW TOOLS FOR THE AUSTRALIAN
GEOTHERMAL ENERGY EXPLORATION SECTOR
Helen Gibson1, Ray Seikel1 and Tony Meixner2
1Intrepid Geophysics, Brighton, VIC, Australia
2Geoscience Australia, Canberra, ACT, Australia
[email protected]
Australia’s emerging geothermal energy industry is now widely
exploring for potential Enhanced Geothermal System (EGS)
plays. Components of these plays typically include: high heat
64
PREVIEW
AUGUST 2010
producing granites in combination with overlying thermally
insulating units such as shales or coal seams. Once the heat
resource is proven to contain anomalously high temperatures
at accessibly shallow depths, the key to sustainable energy
production is in maintaining fluid flow via natural or induced
reservoir porosity, or fracture networks.
These geological requirements of an EGS play must be mapped
in 3D in order to investigate the play potential, and facilitate
accurate in-situ temperature and heat flow modelling. 3D
GeoModleller is one such software tool able to do both: build an
easily editable 3D geology model, and calculate 3D temperature
directly from the model. In solving for temperature, accounting
for heat conduction and internal heat production, thermal rock
properties of the geology volumes (i.e., thermal conductivities
and heat production rates) are required.
Recent improvements to GeoModeller allow for the input
thermal properties to be specified as distribution functions.
Repeated parameter sweeping of these distributions for each
geology unit occurs allowing multiple models to be generated
that include the spans of extreme thermal properties settings.
Multiple thermal simulations are then undertaken, and statistical
analysis of the results is used to characterise uncertainty within
the in situ heat resource, reducing the risk of EGS energy
exploration.
A METHOD FOR CALIBRATING AUSTRALIAN
TEMPERATURE-DEPTH MODELS
Desmond Fitzgerald* and Ray Seikel
Intrepid Geophysics, Brighton, VIC, Australia
[email protected]
The Australian geothermal industry is moving rapidly and in that
process, requires a lot from geophysics to aid in characterising
regional prospectivity for exploitable heat resources.
Various groups are using hybrid methods to estimate ‘Curie
point’ temperatures at depth, or alternatively, the temperature at
5 k below the surface. Deep drilling observations and airborne
magnetics compilations are the key components, together with a
basement geology interpretation. Several generations of this
work are already published with more to come.
A method to test these maps and also help characterise
uncertainty is proposed based upon a deep 3D model continental
scale, extending to the lithosphere. Variable surface temperature
and heat flow grids, based upon remote sensing are used,
together with a simple lithosphere boundary condition. The heat
diffusion is then employed to test the temperature-depth maps.
Progress on applying this method to Australia is reported.
THE APPLICATION OF GEOLOGICALLY-CONSTRAINED
3D HEAT CONDUCTION MODELS TO GEOTHERMAL
EXPLORATION
Craig O’Neill1*, Cara Danis1, Raquibul Hassan1, Steve Quennette2
and Louis Moresi3
1Macquarie University, Sydney, NSW, Australia
2Victorian Partnership for Advanced Computing, VIC, Australia
3Monash University, VIC, Australia
[email protected]
Renewed interest in the thermal structure of the upper crust has
led to the development of a new generation of tools capable of
ASEG-PESA 2010 Conference Handbook
Abstracts
Here we demonstrate the application of the StGermain/
Underworld geodynamic modelling framework to basin-scale
geodynamic problems. The default code has been modified to
incorporate importing of geometrically complex geological
units, each with its own conductivity and heat production, and
temperature-dependent thermal conductivity. Thermal models
demonstrate the importance of incorporating 2 & 3D
geometries, with large lateral variations in the subsurface
temperature field and heat flow as a result of the heterogenous
basin architecture.
We explore the effect of lithological resolution, and identify a
critical level of detail required to adequately represent basinscale temperature variations. The regional temperature field play
a dominant role in determining tenement-level subsurface
temperatures, and highlight the importance of understanding
regional temperature variations in geothermal exploration.
3D THERMAL MODELLING VERSUS DOWN-HOLE
TEMPERATURE EXTRAPOLATION IN THE SYDNEYGUNNEDAH-BOWEN BASIN AND THE IMPLICATIONS
FOR TARGETING POTENTIAL GEOTHERMAL
ANOMALIES
Cara Danis* and Craig O’Neill
GEMOC, Macquarie University, Sydney, NSW, Australia
[email protected]
The Sydney-Gunnedah-Bowen Basins constitute the largest
sedimentary basin system of the East Coast of Australia and are
an important economic resource. Much attention has been given
on coal and natural gas development, but recently there has
been focus on the system’s thermal structure. Our previous
studies on the thermal structure of the Gunnedah Basin have
found basin architecture and insulating sediments have a
profound impact on the thermal structure. Heat refracts around
insulating coal & sediment layers, into adjacent zones of lower
thermal resistance, resulting in large lateral variations of the
subsurface temperature field. Current extrapolations of nonequilibrated down-hole temperature from shallow boreholes to
5 km depth, using shallow geothermal gradients, fail to account
for lateral variation in geology and thermal conductivity. Such
extrapolations may differ significantly to actual temperatures at
depth, due to lateral heat transfer effects, and data quality, and
may result in false peaks and target anomalies. 3D thermal
modelling provides more representative analysis of the thermal
structure at depth in the Sydney-Gunnedah-Bowen Basin
system with the ability to set model parameters for lateral
geological variation. With this geological and thermal
information embedded into the model the resulting thermal
structure maps at depth have greater accuracy and provide
a much better picture of the overall thermal structure of the
basin. This has significant implications for targeting potential
geothermal anomalies, as the derived temperature structure at
depth, and anomaly location, may vary significantly between
the two methods.
ASEG-PESA 2010 Conference Handbook
Day 2 Session 1 Stream 4
3D TECHNOLOGIES IN OFF-SHORE BASINS
KEYNOTE ADDRESS: NOVEL ADVANCES
IN SIMULTANEOUS SOURCE ACQUISITION
AND PROCESSING
Ian Moore
WesternGeco, Perth, WA, Australia
[email protected]
Until recently, seismic data acquisition has been fundamentally
limited by the requirement that the delay time between one shot
and the next be sufficient to avoid significant contamination of
data from one shot with energy from another. Acquisition with
simultaneous sources drops this requirement, and therefore
provides potential for enormous improvements in acquisition
rates and source sampling. In order to realise this potential
however, the way we acquire and process data must change.
The simplest way to process simultaneous source data is by
separating the sources at an early stage, such that conventional
processing can then be used. Synthetic and real data examples
illustrate that separation is viable in many circumstances,
especially when use is made of transforms that allow a sparse
representation of those data. Shot-dithering techniques, which
make the energy from one source appear incoherent in some
domain, are also important enablers for source separation.
Key applications of simultaneous source acquisition and
processing are illustrated with examples. These include the use
of simultaneous sources to improve inline shot sampling, and to
make the acquisition of wide-azimuth and undershoot data more
efficient. Provided the survey is properly designed, simultaneous
sources are shown to be viable both as a means to improve data
quality, and as a means to reduce the acquisition costs.
Most simultaneous source datasets acquired to date fire only two
sources simultaneously. Practical issues aside, it is shown that
there are benefits to increasing this number significantly, and the
future of simultaneous source acquisition probably lies in this
direction.
A MULTI-COMPONENT SEISMIC AZIMUTHAL
IMAGING TRIAL: PRELIMINARY RESULTS
Shaun Strong1,2* and Steve Hearn1,2
Pty Ltd, Sumner Park, QLD, Australia
2University of Queensland, QLD, Australia
1Velseis
[email protected]
In conventional (P) seismic-reflection surveys, a P-wave
generated at the surface is reflected to provide an image of the
subsurface. Upon reflection some of the energy is converted
into a shear (S) wave. This reflection is known as a converted
AUGUST 2010
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ABSTRACTS
modelling the 3D heat conduction problem, incorporating the
complex geology and physical properties of the crust. The
numerical and resolution requirements of such models has
necessitated a high-performance performance computing
approach, utilising massively parallel machine architecture to
obtain ~10 m resolution of models over a basin-scale.
Abstracts
ABSTRACTS
wave or PS-wave, and may improve the geological
interpretation. Velseis has acquired a number of 2D PS-wave
surveys at the shallow coal-scale (0–400 m). Typically, the two
images created from positive, and negative, offset rays can lead
to differing geological interpretation. The effect has also been
documented at the petroleum scale, and may be caused by
diodic-illumination and azimuthal anisotropy. This effect is
expected to be exacerbated in the 3D case.
To investigate these complexities we have recently acquired
a small trial 3D PS-wave survey with the immediate aim of
examining such azimuthal effects in detail. The ultimate aim is
a commercially viable 3D-3C methodology for coal-scale
targets. The trial dataset consists of an approximately
1000 m × 300 m swath, collected over a target that has previously
been investigated with a conventional 2D survey. The geological
environment consists of a target coal-seam with a depth ranging
from 70–120 m, and including significant faulting. The acquired
3D-3C survey has high shot density, compared to conventional
single-component data. This will allow us to produce four
full-fold datasets constructed using different azimuth rays. This
will be used to examine the effects of anisotropy and diodicillumination. We are simultaneously examining the P-wave
sections to determine if these are also affected by anisotropic
problems. The preliminary results from this investigation will be
presented.
3-D TOMOGRAPHIC Q INVERSION
FOR COMPENSATING ATTENUATION ANOMALIES
Kefeng Xin and Barry Hung*
CGGVeritas, Singapore
[email protected]
The propagation of seismic wave through viscoacoustic media
is affected by the attenuation that is caused by the quality factor
Q, resulting in significant loss of signal strength and bandwidth.
Gas trapped in sediment is an example of such media. Seismic
images of geological structures underneath shallow gas often
suffer from resolution degradation and the effect of amplitude
dimming, making the identification and interpretation of the
structures difficult. This in turn affects the ability to accurately
predict the reservoir properties. Thus, there is a need to
compensate the attenuation anomalies due to Q.
In this paper, we present a workflow of Q estimation
and compensation that is based on our previous work on
amplitude tomography. Our new approach involves utilizing
tomographic inversion for estimating Q from prestack depth
migrated common image gathers that fully honours the
wavepaths. By filtering the seismic data into different
frequency bands and measuring the effect of attenuation on
amplitudes in each band, the frequency dependent effect,
which was ignored in our previous amplitude tomography
work, of attenuation is fully taken into account, thereby
allowing Q to be estimated from our tomographic method.
By using the estimated Q volume in one of the migration
methods that incorporates Q in the traveltime computation,
we demonstrate, through real-data examples, that our
workflow provides an optimal compensation solution that
resolves amplitude, phase and bandwidth distortions due to
seismic attenuation.
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VALUE-ADD AND SAFE DRILLING FROM 4D AVO
EVALUATION IN THE ENFIELD OIL FIELD
Peter Thomas* and Megan Smith
Woodside Energy Ltd., Perth, WA, Australia
[email protected]
The Enfield oil field, on Australia’s Greater North-West Shelf,
started production in July 2006, and has already seen significant
benefit from 4D seismic monitoring. The technique is
particularly applicable in Enfield due to faulting and baffles
within the reservoir, the need for multiple water injection wells,
and the presence of a gas cap. Full-field monitor surveys in
February 2007 and December 2008 have made major
contributions to reservoir management and identification
of infill drilling opportunities.
This paper highlights the 2009 development drilling in the
field’s Sliver Block, where 4D not only supported the business
case for a new production and water injection well, but also
provided important information to enhance safe and efficient
drilling. 4D AVO analysis involved extraction of changes over
various source-receiver offset ranges, driven by a rock property
model in which nears and mids tend to show pressure changes,
while fars and ultra-fars show saturation changes.
A clear 4D AVO signal on the early monitor showed the
drilling target area to be pressured up by a distant injector,
contrary to pre-4D expectations. The later monitor confirmed
this, and also showed the oil target intact – with no significant
water sweep. Using 4D, significant overpressure in the target
was predicted. Accordingly, casing schemes for the wells were
redesigned to enable safe reservoir entry; the distant water
injector was shut in prior to drilling; and appropriate heavy
brine was ordered for completion operations. Actual pressures
fell within the predicted range, and a safe and successful
drilling campaign was achieved.
11:00–12:30
Day 2 Session 2 Stream 1
INNOVATIONS IN GEOPHYSICAL INVERSION
THE ROLE OF GEOLOGICAL UNCERTAINTY
IN DEVELOPING COMBINED GEOLOGICAL
AND POTENTIAL INVERSIONS
Laurent Ailleres1*, Mark Lindsay1, Mark Jessell2 and Eric de Kemp3
of Geosciences, Monash University, VIC, Australia
2IRD, Universite Toulouse 3, France
3Geological Commission, Toronto, ON, Canada
1School
[email protected]
Recently, implicit model building techniques have been
developed and they, for example, use geo-statistical methods to
interpolate boundary orientations as a scalar field (Calcagno
et al., 2008). Boundaries are implicitly formulated as iso-values
of that field. Using more than one potential allows modelling
for intrusion and unconformities. This technique is attractive
because it makes 3D geological modeling a repeatable task
and model uncertainty can be estimated from the geostatistical
estimators. However, this uncertainty does not take into account
the potential initial error on field measurements. It does not take
into account possible variation in the knowledge based
ASEG-PESA 2010 Conference Handbook
Abstracts
To assess the models against the initial geological data input,
we are going to develop geological objective functions based on
(e.g.) locations and gradients of boundaries. It is our intent to
combine these objectives functions with classical geophysical
objective functions to provide a new method for combined
geological and potential field inversions.
SOME COMMENTS ON THE INVERSION OF MULTISCALE EDGES TO CREATE GEOLOGICAL STRUCTURE
Philip Heath
PIRSA, Adelaide, SA, Australia
[email protected]
By taking the formulae used to create the gravitational and
magnetic response of a dipping contact, it is possible to derive
formulae dictating the points of maximum slope on a
corresponding gravity or magnetic profile. If then a series of
multi-scale edge points are determined from some gravity or
magnetic survey it should be possible to determine the physical
properties of the body using some type of inversion routine. In
order to resolve depth to the top of the body, thickness of the
body, slope of the contact and lateral position of the body, four
simultaneous equations are needed. The four equations arrive
from various upward continued levels of data. Due to the
relatively low number of solutions for the simultaneous
equations a Monte-Carlo style of inversion is used. It is not
possible to determine the density contrast (or magnetic
susceptibility contrast) using this technique. Three-dimensional
models of the Kalinjala and Karari Shear zones (in South
Australia) are shown.
The equivalence of direct forward modelling of a dipping
contact is discussed and the author concludes that despite this
equivalence multi-scale edge detection has its uses, notably for
locating subtle gravity and magnetic features, and detecting
regional structural trends.
GENERATING A RESOURCE ESTIMATE BY MAGNETIC
FIELD INVERSION – A STUDY OF THE HAWSONS
MAGNETITE DEPOSIT, NSW
Clive Foss1, John Donohue2, Doug Brewster2 and Nick Sheard2
1CSIRO Earth Science and Resource Engineering, North Ryde, NSW,
Australia
2Carpentaria Exploration, Brisbane, QLD, Australia
[email protected]
Resource definitions have regulatory requirements of sampling
from drilling. Drilling provides direct and precise measurement
of ore grades and characteristics which determine the financial
viability of the resource, but close drilling of a resource is very
expensive. Magnetic field inversion is an indirect method of
ASEG-PESA 2010 Conference Handbook
estimating ore grades and volumes. It is generally only assigned
an exploration role to make the resource discovery and design
the initial drilling program. However, in favourable circumstances
a combination of limited infill drilling and bulk sampling
by magnetic field inversion may provide a cost effective
and superior means of defining the resource. We illustrate
this with a study of the Hawsons magnetite deposit south of
Broken Hill.
The Hawsons magnetite deposit is a folded, bedded
Neoproterozoic (Braemar) iron formation that is well expressed
in regional (100 metre line spaced) aeromagnetic data. An initial
inversion of this magnetic anomaly provided a 3 dimensional
model of the envelope of the resource which is in good
agreement with initial drilling results. The task of defining
the resource is primarily to integrate the tonnage of ore at
a specified cut-off grade and to determine its value and the cost
of extraction, processing and shipping. The deposit is not a
single homogeneous unit, but rather a series of adjacent units of
different grade and thickness. Enhanced magnetic field imagery
reveals that there is limited structural disruption of the units but
that there are lateral variations of magnetization within the
structure which most probably express local variation in ore
grade and/or thickness. The more substantial of these variations
are addressed by details of the initial inversion model, but that
model provides insufficient resolution of the ore bands. Also,
and most importantly the model is a geophysical model of the
distribution of apparent magnetic susceptibility, rather than a
geological model of ore grade.
The spatial resolution of the shallow structure in the magnetic
field inversion has been enhanced by inverting the vertical
derivative of TMI, and further spatial resolution improvements
are being achieved through measurement of the magnetic field
at ground level. The transformation from apparent magnetic
susceptibility to a virtual ore grade poses substantial problems.
The high magnetic susceptibilities require that selfdemagnetization effects be included in the modelling. There is
no evidence that the magnetization direction is rotated by any
remanent magnetization oblique to the present field direction,
as confirmed by the close spatial fit of the model to the
intersected magnetite. This is consistent with the generally
coarse grained texture of the magnetite which is not suitable
for retaining an ancient magnetization. Nevertheless the
magnetite is still expected to carry a soft remanence acquired
in the ambient field which will cause discrepancies between
the apparent susceptibility derived from the inversion and
susceptibility measurements. To resolve these discrepancies we
are performing a series of palaeomagnetic and rock magnetic
studies which will establish proven relationships between ore
grade and magnetization. We are also currently combining the
initial inversion model with calibration details from the drilling
so as to use the geophysical inversion to extrapolate the
drilling results. This upgraded and transformed model will
provide predictions of intersection results for the next round
of drilling. We will first test the model against those new
drillhole results and then update the model again using the new
drillhole data as further constraints for the next inversion. In
this iterative process we hope to prove with each testing of the
model that we have combined the inversion model and drilling
results to prove the resource with sparser infill drilling than
would otherwise be required. With each drillhole we will also
grow the database of rock property measurements which are
key to translating between geophysical inversions and ore
grade geological models. In order to further improve spatial
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ABSTRACTS
information which is very often interpretative such as structural
evolution history, fault network and overprinting relationships
with themselves and the different formations. We present an
innovative method that will simulate numerous (millions)
geological models from a single initial structural dataset, taking
into account these variables. The models are then assessed
against potential inversions and modified to better fit potential
data. In the end, the models that both better fit geological input
data and potential field data will be retained. A best probable
model will be proposed that will satisfy geophysical data as well
as geological data.
Abstracts
resolution of the model we are also currently researching the
design and future deployment of novel down-hole magnetic
field sensors to augment the above-surface magnetic field
measurements.
Day 2 Session 2 Stream 2
PRELIMINARY INVESTIGATIONS USING A HELICOPTER
TIME-DOMAIN SYSTEM FOR BATHYMETRIC
MEASUREMENTS IN SHALLOW COASTAL WATERS –
PORT LINCOLN AND BROKEN BAY, AUSTRALIA
Julian Vrbancich
DSTO, Australian Technology Park, Eveleigh, NSW, Australia
[email protected]
TECHNOLOGY ADVANCES
DELINEATING LAKE BOTTOM STRUCTURE
BY TEM ON WATER SURFACE
Chow-Son Chen
Institution of Geophysics, National Central University, Taiwan
ABSTRACTS
[email protected]
Mapping water-bottom features involves in the fields of
environmental geophysics and engineering structural study. TEM
(Transient Electromagnetic) resistivity sounding is widely used
to map subsurface structures on land, but it is seldom used to
map underwater structures. Typically the geoelectrical resistivity
profile obtained on a water surface is affected by the
conductivity of a silty/clayey sediment blanket covering on a
water bottom; thus both detection and resolution of water bottom
stratigraphy decrease with depth. Recently the development of
TEM provides higher resolution and greater exploration depth
than ever before and it is time to consider whether this advanced
TEM technique can be applied to under-water mapping.
About 250 TEM soundings have been measured within a pond
of about 120 m by 60 m in a muddy deposits environments in
Southern Taiwan. For the TEM measurements the terrTEM unit
(Monex GeoScope) was used in an in-loop configuration and the
receiver spacing is about 5 m being located at the centre part of
transmitter loop, which is about the same size as the pond. For
imaging the vertical and horizontal resistivity distribution within
the deposit and the surrounding area, all sounding results were
interpreted using a smooth inverse procedure. Some auger
drilling and sounding were available for correlation. This led
to a final model. The lake water (resistivity around 4 ohm-m)
extends from water surface to a depth of 1m. Underneath the
water bottom is clay with a thickness greater than 30 m and
resistivity ranging from 1 to 5 ohm-m. The depth of the clayey
layer predicted by TEM data is comparable to that of drilled
wells nearby, and the thickened layer is possible the cause of the
pond forming. The lowest layer is alternate of sandy and clayey
layers with a resistivity less than 20 ohm-m. The depth of this
layer is greater than 30 m and most likely associated with an
acquifer. Thus interpretation of lake-bottom stratigrphy from
TEM on water surface is possible.
We believe that the experiment introduced here has
demonstrated a powerful method that can improve depth
investigation underneath a water bottom. In addition, the
proposed technique can be extended to a non-destructive
underwater mapping stratigraphy in a greater depth of water area
(such as a water reservoir) where the explosive seismic method
is prohibited. The success of the method depends upon the
appropriate design of survey parameters. As demonstrated, this
new application is open to further refinement, both in
instruments and in survey techniques.
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Helicopter time-domain AEM is being investigated as a
technique for bathymetric mapping in shallow coastal waters.
Previous studies in Port Lincoln, South Australia, used a
floating AEM system with receiver and transmitter electronics
modules obtained from a commercial helicopter AEM system
(RepTEM, Geosolutions Pty Ltd) to provide an upper limit to
the expected bathymetric accuracy based on current technology
for AEM systems similar to RepTEM. The same survey lines
were flown with an airborne system (SeaTEM) on two separate
occasions. A comparison of the interpreted water depths
obtained from the airborne and floating systems is presented.
An empirical data correction method based on modeled and
observed EM responses over deep seawater at altitudes varying
between ~20 and 60 m can lead to improvements in interpreted
water depths. A rapid method of obtaining accurate seawater
conductivities for EM modeling used a conductivity probe that
was dipped by helicopter in shallow and deep waters. The
results of a full survey of selected areas in Broken Bay (NSW)
undertaken with the SeaTEM system is presented. These areas
include beaches, exposed reef and shallow waters overlying
paleovalleys covered by shallow and deep sediments. A marine
seismic reflection survey together with Vibrocore samples of
sediment in Broken Bay were used to provide an estimate of the
sediment thickness and resistivity of shallow sediments to assist
in the interpretation of the EM response. Interpreted water
depths and depths to bedrock from SeaTEM data are generally
in good agreement with known bathymetry and seismic
estimates of bedrock depths shallower than ~90 m in water
depths shallower than ~25–30 m.
HIGH-RESOLUTION HELICOPTER GEOPHYSICS
IN SUPPORT OF A DEFENCE ENGINEERING PROJECT
T. Jeffrey Gamey1*, L.P. Beard1, W.E. Doll1, J.R. Sheehan1, J. Norton1
and M. Siwiak2
1Battelle, Oakridge, USA
2AECOM
[email protected]
In October and November of 2008, Battelle and AECOM
conducted an extensive airborne project at an Australian RAAF
base in support of a base expansion project. The purpose was
to identify, document and if possible, mitigate potential sources
of groundwater contamination and related pathways. The two
boom-mounted airborne systems that were deployed were
designed for detection and mapping of shallow buried metals.
An area of 1740 ha was surveyed with a combination of
magnetic gradiometer and time-domain electromagnetic
induction. Approximately 1230 ha of this was flown at low
altitude (1–3 m) with a 16-sensor vertical gradient system
(VG-16). The remaining area was flown at higher altitudes
due to vegetative cover. Areas of special interest totaling
290 ha were followed up with an 8-receiver low altitude
electromagnetic survey (TEM-8). Ground follow-up with
excavation was then conducted on a selection of anomalies
to identify their causative sources.
ASEG-PESA 2010 Conference Handbook
Abstracts
Day 2 Session 2 Stream 3
GEOPHYSICS AND GEOTHERMAL APPLICATIONS
KEYNOTE ADDRESS: THE ENERGY PORTFOLIO
DOWNUNDER: WHAT’S NEW AND ENABLING?
Barry Goldstein
Director Petroleum & Geothermal, PIRSA, Adelaide, SA, Australia
[email protected]
Australia’s subsurface holds a huge energy resource endowment
including coal, petroleum, uranium, and geothermal energy.
Australia’s oceanic surrounds, sunshine and wind provide
additional options for energy supplies. That is fortunate and these
comparative advantages will enable Australia to sustain
prosperity with safe, secure and competitively priced energy
supplies in the face of increasing demand. Oil will peak – but we
are unlikely to see a peak in fuel for transport or power.
A portfolio of new energy plays and technologies in traditional
hunting grounds, and traditional energy plays in frontier settings
have and will attract investment. Growth plays are not limited to:
coal seam gas (CSG) to liquefied natural gas (LNG); Engineered
Geothermal Systems (EGS); underground coal gasification
(UCG); fractured shale plays; Precambrian sub-salt plays; deep
water petroleum; gas to synfuels; coal to synfuels, LNG for
transport; biofuels for transport; carbon capture and storage; solar
thermal technologies; ocean energy technologies; and more.
This presentation will draw attention in particular to the future
for geothermal energy and unconventional gas plays in South
Australia, but in a national and international context. It will also
touch on key principles for enabling and trustworthy legislation
and regulation for energy resource development.
In conclusion, risks in meeting future energy challenges will be
managed with a portfolio of engineered energy plays, including
innovative energy storage and efficiency; new fuels; new
transportation technologies; new modes of power generation,
augmented energy infrastructure and enhanced market rules.
Watch this space.
ASEG-PESA 2010 Conference Handbook
ZTEM AIRBORNE AFMAG EM RESULTS OVER
THE REESE RIVER GEOTHERMAL TEST AREA,
CENTRAL NEVADA
Jean M. Legault, P. Berardelli, M. Orta and B. Milicevic
Geotech Ltd., Aurora, ON, Canada
[email protected]
Geophysics and EM methods in particular have been used for
geothermal exploration for decades. Techniques such as DCResistivity, ground transient electromagnetic (TEM) sounding
and more recently magnetotelluric (MT) methods, are used to
map the geothermal source structures. These EM and electrical
methods are capable of providing good depths of investigation
and resolution but at a very high cost. ZTEM airborne AFMAG
(audio frequency electromagnetic) may provide a cost effective
method to map the electrical properties of the subsurface to
significant depth.
A ZTEM (Z-Tipper Axis Electromagnetic) airborne AFMAG
surveys was conducted over the Reese River Test Block,
situated in central Nevada in August, 2009. The Reese River
prospect is a “blind” geothermal resource that lack surface
characteristics such as hot springs. It has hosted a number of
geophysical surveys, including seismic, gravity, magnetotelluric
and radiometric surveys. The ground MT survey covered the
main areas of interest over the site and its purpose was to map
the smectite-zeolite zone which forms a low resistivity cap over
the outer margins of the higher resistive reservoir at depth. The
MT lines were overflown with ZTEM for the purposes of
comparison.
The ZTEM test results performed over the known geothermal
prospect in northern Nevada appear to correlate very well with
the magnetotelluric results and the known geology, in particular
the presence of both major and secondary fault structures and
geologic contacts. 2D inversions of the airborne ZTEM appear
to agree very well with the inversions obtained from ground
MT, except in areas of pronounced 3D behaviour, where the 2D
assumption is no longer valid.
MONITORING FLUID RESERVOIR IN AN ENHANCED
GEOTHERMAL SYSTEM USING MAGNETOTELLURICS
Stephan Thiel1*, Jared Peacock1, Graham Heinson1
and Louise McAllister2
1TRaX, School of Earth and Environmental Sciences, University
of Adelaide, SA, Australia
2Petratherm Ltd, Unley, SA, Australia
[email protected]
Geothermal exploration plays an increasing role worldwide and
in Australia in order to meet carbon emission targets and to
provide green and renewable energy alternatives to coal.
In Australia, EGS systems are widely used to extract geothermal
energy from the subsurface. Initially, the stimulation process
involves pumping large amount of fluids into the subsurface at
depths of reasonable temperature to ensure a maximum energy
output. The high-pressured fluids penetrate from the borehole into
the surrounding sedimentary rocks and increase the permeability
of the system until the stimulation is finished. Subsequently, a
second borehole is put in place to extract the heated fluids.
Magnetotelluric (MT) measurements will be undertaken at the
Paralana drill site in 2010, where the stimulation is conducted
by Petratherm. The measurements take place in three stages in
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ABSTRACTS
A combination of historical records, aerial photographs, GIS
and modern geophysics were combined to provide a unique
picture of the site prior to a new round of base expansion and
construction. Targets identified included both documented and
undocumented waste pits and trenches, gun emplacements,
buried planes, structural foundations, and naturally-occurring
magnetic rock and soils. The entire 1740 ha of VG and 290 ha
of EM were surveyed in less than 5 weeks at a resolution
approaching that of ground-based systems.
Abstracts
order to image the extent of the fluid body at depths of
3.5–4 km. To improve the outcome of the deployments, about 50
stations measure the MT response between periods of 100–0.01 s
prior to the stimulation to provide an initial model of the area.
This is then used to compare and constrain the responses
collected during and after the stimulation of the fluids
into the reservoir. The aim of the survey is to delineate the
extent of the water-filled reservoir.
During the stimulation, time-series of magnetic and electric field
changes will also be recorded for comparison with events from
the Micro Earthquake Array. These studies will look into the
seismoelectric effect associated with the seismic events during
the stimulation.
Day 2 Session 2 Stream 4
3D TECHNOLOGIES IN OFF-SHORE BASINS
ABSTRACTS
THE TUI 3D SEISMIC SURVEY, TARANAKI BASIN,
NEW ZEALAND: REPROCESSING 2009
Jim Montalbetti1*, Bala Kunjan2 and Andy Furniss2
Exploration Consultants, Avalon Beach, NSW, Australia
2Australian Worldwide Exploration, North Sydney, NSW, Australia
1Avalon
[email protected]
The first Tui 3D seismic survey was acquired one month after
the discovery of oil in the Paleocene age Kapuni Group
‘F Sand’ in February 2003. These data were used to plan the
follow-up drilling campaign, resulting in the discovery of the
Amokura and Pateke pools north of Tui in 2004. In 2005, an
extension 3D survey was acquired to the north of the original
survey, providing a total 3D coverage of 439 sq. km. Tui came
onstream in July 2007 and has produced over 25 mmbl oil to
date from total estimated recovery of 50 mmbl oil.
The reservoirs at Tui are at depths of 3600 m LAT, and lie on a
broad low relief structural nose extending north from the Maui
High. Imaging in depth is challenged by the relatively low
frequency content of seismic events at this depth, and by subtle
velocity variations in the overlying sequence.
In early 2009, Australian Worldwide Exploration (AWE), as
operator of the Tui field, conducted a review of the original 3D
data processing sequence and identified a number of additional
elements in the workflow that might, as a result of new
processing technology, lead to improvement in the data quality
of this 3D survey. AWE felt that an improved data set would aid
in further exploration and appraisal drilling by helping to mature
additional leads in the field.
Test reprocessing was carried out over a key 100 sq. km. area
of the field. Good results from this test led to a full reprocessing
of both the 2003 and 2005 data sets. This paper describes
the redesign of the 3D processing sequence and shows examples
of the improvements that were obtained using a current state of
the art workflow to reprocess the data set.
3D MAPPING AND GRAVITY MODELLING OF CAPEL
AND FAUST BASINS
Peter Petkovic*, R. Lane, N. Rollet and G. K. Nayak
Geoscience Australia, Canberra, ACT, Australia
The Capel and Faust basins lie at water depths of 1500–3000 m,
800 km east of Brisbane on the Lord Howe Rise. Geoscience
Australia began a petroleum prospectivity study of these remote
frontier basins with acquisition of 2D reflection and refraction
seismic, gravity, magnetic and multi-beam bathymetry data
across an area of 87 000 km2 during 2006/07. The approach
mapped a complex distribution of sub-basins through an
integration of traditional 2D reflection seismic interpretation
techniques with 3D mapping and gravity modelling. Forward
and inverse 3D gravity models were used to inform the ongoing
reflection seismic interpretation and test the identification of
basement. Gravity models had three sediment layers with
average densities inferred from refraction velocity modelling
of 1.85, 2.13, 2.31 t/m3 overlying a pre-rift basement of
density 2.54 t/m3, itself considered to consist in part of intruded
older basin material. Depth conversion of horizon travel times
was achieved using a quadratic function derived from raytracing forward models of refraction data. Gravity modelling of
the simple density model arising from the initial interpretation
of reflection seismic data indicated a first order agreement
between observed and calculated data. The second order misfits
could be accounted for by a combination of adjustments to the
density values assigned to each of the layers, localised
adjustments to the basin depths, and heterogeneity in the
basement density values. The study concluded that sediment
of average velocity 3500 m/s exceeds 6000 m thickness in the
northwest of the area, which is sufficient for potential petroleum
generation.
STRESS DEPENDENCY OF SHALE ELASTIC PROPERTIES:
MEASUREMENTS, MODELLING AND PREDICTION
Marina Pervukhina
CSIRO Petroleum, WA, Australia
[email protected]
Stress dependency of full elastic tensor of shales is very
important for seismic interpretation, overpressure prediction, 4D
monitoring, etc. In spite of the importance of the problem, there
is no conventional theory for transversely isotropic (TI) media
which allows describing stress dependency of shales with a
small number of physically plausible fitting parameters. Using
Sayers-Kachanov formalism, we develop a new stress sensitivity
theory for TI rock which predicts stress sensitivity behaviour of
all five elastic constants of TI medium. The theory is used to
build the models for about 50 shales on the basis of new
experimental results and data obtained from literature. The four
fitting parameters (namely, shear and normal compliances at
zero pressure, characteristic pressure, and pore orientation
anisotropy parameter) show obvious correlations with the depth
from which the shale is extracted. With increase of the depth,
the shear compliance decreases exponentially and the ratio of
normal to shear compliance increases linearly. The pore
orientation anisotropy parameter exponentially increases with the
depth for the most of the shales indicating that pores are getting
more aligned in the bedding plane. The characteristic pressure
shows no visible correlation with the extraction depth. The
suggested model allows predicting of stress dependency of all
five elastic constants if only two of them are known what can be
used for the reconstruction of all five elastic constants of shale
from log data. The model is also demonstrated to be useful for
seismic interpretation and 4D monitoring.
[email protected]
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ASEG-PESA 2010 Conference Handbook
13:30–15:00
Day 2 Session 3 Stream 1
INNOVATIONS IN GEOPHYSICAL INVERSION
A BRIEF ANALYSIS OF ZTEM DATA
Daniel Sattel1* and Scott Thomas2
1EM Solutions, Golden, Colorado, USA
2Condor Consulting Inc., Lakewood, Colorado, USA
[email protected]
The ZTEM system is an airborne AFMAG system, which
measures the EM response of the interaction between local
electrical heterogeneities and distant natural-field sources, such
as distant sferic activity. The delivered products are ZTEM
tipper profiles, which are the complex ratios of the vertical and
horizontal Fourier-transformed voltages in the frequency range
30–360 Hz.
An algorithm, written by Constable and Wannamaker, that
computes the magnetotelluric response of a 2-D earth was
modified to allow for the computation of ZTEM responses.
Taking into consideration the noise level of the ZTEM system,
the modified algorithm was used to predict the sensitivity of
ZTEM data to a discrete conductor in a range of host
environments.
The same algorithm was used to model ZTEM field data in an
area of existing airborne EM coverage. The latter allows for a
comparison between the resolution of active airborne EM
systems, such as VTEM, and the ZTEM system.
3D INVERSION OF ENTIRE AEM SURVEYS USING
A MOVING FOOTPRINT
Glenn A. Wilson*, Leif H. Cox and Michael S. Zhdanov
TechnoImaging LLC, Salt Lake City, Utah, USA
[email protected]
In mineral exploration, hydrological studies, and shallow water
bathymetry it is often convenient to perform 1D inversion of
TEM data. Although a uniqueness theorem exists for the special
case of mathematically perfect broadband data over a truly
layered Earth, in practice realisable TEM data do not fully
define the geoelectric section. Therefore, it is desirable to
constrain the inversion with all available information, in order
to define sub-surface conductivity as completely as possible.
Accordingly a program has been developed to perform
geologically-constrained 1D TEM inversion. Different types
of inversion are permitted: geometry inversion, homogeneous
property inversion, and heterogeneous unit inversion. During
geometry inversion, the layer boundaries are allowed to move,
except at fixed points, e.g. drilled contacts. During homogeneous
property (“stratigraphic”) inversion, the conductivity of each
geological unit is optimized, with each unit assumed uniform in
conductivity across the entire survey area. During heterogeneous
unit inversion, the conductivity is allowed to vary within each
geological unit, except where constrained by conductivity
measurements taken on drill core samples or downhole. The 1D
inversion is performed in a fully 3D context: a localized 1D
model is extracted and adjusted at each location in the survey
area. The method is illustrated on airborne TEM data recorded
over shallow coastal waters, constrained by sonar and by
conductivity measurements of seawater and sediment core.
Day 2 Session 3 Stream 2
TECHNOLOGY ADVANCES
AUTOMATED IDENTIFICATION OF PORPHYRY
MAGNETIC SIGNATURES
Eun-Jung Holden1, Shih Ching Fu1, Peter Kovesi1, Mike Dentith1,
Barry Bourne2 and Matthew Hope2
1Centre for Exploration Targeting, School of Earth &
Environment, University of Western Australia, WA, Australia
2Barrick Gold, Perth, WA, Australia
[email protected]
We show that it is practical to invert entire airborne
electromagnetic (AEM) surveys to 3D conductivity models with
hundreds of thousands of cells within a day on a workstation. We
have exploited the fact that the area of the footprint of an AEM
system is significantly smaller than the area of an AEM survey to
develop a robust 3D inversion method which uses a moving
footprint. Our implementation is based on the 3D integral
equation method for computing AEM data and sensitivities, and
the re-weighted regularized conjugate gradient method is used to
minimize the objective functional. Even for terranes which are
arguably as close to 1D as geologically possible, we demonstrate
that results from our 3D inversion are a significant improvement
over those models obtained from layered earth inversion. We
demonstrate this with 3D inversion of RESOLVE frequencydomain AEM data acquired for salinity mapping over the
Bookpurnong Irrigation District in South Australia.
GEOLOGICALLY-CONSTRAINED 1D TEM INVERSION
Peter Fullagar1*, Julian Vrbancich2 and Glenn Pears3
Geophysics Pty Ltd, Taringa, QLD, Australia
2DSTO, Australian Technology Park, Eveleigh, NSW, Australia
3Mira Geoscience Asia Pacific Pty Ltd
1Fullagar
[email protected]
ASEG-PESA 2010 Conference Handbook
Magnetic data are important in exploration for gold and other
hydrothermal deposits due to the relationship between
mineralisation and secondary magnetite abundance. In the
copper-gold rich porphyry environment large alteration systems
that can both create and destroy magnetite are commonly
recognized. These systems are characterized by concentric zones
with the central potassic alteration often associated with a
discrete sub-circular magnetic high or low dependent upon host
and emplacement depth. User-defined automated image analysis
methods can be applied to magnetic data to objectively and
efficiently locate and enhance signatures consistent with
copper-gold porphyry deposits.
A three step approach is taken to the identification of porphyry
signatures: a circular feature detection technique, namely the
radial symmetry transform; a boundary enhancement technique,
namely the magnetic contrast transform; and a feature boundary
detection technique using deformable splines. The radial
symmetry transform analyses the convergence and divergence
of image gradients to locate elevated and depressed circular
features. This transform allows the detection of features of
varying sizes and degrees of circularity. The magnetic contrast
transform then highlights the boundaries of features possessing
magnetic contrast from their surroundings. The boundaries of
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ABSTRACTS
Abstracts
Abstracts
these signatures are then traced by deformable splines which
iteratively converge onto the margin of the signature resulting
in an estimate of size and shape of the defined anomaly.
APPLICATION OF AUTOMATED DETECTION
TECHNIQUES IN MAGNETIC DATA FOR IDENTIFICATION
OF CU-AU PORPHYRIES
Matthew Hope
Barrick Gold, Perth, WA, Australia
ABSTRACTS
[email protected]
Through a joint research initiative between Barrick Gold and the
Centre of Exploration Targeting at the University of Western
Australia automated shape recognition technology has been
developed for application to porphyry copper gold exploration.
The result is the development of the porphyry texture filter for
application on magnetic datasets. Many mineralised porphyries
display concentric zonation in their magnetic character as a
by-product of their extensive hydrothermal alteration systems
and associated secondary magnetite development/destruction.
This characteristic magnetic signature has been exploited
through application of image processing techniques which enable
the enhancement, identification and quantification of features
which agree with a user defined set of criteria for size, shape
and magnetic contrast.
Development of the technique was carried out on the world class
Reko Diq porphyry system resulting in successful identification
of all major known mineralised systems and additional targets
within the camp. Significant user control over filter input
parameters has resulted in the ability to successfully apply the
filter on projects throughout South America, Papua New Guinea
and Eurasia in variable geological and erosional environments.
Results include clustering and prospective camp definition on
the regional scale and generation of subtle anomalous zones
within predefined prospective camps that may not have been
targeted in the absence of filter results.
The ability to rapidly characterise porphyry-like signatures using
approach based on mathematical principles and geometries
results in an unbiased target layer. When integrated with other
geoscientific data application of the filter has consistently led to
target generation.
APPLICATION OF POISSON’S RELATIONSHIP
TO GEOLOGICAL INTERPRETATION OF GRAVITY
AND MAGNETIC FIELD DATA
Clive Foss
CSIRO, North Ryde, NSW, Australia
[email protected]
Poisson’s relationship allows us to estimate the ratio of
anomalous density to anomalous magnetic susceptibility
from coincident gravity and magnetic field expressions
of a single geological body. At regional scales modelling
of gravity and magnetic fields provides upper bounds
on anomalous density and magnetic susceptibility values of
bodies which have an expression in one field and not the other.
At more local scales relationships may be more readily
established between magnetic fields and the vertical gradient of
gravity fields. Modelling of high-resolution magnetic field data
which is widely available across Australia allows the Poisson
relationship to be exploited to evaluate the possible contribution
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AUGUST 2010
of gravity and airborne gravity gradiometry surveys to
exploration programs, particularly in exploration for IOCG
deposits. However, for deep, compact sources there is limited
sensitivity in de-coupling absolute values of volume and density
and magnetization contrasts. In favourable circumstances
Poisson’s relationship can also be used to estimate rotation of
the resultant (induced plus remanent) magnetization from
displacement of gravity and magnetic anomalies, or conversely
to place bounds on that rotation from proximity of the
anomalies. This paper illustrates geological interpretation
applications of the above issues using synthetic model studies
and some Australian field examples.
Day 2 Session 3 Stream 3
ENGINEERING APPLICATIONS FOR GEOPHYSICS
ENGINEERING GEOPHYSICS IN CHINA
Zhao Yonggui
Institute of Geology and Geophysics, ACS, Beijing, China
[email protected]
In recent years the great progress has been made in Chinese
engineering geophysics, so as in the ability resolving of the
complexity engineering problems, the development of new
techniques, and the manufacture of new instrument and
equipment, following the national construction development.
Charactering with high resolution and high reliability,
engineering geophysics is serving to engineering exploration,
engineering quality detecting, disease diagnose and treatment
for railway, highway, water resources and hydropower, mining
and urbanization construction programs.
The kinds of engineering geophysics methods used in China
include the elastic wave, electromagnetic wave, electromagnetic
inductive method and electrostatic field method. The mainly
methods used in engineering are seismic, sonic and ultrasonic
technique, GPR and ERT.
The research of new method has gotten much progress in the
aspects of interpretation theory, data processing technique and
specialization technology. The remarkable new technology are
scattering imaging and 2D time-frequency analysis methods.
The scattering imaging is suitable for prospecting of complex
structure with higher resolution than reflection. The 2D
time-frequency analysis technology makes fully use of the
information in time domain and transient spectrum, and
greatly promoted the interpretation level of geophysical
signals.
The TST (Tunnel Seismic Tomography) technique is the most
remarkable new technology for tunnel geological prediction
based on scattering imaging method. It successfully resolves the
problems, how to distinguish the individual wave coming from
different orientation and to filter some of them in 3-D field,
and how to determine the velocity distribution ahead the tunnel
face.
Besides that, there are also other technology remarkable,
so as SSP (Seismic Scattering Profile) for complex geological
structure exploration with higher resolution than reflection
technique, and BCT (Bridge CT) based on sonic tomography
for concrete bridge detecting.
ASEG-PESA 2010 Conference Handbook
Abstracts
Robert J. Whiteley
Coffey Geotechnics, NSW, Australia
[email protected]
Annually, Australian’s generate more than 1.6T of solid waste
from commercial, industrial and municipal sources. Even with
improved waste recycling practices, 71% of this waste is
deposited in the 650 registered landfills located throughout urban
and rural Australia. Operating under strict environmental
guidelines, such landfills will continue to provide optimal
solutions for residual waste disposal at most locations in
Australia for many years.
Over the last 30 years an expanding regulatory regime and
improving landfill management practices have seen
increased application of geophysics at Australian landfills,
mainly for waste and site characterisation, groundwater
and contamination mapping and, more recently, for waste
treatment monitoring, post-closure rehabilitation and
environmental monitoring.
Case studies demonstrate the application of geophysics at a
number of Australian landfills. At Wollongong, borehole seismic
imaging was used to define the base and margins of a capped,
slag landfill in an old quarry for multi-story residential
development. In western Sydney, high-res magnetics located
ferrous objects in an extensive area of uncontrolled clayey fill in
a former gravel quarry that was to be dynamically compacted
prior to release as residential land. On Norfolk Island, gravity
estimated the volume of waste-rock fill in an infilled valley and
resistivity imaging located the fill base and near-surface boulders
for removal. At a large industrial site in Queensland,
electromagnetic profiling defined the margins of a capped
landfill, located shallow trenches containing metallic waste and
offsite leachate migration. Again in Sydney, advanced MASW
testing monitored the effectiveness of dynamic compaction of
uncontrolled, rock-waste fill.
MAPPING POLLUTION AND COASTAL HYDROGEOLOGY
WITH HELICOPTERBORNE TRANSIENT
ELECTROMAGNETIC MEASUREMENTS
Niels B. Christensen1* and Max Halkjaer2
1Department of Earth Sciences, Aarhus University, Denmark
2SkyTEM ApS, Denmark
[email protected]
Coastal hydrology is becoming the focus of increasing interest
for several reasons. Hydrogeological models need good
boundary conditions at the coast line, and with the expected sea
level rise due to climate changes, it becomes increasingly
important to grasp the dynamics of coastal hydrology in order to
predict the consequences of sea level rise for nature and society.
We present a helicopterborne transient electromagnetic survey
from a region at the North Sea coast in western Jutland,
Denmark, carried out with the purpose of mapping the coastal
hydrogeology at a seriously polluted site to assist in the
assessment of the extent of the pollution and to provide data
for remediation activities. Twenty-six lines with a length of
~2 km and a line spacing of 50 m cover the coastal zone. Data
are subjected to constrained inversion with one-dimensional
multi-layer (smooth) models. The results are presented as
ASEG-PESA 2010 Conference Handbook
model sections and as maps of mean conductivity in elevation
intervals. The survey results are basically in accordance with
results from other investigations as far as the extent of the
pollution plume is concerned, but also point to hitherto
unknown directions of seepage. The interleaving of fresh water
extending offshore under the shallow sea and the salt water
infiltrating under the onshore fresh water aquifer can be clearly
discerned and reveals preferential flow channels.
Day 2 Session 3 Stream 4
MINERALS DISCOVERY
COMPARISON OF DIGHEM EM AND MAGNETIC
RESULTS FOR DETECTING EPITHERMAL AND SHEAR
ZONE GOLD DEPOSITS
Mohsen Shademan1*, Gholam H Noroozi1 and AliReza Arab Amiri2
of Mine Exploration, Tehran University, Iran
2Department of Geophysics, Shahrood Technology University, Iran
1Department
[email protected]
High resolution Dighem data over broad areas have been found
to optimize exploration for gold deposits in different geological
environments. Dighem, simultaneously investigate four different
data include EM data with five frequency, magnetic
susceptibility, gamma ray spectrum for radio elements and
altitude. These data have been provided for some part of Iran by
Fugro Corporation in early years for exploring mineral deposits.
Because of the small flight line spacing at the case study region,
Alut, the magnetic data are interpreted for mineral and structural
exploration by the output of Model Vision and Quik Mag
programs. Furthermore the HEM data are processed by Emflow
and Siemon algorithms for producing sections. Then the results
of Magnetic and electromagnetic data are discussed and
compared with each other in order to define the exact anomaly
place(s) for two different kind of gold deposits with respect to
prior information like geological information. We try this for
discussing the ability of HEM data and its inversion algorithms
for detecting the small veins of mesothermal gold deposits.
STRUCTURE AND MINERALISATION MAPPING
USING BOREHOLE RADAR AT CHARTERS
TOWERS GOLD MINE; SUCCESSES, FAILURES
AND WHERE TO NEXT?
Carina Kemp1*, Sara Warren2 and Rebecca Williams2
Pty Ltd, Eveleigh, NSW, Australia
2Citigold Corporation Ltd, QLD, Australia
1GeoMole
[email protected]
This paper will present the results from borehole radar trials at
Citigold’s Charters Towers Gold Mine. The borehole radar trials
were done in 15 drillholes and surveying was conducted over
three separate acquisition periods between August 2007 and
December 2008. Dielectric property measurements were also
conducted on a variety of samples relative to the mineralization
and host rocks.
The initial aims of the surveys were to determine the ability
of borehole radar to map complex structures and splays off the
main Warrier Shear. Results from the first acquisition trial were
promising with clear reflections from basalt dykes and the main
structure. Variations in the amplitude of reflections from the
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ABSTRACTS
GEOPHYSICS AT AUSTRALIAN LANDFILLS: CASE
STUDIES
Abstracts
shear were interpreted to be from changes in the dielectric
of the actual shear zone. Dielectic tests shows that there was a
markable difference between the dielectric constant measured for
massive pyrite with Gold present compared to non-mineralised
shear zones. This lead to the hypothesis that the amplitude of
the borehole radar reflections could be analysed to determine the
locations along these reflections from massive pyrite and hence
gold mineralization.
The second and third field trials involved the surveying of over
8 drillholes that were drilled mostly from surface sub-parrallel to
the main ore zone. The data was interpreted for high amplitude
reflections and multiple targets were identified. Seven of these
targets have no been drilled with a 60 percent hit rate on good
gold grade. Modelling and further analysis of the data is now
being conducted to determine what these results mean for the
mine and for the future use of borehole radar at Charters Towers.
THE POWER OF FREQUENCY DOMAIN EM: PRINCIPLES
AND CASE HISTORIES
Greg Hodges*, Dima Amine and Greg Paleolog
Fugro Airborne Surveys, Mississauga, Ontario, Canada
ABSTRACTS
[email protected]
Unique features of Frequency Domain EM (FDEM) systems are
the high frequency, the measured in-phase component, multiple
tuned (narrow band) frequencies, and multiple-component
transmitters. The high frequencies give FDEM high sensitivity
to weak conductors and thin layers, and provide for conductivity
mapping in highly resistive areas. The in-phase measurement
extends the conductor sensitivity to the inductive limit and
provides phase-angle measurements for accurate conductivity
determination. The combination of these two features gives
FDEM the maximum geological bandwidth available from any
airborne EM system. The frequency-tuning gives excellent
rejection of power line and other external noise. The horizontal
dipole (vertical coaxial coil) transmitters, unique in airborne EM
systems, are maximum coupled to vertical and linear conductors,
and minimum-coupled to the host geology, providing the best
signal-to-geological-noise sensitivity for discrete conductor
targets, and the highest spatial resolution possible from the air.
These features are illustrated through examples of applications.
Kimberlite detection and geological mapping in Archean cratons
require accurate measurements in resistive geology. Sensitivity
to extreme conductivity is necessary for nickel-sulphide target
detection, and some application in mapping brine plumes.
Surveys mapping ground conductivity in large urban
environments and under active power lines demonstrate the very
high noise rejection capable with tuned circuits. High nearsurface resolution is demonstrated by dry-land salinity surveys,
bathymetry and sub-bottom examinations.
15:30–17:30
Day 2 Session 4 Stream 1
INNOVATIONS IN GEOPHYSICAL INVERSION
IMPROVED IMAGING OF THE SUBSURFACE USING A
GRAVITY AND MAGNETOTELLURIC JOINT INVERSION
Rachel Maier1*, Graham Heinson1, Mark Tingay2 and Stewart
Greenhalgh3
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1The
University of Adelaide, SA, Australia
University, Bentley, WA, Australia
3ETH Zurich (Swiss Federal Institute of Technology)
2Curtin
[email protected]
We present a newly developed 2D magnetotelluric (MT) and
gravity petrophysical joint inversion. Single inversions of MT and
gravity can produce non-unique and ambiguous models that fit
the observed data equally well. Conventional methods to reduce
such non-uniqueness is to introduce external constraints, such as
geological predigest or inverting for a specific model type. An
MT and gravity joint inversion helps to reduce model ambiguity
without requiring these additional external constraints.
Joint inversions take two geophysical data sets, measured over
the same subsurface geology and simultaneously invert them
to produce an integrated model. To do this a link is required
between the different data sets. In a sedimentary environment
Archie’s Law and the porosity-density relationship describe
the dependency of conductivity and density on porosity.
Consequently, porosity provides the crucial link. Traditional
petrophysical joint inversions would generate both a resistivity
and density model and use an equation to link them. However,
our joint inversion inverts directly for porosity since both
conductivity and density are dependent on porosity. The
inversion produces a single porosity model that is constrained
by both MT and gravity data.
Synthetic model testing demonstrates our joint inversion
produces a more accurate representation of subsurface than
achieved by an MT or gravity inversion alone. The joint
inversion improves the sharpness of boundaries and accuracy of
reconstructing the original subsurface values. It has been applied
to the Renmark Trough in South Australia and the San Diego
Trough, located offshore from California. These case studies
confirmed the synthetic testing results.
STRUCTURALLY BASED JOINT INVERSION
OF ELECTROMAGNETIC, SEISMIC AND POTENTIAL
FIELD DATA FOR IMPROVED CLASSIFICATION
AND CHARACTERIZATION: FIELD EXAMPLES FROM
THE VADOSE ZONE TO MANTLE DEPTHS
Luis A. Gallardo1*, Max Meju2, Juan C. Montalvo-Arrieta3 and Rogelio
Vazquez-Gonzalez4
1School of Earth and Environment, University of Western
Australia, WA, Australia
2Lancaster Environmental Centre, Lancaster University, United
Kingdom
3Facultad de Ciencias de la Tierra, Universidad Autonoma de
Nuevo Leon, Mexico
4Division de Ciencias de la Tierra, CICESE, Mexico
[email protected]
Accurate characterization of mineral and fluid heterogeneity
in subsurface material and its influence on fluid flow or storage
in subterranean reservoirs is of crucial importance in a wide
range of contemporary issues including the use of mineral
and ground water resources, volcano monitoring, carbon dioxide
sequestration and efficient extraction of fossil fuels. A key
strategy to characterize subsurface materials is the integrative
analysis of tomographic maps of several physical properties
provided by different geophysical data. Among the recent
strategies to produce these tomographic maps is the joint
inversion. Unfortunately, most joint inversion techniques are
based on hypothetical property relationships that hinder the
ASEG-PESA 2010 Conference Handbook
Abstracts
site-specific property correlations that characterize individual
materials. Differently, a recently developed cross-gradient joint
inversion technique is underpinned by the hypothesis of
structural resemblance and permits the coexistence of natural
property correlations that provide the key to reveal the signatures
of subsurface materials. In the present work, electromagnetic,
seismic and potential field data are jointly inverted for several
field sites with near surface targets. The results show not only a
clearer disposition of the mapped units in structural terms, but
also a sound evidence of their actual fluid-mineral characteristics.
In general, the results demonstrate the power of analyzing
multiple-property images when they are structurally consistent.
INCREASED ACCURACY IN MINERAL AND
HYDROGEOPHYSICAL MODELLING OF AEM DATA
VIA DETAILED DESCRIPTION OF SYSTEM TRANSFER
FUNCTION AND CONSTRAINED INVERSION
is tested and verified on synthetic examples with and without
noise. This technique is also successfully applied to four real
data sets for mineral exploration, and it is found that the
estimated depths and the associated model parameters are in
good agreement with the actual values.
Day 2 Session 4 Stream 2
PNG EXPLORATION
KEYNOTE ADDRESS: SCIENCE REVEALS HIDDEN
WEALTH IN PNG
Ian Longley
General Manager Exploration, Oil Search Limited, Sydney, NSW,
Australia
Andreas Viezzoli1*, Esben Auken2 and Anders Christensen2
Geophysics ApS, Denmark
2Department of Earth Sciences, Aarhus University, Denmark
1Aarhus
This paper aims at providing more insight into the effect that
inappropriate modeling of the different components of the
system transfer function of airborne TEM systems have on the
models recovered when inverting HTEM data. For this purpose
we use synthetic data, and analyze these effects both in data and
in model space. The parameters taken into account are: the low
pass filters present in any system, the shape of turn on and turn
off, the number of waveform repetition, the Tx-Rx altitude, the
Tx-Rx timing, i.e., the gate timing, etc. Low pass filters, shape
of turn off, Tx-Rx altitude, and Tx-Rx timing affect mainly the
shallow to intermediate part of the model, whereas the waveform
repetition and shape of turn on the deeper part. Results show
that, in order to recover the true model, all these parameters
need to be taken into account and modelled correctly during
inversion of HTEM data. This holds both for exploration and
hydrogeophysical applications. We then present an application
of this approach on real VTEM data from an exploration
survey. The results from constrained inversion of the VTEM,
compared with borehole information and with other modeling
methodologies, show its validity.
A GENERALIZED ALGORITHM FOR GRAVITY
OR SELF-POTENTIAL DATA INVERSION WITH
APPLICATION TO MINERAL EXPLORATION
Khalid S. Essa
Department of Geophysics, Cairo University, Giza, Egypt
[email protected]
An inversion algorithm is developed to estimate the depth and
associated model parameters of the anomalous body from the
gravity or self-potential (SP) whole measured data. The problem
of the depth (z) estimation from the observed data has been
transformed into a nonlinear equation of the form F(z) = 0. This
equation is then solved for z by minimising an objective
functional in the least-squares sense. Using the estimated depth
and applying the least-squares method, the polarization angle
and the dipole moment or the amplitude coefficient are
computed from the measured SP or gravity data, respectively.
The proposed approach is applicable for a class of geometrically
simple anomalous bodies such as the semi-infinite vertical
cylinder, the dike, the horizontal cylinder and the sphere, and it
ASEG-PESA 2010 Conference Handbook
PNG harbours great wealth in flora, fauna, mineral resources and
its people, but these have long remained hidden by junglecovered mountains, extensive lowland swamps and many outlying
volcanic and earthquake-prone islands. New Guinea came to the
attention of science in the 17th century with the discovery of the
bird of paradise, a great curiosity to Europeans. Expeditions into
PNG in the 19th century became fiercely competitive amongst
naturalists, expeditions which would lay the geological
groundwork for huge copper-gold, and oil and gas discoveries in
the 20th century (Rickwood 1990). Oil Search, incorporated in
PNG in 1929, has continued this spirit of discovery with
extensive geologic and scientific surveys through its 80 year
history, contributing to the PNG oil boom throughout the 1990’s
and to the upcoming LNG boom from 2014 into the 2030’s.
Geologic advances have been made in the dating of sequences,
understanding of the development of mountain belts in 2D and
(soon) 3D, and the prediction of fluid migration into traps.
Engineering innovations have been profound, in heli-drilling,
seismic acquisition and now in the construction of an LNG
stream. But what of the future? Science in PNG will continue to
move forward; the application of 3D seismic in the offshore will
open new frontiers, and the recent granting of coal-bed-methane
licences in the swampy lowlands will test our knowledge and our
science. There is no doubt that scientific endeavor will bring to
light yet more wealth in Papua New Guinea.
QUANTITATIVE SEISMIC INTERPRETATION FOR
CHARACTERIZING CARBONATE DIAGENESIS –
AN ELK/ANTELOPE GAS FIELD STUDY
Adrian Goldberg1*, Moyra Wilson2 and Sioni Sioni1
Australia, QLD, Australia
2The Institute for Geoscience Research, Department of Applied
Geology, Curtin University, Perth, WA, Australia
1InterOil
[email protected]
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ABSTRACTS
[email protected]
Abstracts
The Elk/Antelope gas field is hosted in the Miocene reefal and
deepwater carbonates in Papua New Guinea. The carbonates
exhibit multiple diagenetic overprints and complex internal
seismic reflector heterogeneity.
The objective of this study is to identify the main cause(s) of
seismic reflectors within the Elk/Antelope gas field and to
ascertain if diagenetic boundaries are resolvable.
Wireline logs in the Elk-4, Antelope-1 and Antelope-2 wells
were corrected and P-Impedance logs were generated. Best fit
wavelets for ties to zero offset VSP’s and 2D seismic lines were
made at each well. Wireline logs were correlated with thin
section petrological studies to characterize the lithological facies
and diagenetic overprint.
We conclude that chronostratigraphic boundaries are associated
the highest amplitude seismic reflection events within the gas
field and a base dolomite diagenetic boundary is only clearly
evident in VSP data.
ABSTRACTS
THE GEOPHYSICAL RESPONSE OF THE TUPINDA
CU-AU-MO PORPHYRY PROSPECT, TABAR ISLANDS,
PAPUA NEW GUINEA
Brendan Howe1* and Adam Kroll2
1Barrick Gold, Perth, WA, Australia
2UTS Geophysics, Perth, WA, Australia
[email protected]
The Tupinda porphyry prospect is located in the Tabar Islands
Group of Papua New Guinea, approximately 80 km NW of the
supergiant Lihir epithermal gold deposit (45 Moz Au).
Geophysical data over the prospect include airborne magnetics
and radiometrics, ground pole-dipole induced polarization and
resistivity, gradient array induced polarization, petrophysics,
and airborne time domain electromagnetics.
All geophysical datasets clearly identify the footprint of the
porphyry body and associated alteration system. The magnetics
show a central high representing the magnetite altered potassic
core surrounded by a circular zone of low response indicative
of magnetite destructive phyllic alteration. The radiometrics
show a discrete potassium anomaly overlapping the magnetic
anomaly. The pole-dipole IP data display a resistive chargeable
zone coincident with the magnetic anomaly. Mid to late
time airborne EM data exhibit a broad sub-circular resistor
coincident with the mapped limits of the alteration system.
Field mapping and drilling of the prospect are consistent with
the geophysical data. Outcropping potassic alteration is observed
at the location of the magnetic and radiometric anomalies. Drill
core shows widespread disseminated sulphide mineralization
consistent with the chargeable response observed in the IP data.
Predominantly fresh felsic lithologies intersected in the drilling
concur with the resistor measured in the airborne EM data.
A more complex relationship exists between grade and magnetic
susceptibility, with some areas displaying a good correlation and
other demonstrating a more cryptic relationship which may be a
function later overprinting geological events.
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LOGISTICS OF DATA ACQUISITION IN TROPICAL,
RUGGED TERRAIN – THE AIRBORNE GEOPHYSICAL
SURVEYS OF THE PNG HIGHLANDS AND PAPUAN
PENINSULA
Gregory J. Street1*, M. Reeve-Fowkes2 and D. Cowey2
Geoscience, Perth, WA, Australia
2Fugro Airborne Surveys, WA, Australia
1International
[email protected]
Between 2005 and 2008 two areas of the PNG highlands and the
Papuan Peninsula were surveyed in the world’s largest helicopter
magnetic and radiometric survey. Three major factors affected in
the planning of this survey; the extreme terrain, the remoteness
and the climatic conditions. This survey ranged in altitude from
sea level to the top of Mt Wilhelm (approx 14 500 ft or 4509 m)
and thus a high performance helicopters were needed.
Prevailing weather conditions resulted in need to split the survey
lines into smaller segmented sections and fly areas on an
opportunistic basis when conditions were suitable. Area 1
consisting of some 1262 survey lines was flown in 10 500
separate line segments. Software was developed for monitoring
and processing of individual line segments. The extreme nature
of the country and the variable, rapidly changing, weather and
remoteness of the survey operations required dedicated Search
and Rescue (SAR) planning and aircraft monitoring.
Survey bases were located as close as possible to the area being
flown. This enabled the local weather to be closely monitored
and also made the daily test-lines more representative of the
local survey area. As the survey drew to a close the last
remaining sections were in the most difficult areas. The final
200 km took almost one month and the last 5 km a week to
complete. Despite all difficulties of working in this mountainous
region the detailed planning resulted in the survey being
completed in less than the projected timeframe.
Day 2 Session 4 Stream 3
ENGINEERING APPLICATIONS FOR GEOPHYSICS
RESISTIVITY IMAGING USING FLEXIBLE ELECTRODE
COMBINATION FOR MULTI-HOLE-SURFACE
RESISTIVITY SURVEYS
Jingping Zhe
ZZ Resistivity Imaging Pty Ltd, Adelaide, SA, Australia
[email protected]
This paper describes the use of flexible electrode combination in
multi-borehole-surface resistivity surveys. Traditionally resistivity
imaging adopts standard electrode arrays, such as Schlumberger,
Wenner or dipole-dipole. These arrays were originally designed
for use in surface surveys. For cross-hole or borehole-surface
resistivity surveys, no analogous standard array design exists.
We introduce a new method to complete a multi-boreholesurface resistivity survey, which has significant application in
civil engineering and environmental exploration. In the method,
electrodes may be positioned in both surface and boreholes
positions with almost no limitation on the amount of electrodes
able to be used in the boreholes. Real cases are presented
showing that the multi-borehole-surface resistivity method is
capable of solving some very difficult civil engineering
exploration problems. This method is based on advanced
ASEG-PESA 2010 Conference Handbook
Abstracts
ANATOMY OF THE ‘LUSI’ MUD ERUPTION, EAST JAVA
Mark Tingay
Curtin University, Bentley, WA, Australia
[email protected]
Early in the morning of the 29th of May 2006, hot mud started
erupting from the ground in the densely populated Porong District
of Sidoarjo, East Java. With initial flow rates of
~5000 cubic meters per day, the mud quickly inundated
neighbouring villages. Over two years later and the ‘Lusi’
eruption has increased in strength, expelling over 140 million
cubic meters of mud at an average rate of approximately
90 000 cubic meters per day. The mud flow has now covered over
700 hectares of land to depths of over 25 m, engulfing a dozen
villages and displacing approximately 40 000 people. In addition
to the inundated areas, other areas are also at risk from subsidence
and distant eruptions of gas. However, efforts to stem the mud
flow or monitor its evolution are hampered by our overall lack
of knowledge and consensus on the subsurface anatomy of the
Lusi mud volcanic system. In particular, the largest and most
significant uncertainties are the source of the erupted water (shales
versus deep carbonates), the fluid flow pathways (purely fractures
versus mixed fracture and wellbore) and disputes over the
subsurface geology (nature of deep carbonates, lithology of rocks
between shale and carbonates). This study will present and
overview of the anatomy of the Lusi mud volcanic system with
particular emphasis on these critical uncertainties and their
influence on the likely evolution of disaster.
THE APPLICATION OF SEISMIC TECHNIQUES IN THE
DEVELOPMENT OF THE MILLENNIUM URANIUM
DEPOSIT, NORTHERN SASKATCHEWAN, CANADA
Garnet Wood*, C. O’Dowd and P. Dueck
Cameco Corporation, Saskatoon, Saskatchewan, Canada
(vertical seismic profiling), and two Side-scan (single hole)
borehole seismic surveys. This was the first time a seismic
program of this magnitude was undertaken in advance of mine
development in the Athabasca Basin. All surveys successfully
mapped the unconformity and post-Athabasca structure at
various scales.
PROCESSING OF BOREHOLE RADAR DATA FOR 3D
LOCATION OF STRUCTURES AND UNDERGROUND
TUNNELS FOR SHAFT RISK MITIGATION, CASE
EXAMPLES FROM THE BUSHVELD OF SOUTH AFRICA
Carina Kemp1*, Kzek Trofimczyk2 and Petro Du Pisani2
1GeoMole Pty Ltd, Eveleigh NSW, Australia
2Anglo Technical
[email protected]
Borehole radar is a powerful high resolution structural mapping
tool. However current technology is limited to a non-directional
antenna in the 10–100 MHz frequency band. This directionality
can be overcome using multiple surveys from multiple boreholes
that image the same structure or by exploiting prior knowledge
of the formations under investigation, e.g. formation dip.
This paper presents two case examples. In the first, radar
surveys were acquired in three shaft boreholes drilled to
investigate a shaft design at Amandelbult Platinum Mine. In the
second, borehole radar is used to map the location of old mine
workings at Rustenburg Platinum Mine for a new ventilation
shaft development. In both cases, borehole radar detected and
mapped steep structures that could impact on the shaft design
and support requirements. Borehole radar results from all
boreholes were processed and migrated into 2D planes around
the borehole. The results were then interpreted using primitive
modelling. 3D interpretations were synthesized using raytracing and compared to the actual results. Multiple simulations
of these types were conducted to narrow down the possibility of
the true location of the structure in 3D space. This paper then
explores the best drill-hole design for borehole radar to enable
the location of various types of structures in 3D space.
[email protected]
The Millennium uranium deposit is located within the Athabasca
Basin of northern Saskatchewan, Canada, hosted within steeply
dipping Paleoproterozoic supracrustal rocks, overlain by greater
than 500 m of porous Manitou Falls Formation of the Athabasca
Group. An unconformity, which is also a major fluid conduit,
separates the basement lithologies from the overlying sandstone
units. Rock quality surrounding the deposit is compromised
because of the effects of the significant hydrothermal alteration
associated with the mineralization process. Post-Athabasca
structures, together with the unconformity, provide direct
conduits for the migration of large amounts of basinal fluids to
the general deposit area. To mitigate the risk involved with
mining in such a complex hydrogeological environment, several
projects were proposed as part of a pre-feasibility study for
potential mine development. Of these, seismic methods were
identified as the best tool to potentially map the location of the
unconformity, identify structurally complex zones and identify
alteration at both the mine and property scales. Subsequently,
comprehensive surface and borehole seismic programs were
completed in an attempt to increase confidence in shaft sinking,
delineate engineering hazards related to mine development, and
to provide information on the structural setting of the deposit.
The program consisted of a surface 3D survey, a stepout VSP
ASEG-PESA 2010 Conference Handbook
Day 2 Session 4 Stream 4
URANIUM EXPLORATION
APPLICATION OF 3D SEISMICS IN THE DELINEATION
OF U BEARING STRUCTURES AT RANGER 3 DEEPS
Angus McCoy1* and Milovan Urosevic2
Resources of Australia Ltd, WA, Australia
2Department of Exploration Geophysics, Curtin University, WA,
Australia
1Energy
[email protected]
Energy Resources of Australia Ltd (ERA) own and operate
the world class Ranger Uranium Mine located in the Northern
Territory. Recently, ERA has been undertaking extensive
exploration in the area which resulted in the discovery of
the very significant Ranger 3 Deeps (R3D) uranium resource,
down-dip but separate from the existing Ranger #3 orebody.
Extensive evaluation drilling work together with detailed pit
mapping and reinterpretation of historical data highlighted the
AUGUST 2010
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ABSTRACTS
resistivity inversion techniques, flexible electrode combination
along with a fast multi-channel data acquisition system. It can
easily be used for 3D resistivity multi-borehole-surface surveys.
Abstracts
importance of complex structural controls to the formation
of the Ranger orebodies.
Indistinct physical property contrasts and the depth and detail of
investigation required rendered traditional hard-rock geophysical
methods ineffective at defining key contact and fault locations.
Seismics was considered the only technique potentially capable
of delivering the information at the required resolution.
Feasibility investigations including velocity and density
measurements, synthetic modelling simulations and trial VSP
and 2D traverses all showed that the technique had a high
probability of success. In 2008, a 3D survey over the R3D
area was also acquired and processed by the CHDG group
from Curtin University.
ABSTRACTS
The seismic data has dramatically improved confidence in the
placement of contacts and steep fault controls to mineralisation.
Acoustic impedance inversion processing, attempted for the first
time in a hard-rock environment, is showing promise as an aid
to geological modelling, exploration targeting and potentially
advanced geotechnical investigations.
Exploration elsewhere in the lease is now benefitting from
another 3D survey with the expectation that similar
mineralisation bearing structures may also be identified from
this survey.
AIRBORNE ELECTROMAGNETIC SIGNATURE
OF A PALEOCHANNEL URANIUM DEPOSIT
Sean Walker1* and Adam Kroll2
1Aeroquest Surveys, Ontario, Canada
2UTS Aeroquest, Ontario, Canada
[email protected]
Reptile Uranium, a wholly owned subsidiary of Deep Yellow
Ltd, has been actively exploring four exclusive prospecting
licenses (EPLs) in Namibia since 2007. Prior exploration of
this area in the 1970’s and 80’s resulted in the discovery of
extensive Tertiary uranium mineralization hosted by paleochannels. Detailed airborne magnetic and radiometric data
acquired in 2007 shows good correlation with known surficial
mineralization, but provides no depth information about the
known channels, and does not identify potential buried
channels. In 2008, Aeroquest Surveys completed an AeroTEM
helicopter time domain electromagnetic (HTEM) survey over
the four EPLs. The EM data proved to be an excellent tool
for mapping the conductive material associated with both
near-surface and buried paleo-channels. There is generally
good correlation between the stronger AeroTEM responses and
the known mineralization. The HTEM data are inverted using
a 1-D layered earth algorithm to model the distribution
of conductivity laterally and with depth. The modeled data
effectively describe the lateral extent, thickness and relative
conductivity of the paleo-channels and have been found to be
very useful in directing the ongoing drill program both for the
delineation of known paleo-channels and for the drilling of
previously unknown paleo-channels. Successful trenching and
drill results from the Tubas-Oryx-Tumas paleo-channel system
clearly illustrate the important role that the HTEM survey
plays in the ongoing exploration on this project.
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UNCONFORMITY-RELATED URANIUM
IN SA – GEOPHYSICAL ANALYSIS
OF THE CARIEWERLOO BASIN
Tania Dhu*, Gary Reed, Tania Wilson, Wayne Cowley, Philip Heath,
George Gouthas and Martin Fairclough
PIRSA, Adelaide, SA, Australia
[email protected]
The Cariewerloo Basin, deposited on the eastern margin of the
Gawler Craton, South Australia, displays many similarities with
the Athabasca Basin of Saskatchewan, Canada, that are
considered key ingredients for unconformity-related uranium
mineralisation. These include gently folded Mesoproterozoic red
bed lithologies unconformably overlying faulted, reductanthosting Palaeoproterozoic crystalline basement intruded by
uraniferous A-type granites and comagmatic volcanics. The
basin contains mildly deformed red bed sediments of the
Pandurra Formation, that overly crystalline basement, including
high-grade metamorphic rocks, containing sheared graphitic
schists within the Hutchinson Group, Gawler Range Volcanics,
which is in turn intruded by Hiltaba Suite granites that are a
potential source of uranium.
An investigation of the region was undertaken using various
geophysical techniques. Basement depth estimates are created
using 3D modelling, drill-hole information and magnetic depth
estimates. Gradient strings are created for gravity data as
regional indicators of conduits for fluid flow. Textural analysis
of magnetic data is performed to map the presence and absence
of Gawler Range Volcanics. The information from these
different datasets is used to target a trial AEM survey that will
be flown over the region aimed at confirming depth to
basement and identifying conductive anomalies.
SPATIAL MODELLING OF MULTI-DISCIPLINARY
GEOSCIENTIFIC DATA FOR URANIUM EXPLORATION
OVER THE KUNJAR-DARJING BASIN, ORISSA – A GIS
APPROACH
V. Ramesh Babu*, A. K. Chaturvedi, A. Markandeyulu,
P. K. Srivastava and A. Chaki
Airborne Survey and Remote Sensing Group,
Atomic Minerals Directorate for Exploration and Research,
Department of Atomic Energy, Hyderabad, India
[email protected]
Application of Geographical Information System (GIS) for
identifying the spatial locations of target areas for uranium
exploration using multi-disciplinary geoscientific data is presented
in this paper. The data sets used in this study are Airborne
Gamma Ray Spectrometric (AGRS), Aeromagnetic (AM),
Satellite images, regional ground gravity and geochemical surveys
over one of the promising mobile Proterozoic Kunjar-Darjing
basins to the west of Singhbum Uranium Province (SUP), Orissa,
India. All these data sets are processed and interpreted
independently in terms of geology based on characteristics such as
intensity, frequency and texture of the images generated. Various
ratio maps generated from AGRS data were used as training
points for spatial modeling by building relationships (topology)
with the structures and geology interpreted from the magnetic and
gravity datasets. This study shows that integrating the geological,
geophysical, geochemical and other geodata in a GIS environment
provides valuable guidelines for geological mapping as well as
identifying target areas for uranium exploration.
ASEG-PESA 2010 Conference Handbook
Abstracts
8:30–10:30
Day 3 Session 1 Stream 1
GEOPHYSICS AND CARBON DIOXIDE ISSUES
RAPID GAS TRANSPORT IN THE NEAR-SURFACE
OF THE EARTH
Bruce L. Dickson
Dickson Research Pty Ltd, Gladesville, NSW, Australia
[email protected]
With governments around the world planning to spend vast sums
on disposal of CO2 to underground storage, it becomes very
important to understand the mechanisms of gas transport in the
earth. Conventional models of gas transport centres on diffusion
and advection. However, there has long been anecdotal and
experimental evidence for gas transport that is orders of
magnitude faster. The proposal a few years ago of microbubble
transport with vertical velocities of the order of 1 – 100 m/day,
dependant on microfracture size, provides answers to many of
the questions regarding these observations. Because the force
acting on the microbubble is buoyancy, flow will be vertical
with little dispersion. This presentation will review this theory
and some of the tests conducted to confirm such rapid vertical
velocities and consider means to indentifying zones of high gas
flow.
As well as possibly being problematic for CO2 storage, fast gas
transport also has some applications. Geochemists have long
used methods to detect traces of metals carried by gases from
deeply buried deposits to the surface. Selective leach methods
are then used to remove and analyze the weakly adsorbed traces.
Radon in soil gases is a classical method for locating uranium
but the results are often problematic with isolated areas in
regions showing higher radon responses than known deposits.
This resulted in much discussion on the mechanisms of rapid
gas movement. The ability of gas to flow from depth is
illustrated by the measurement of radon gas at the surface to
locate in-situ fires in coal seams in the Hunter Valley; fires
which are located at 300 – 450 m depth. Whether the radon is
from the source (burning coal) or picked up by the flowing gas
(CO2), the surface measurements of radon show anomalies
located vertically over the fires, confirming the vertical gas
movement.
4D SEISMIC MONITORING OF CO2 SEQUESTRATION
David Lumley
University of Western Australia, WA, Australia
[email protected]
WA is poised to embark on several major new energy
developments. These include $200+ Billion AUD investment in
new gas reserves that will begin production in the Carnarvon,
Browse and Bonaparte basins. Developing these new gas
reserves will require handling many Millions of tons per year
in CO2 released as a natural byproduct of the LNG process. To
avoid venting this natural CO2 into the atmosphere, which may
be bad for both the environment and business, the CO2 will have
ASEG-PESA 2010 Conference Handbook
to be disposed of safely. One of the best available options is to
accelerate nature’s course by re-injecting and storing it into deep
rock formations, termed “geo-sequestration”. Geophysical
monitoring of producing gas reservoirs will thus play an
important role in two ways:
(1) enhancing the gas recovery factor of these projects by
improving the reservoir model and understanding geologic
flow complexity, and
(2) monitoring any required CO2 injection to ensure it is being
safely stored in the subsurface for the long term.
In addition to petroleum applications, there is a strong interest in
developing clean-coal initiatives by capturing the CO2 generated
at coal-fired power plants and injecting it into the subsurface.
Geophysical techniques will therefore also play a key role in
monitoring and verification strategies for clean-coal CO2
sequestration projects. I will discuss our research at the UWA
Center for Petroleum Geoscience and how it relates to these
monitoring challenges for upcoming WA energy projects.
LAND VSP SEISMIC SOURCES EVALUATION: CO2CRC
OTWAY PROJECT CASE STUDY
ABSTRACTS
Day 3: Wednesday 25 August 2010
Roman Pevzner1*, Sergei Tcherkashnev2*, Anton Kepic1, Milovan
Urosevic1, Leon Dahlhaus2 and Shoichi Nakahishi2
1Curtin University of Technology, Perth, WA, Australia
2Schlumberger Oilfield Services, Perth, WA, Australia
[email protected]; [email protected]
It is widely accepted that, depending on acquisition technique,
vertical seismic profiling (VSP) can provide us with extremely
valuable information on seismic velocities (both P and S),
attenuation and anisotropy of seismic properties of the earth.
Subsurface images, obtained with offset or 3D VSP could
demonstrate superior resolution, signal-to-noise ratio and
repeatability of surveys in comparison to standard surface
seismic. These potential benefits are of great importance
for both reservoir characterisation and time-lapse seismic
monitoring. However in order to achieve them VSP surveys
should be acquired with proper survey design and optimal
source and receiver characteristics.
Modern 3C downhole VSP tools (such as VSI or similar array
seismic equipment) are able to record seismic signal in wide
frequency range (3–200 Hz) and provide high sensitivity and
vector fidelity. Thus the main hardware factor affecting quality
of VSP data is the seismic source. It can have different power,
stability of the wavelet, frequency content and variable pattern
of emitted wavefield including coherent noises.
In this paper we analyse land VSP data acquired with various
seismic sources in order to determine signal quality and its
repeatability. The data were acquired within the scientific
program of the CO2CRC Otway Pilot Project in 2007–2009
and includes zero offset and offset VSP in two neighbouring
wells (CRC-1 and Naylor-1, distance between boreholes is
~300 m) and 3D VSP data in CRC-1. A wide range of seismic
sources was used to acquire these vertical profiles; they include
weight drop sources, MV vibroseis (6000 lbs), IVI Mini-Buggy
vibroseis (16000 lbs) and a limited amount of explosive shots.
We evaluate each source from a seismic data quality perspective
(i.e. S/N ratio, image resolution, etc.) as well as acquisition
performance and environmental impact.
AUGUST 2010
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Abstracts
SEISMIC MONITORING OF CO2 GEOSEQUESTRATION:
CO2CRC OTWAY PROJECT CASE STUDY
Roman. Pevzner1*, M. Urosevic1, B. Gurevich1, V. Shulakova2,
A. Kepic1 and S. Sharma3
1CO CRC, Curtin University of Technology, Perth, WA, Australia
2
2CO CRC, CSIRO, Perth, WA, Australia
2
3CO CRC, Schlumberger Perth, WA, Australia
2
ABSTRACTS
[email protected]
The CO2CRC Otway Project is Australia’s first demonstration of
the deep geological storage of carbon dioxide. Its test site is
located in Victoria, onshore. Within the bound of the first phase
of the Otway project ~61 000 tonnes of CO2/CH4 mixture were
injected into depleted gas reservoir located at a depth of 2 km.
Second phase of the project is dedicated to injection of small
amount (up to 10 000 tonnes) of CO2-rich gas to saline aquifer
at depth of ~1.3 km. Time-lapse seismic is a powerful tool for
imaging of changes in the subsurface such as migration of CO2
within reservoir and assurance monitoring of possible leakage
to other formations. However imaging of gas-into-gas injection
(phase I) or injection of very small amounts (phase II) using
land seismic are complicated problems. To meet these challenges
a comprehensive seismic program is developed and being
implemented. It includes surface and borehole time-lapse seismic
surveys. First 3D survey was acquired in year 2000 to find
gas fields in the area, two more surveys were shot in 2008
(pre-injection baseline) and 2009 (first monitor, ~31 000 tonnes
of gas were injected to the date of survey), next survey is
scheduled at January, 2010. A number or repeated 2D surveys
were acquired over last several years to optimize 3D seismic
acquisition technique and investigate repeatability of land
seismic data.
In this presentation we discuss problems and preliminary results
of time lapse seismic monitoring of CO2 sequestration in Otway.
Day 3 Session 1 Stream 2
DEEPER PENETRATION AND GREATER CLARITY
INTERPRETATION OF HELIBORNE VTEM AND
MAGNETIC SURVEY DATA TO REFINE GEOLOGICAL
UNDERSTANDING OF BASE METAL EXPLORATION
IN THE CENTRAL AFRICAN COPPERBELT
Sarah Monoury1*, Bert De Waele1 and Chris Meyer2
1SRK Consulting, West Perth, WA, Australia
2Northcore Minerals Limited, Ndola, Zambia
[email protected]
This study presents the results of an interpretation of heliborne
electromagnetic (VTEM) and magnetic data over a base metal
tenement in the Central African Copperbelt in Zambia. The
study area is located in the “Domes Region” of the Copperbelt,
where shallow basement domes are overlain by the Katanga
Supergroup. The lower group of the Katanga Supergroup, the
Roan Group, contains a 20-m thick organic shale unit, known
as the Ore Shale, which hosts about 70% of Cu-Co
mineralisation in the Zambian Copper Belt. The outcrops
in the tenement are very limited due extended cover. The data
available were regional-scale geological maps associated with
some geochemical data on soils as well as Landsat imagery.
The geophysical data acquired cover approximately an area of
50 × 50 km. The interpretation was based on several processed
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AUGUST 2010
VTEM and magnetic grids and depth sections. The data
indicates a variety of correlated patterns of response. The
various responses relate to different parts of the stratigraphic
succession. Numerous linear features, mainly in the magnetic
dataset, were interpreted to represent an imbricate thrust-stack
of Roan Group sediments. As a result, the Ore Shale unit may
be structurally repeated within the tenement. However, no high
electromagnetic responses in VTEM could unequivocally be
ascribed to the Ore Shale. In consequence, the identification and
ranking of targets was based on the recognition of suitable
geological conditions for base metals mineralisation, rather than
direct electromagnetic or magnetic response.
THE DRYBONES KIMBERLITE: A CASE STUDY
COMPARISON OF ZTEM TIPPER AFMAG AND VTEM
AIRBORNE EM RESULTS
Vlad Kaminski, Jean Legault* and Harish Kumar
Geotech Ltd, Aurora, ON, Canada
[email protected]
Two airborne EM surveys were conducted over the DryBones
kimberlite by Geotech Ltd. The DryBones kimberlite is situated
roughly 45 km SE from town of Yellowknife, NWT. Initially
discovered in 1994, the kimberlite is located in DryBones
Bay and lies totally underwater, which averages at 38 metres
in depth. The kimberlite itself is further overlain by 65–75 m
of sediments, predominantly clay, till and sand. With
dimension 900 m by 400 m, it is one of the largest kimberlites
ever detected in Canada, yet has not undergone mining
development for diamonds making it an interesting airborne
geophysics test case.
A VTEM (heliborne time domain EM) survey flown in 2005
is compared to a ZTEM (heliborne tipper AFMAG EM) survey
flown in 2009. Both surveys appear to detect anomalous
responses over the pipe, however according to conductivitydepth transforms and skin-depth estimates, it is unlikely that
VTEM response is representative of the actual kimberlite,
buried more than 100 m underneath the conductive sediments.
It appears that the consolidated kimberlite might be too resistive
to be differentiated from host rock using conventional TEM
methods. On the other hand the ZTEM response appears
to be able to differentiate between the diatreme (consolidated
kimberlite) and the host rock, lying below the conductive
blanket. Forward modeling, inversion and imaging methods are
used to quantify the respective VTEM and ZTEM behaviour.
DEEP CONDUCTOR DELINEATION THROUGH
IMPROVED EMFLOW DATA PROCESSING
James Macnae1*, Russell Mortimer2 and Karen Gilgallon2
University, Melbourne, VIC, Australia
2Southern Geoscience Consultants, Belmont, WA, Australia
1RMIT
[email protected]
The EMFlow program is an industry standard for the rapid
transformation of AEM data to a conductivity-depth section.
Written in the 1990’s, it provides a means to deconvolve data
from any definable AEM system to the time-constant domain,
and thereafter to predict conductivity-depth structures. The
deconvolution to time-constant domain requires constraints for
optimum performance: these constraints are user-controlled and
can include causality, power-law or exponential extrapolation
and geometrical amplitude constraints.
ASEG-PESA 2010 Conference Handbook
Abstracts
THE IMPACT OF AEM RECEIVER NOISE LEVELS
ON DETECTION, DISCRIMINATION AND
RESOLVABILITY OF MARGINAL TARGETS
Magdel Combrinck
Geotech Airborne Ltd, Midrand, South Africa
[email protected]
Data with better signal to noise ratios will lead to detection
of new targets and better resolvability of existing ones.
Whereas published AEM (Airborne Electromagnetic) system
specifications contain enough information to calculate theoretical
target responses (signal), there are almost no references to noise
levels. This is understandable, as noise levels are very often
survey dependent and not only a function of the EM system,
but it also means targets with marginal responses cannot
be modelled with confidence.
The VTEM (Versatile Time Domain Electromagnetic)
helicopter-borne system was introduced by Geotech in 2002
and used for commercial surveys since 2003. Over the last
seven years, many changes were made to the system. One of
the most significant improvements is the reduction in receiver
noise levels. Although comparative data examples have been
presented to illustrate this point, little quantitative work has
been done on the implications this has for mineral exploration.
The objective of this paper is to illustrate the importance of
receiver noise levels on AEM surveys. Data from 25 VTEM
surveys performed in Australia from 2006 to 2009 were
analysed to determine an estimate for average noise reduction
during this time under real field conditions. Improvements in
detection, discrimination and resolvability of marginal targets are
discussed based on these numbers.
ASEG-PESA 2010 Conference Handbook
Day 3 Session 1 Stream 3
FORMATION GEOPHYSICS
THE VIRTUAL ROCK PHYSICS LAB
Eric Saenger
ETH Zurich, Zurich, Switzerland
[email protected]
We describe a virtual rock-physics laboratory where the focus
is on numerical wave propagation simulations of heterogeneous
materials on different scales. Forward as well as inversion
algorithms are developed and applied interdisciplinary. The
increasingly powerful computational resources, engineered in the
last twenty-five years, enable today very accurate and realistic
studies.
We focus on three different areas in science and observe
synergetic effects. Passive seismic low-frequency spectroscopy,
an emerging onshore hydrocarbon exploration technology. It will
be further developed with the focus on wave propagation issues.
Forward modeling studies will provide the basis to study
possible site effects and to transfer this method to offshore
applications. Non-destructive testing approaches of concrete and
other materials are based on methods well known in geophysics.
Wave propagation applications can be transferred and used.
Effective elastic properties, forward modeling studies as well as
imaging algorithms are applied in collaboration with partners.
A time reverse localization technique is developed to monitor
fracture growth. The rock physics of gas hydrate-bearing
sediments has been a lively discussed research topic. With the help
of well controlled computer experiments we want to resolve
some questions on first principles at the micro-scale. For this
purpose we use microtomographic images as direct input. This
approach is unique. The interconnecting element of all
approaches is the understanding and the application of elastic
wave propagation in complex structures.
ESTIMATION OF CARBONATE ELASTIC PROPERTIES
FROM NANOINDENTATION EXPERIMENTS TO REDUCE
UNCERTAINTIES IN RESERVOIR MODELLING
Osni de Paula12*, Marina Pervukhina3, Boris Gurevich23,
Maxim Lebedev2, Mariusz Martyniuk4 and Claudio Delle Piane3
1Petrobras
2Curtin University of Technology, Bentley, WA, Australia
3CSIRO Petroleum, WA, Australia
4University of Western Australia, Perth, WA, Australia
[email protected]
Petrophysical properties of carbonate reservoirs, which are the
majority of all hydrocarbon reservoirs worldwide, are much less
predictable than the properties of silisiclastic reservoirs. This
is mainly due to chemical interactions of carbonate rocks
with percolating fluids that cause dissolution, ion exchange,
and recrystallization in geological time. These processes result
in dramatic changes in density, porosity, and permeability
leading to inhomogeneity of carbonate rocks on micro- and
meso- scales. Quantification of the elastic variability of
carbonate grains on the microscale is the first step to constrain
models and to obtain more realistic predictions of practically
important rock properties of carbonate reservoirs. In this study,
we present elastic moduli of an oolite sample from the Dampier
Formation - Pleistocene of Southern Carnarvon Basin, Western
AUGUST 2010
PREVIEW
81
ABSTRACTS
Geotem Deep and VTEM data collected over the Table Hill
prospect in WA showed very small amplitude responses,
which when processed with commercial EMFlow indicated
an extensive conductor at depth. Initial drilling encountered
manganese mineralisation consistent with this deep conductor.
However, step-out drilling did not encounter similar
mineralisation even though the holes were sited to intersect the
imaged good conductor. The data were therefore reprocessed
with an improved deconvolution method in an RMIT version of
EMFLow. The specific improvement trialled was a novel matrix
conditioning method that provided significantly more stable CDI
results than simple matrix normalisation used in the commercial
EMFLow program. The resulting CDI sections showed
considerable detail within the deep conductive layer, where
the most conductive region was consistent with the discovery
hole, and less conductive regions were coincident with the lack
of mineralisation in the step-out drilling. Improvements in
data processing therefore were shown to provide very useful if
not essential geological detail at depth.
Abstracts
Australia, obtained by nanoindentation. Young’s moduli of this
highly heterogeneous sample are measured at 49 points regularly
distributed in a 70 × 70 mm rectangular grid on the sample’s
surface. The frequency diagram shows bimodal distribution
of the Young’s moduli oriented around values of 56 GPa and
144 GPa that correspond to low and high density components of
the grain respectively. These two solid phases are apparent in
the high resolution scanning electron microscope images. We
used the obtained moduli of this composite grain for numerical
modelling using finite element approach of elastic properties of
the carbonate sample from micro-Computed Tomography
images. The results compare favourably with the elastic moduli
obtained from acoustic velocities measured by ultrasonic
technique.
PROSPECT IDENTIFICATION USING AVO INVERSION
AND LITHOLOGY PREDICTION
Brad Bailey*, Robert Nesbit and Frazer Barclay
Schlumberger, Perth, WA, Australia
These results have been used to gain a better understanding of
injector pathways, pressure and water front movement, depletion
gas and baffles. The 4D has also been used to optimize well
positioning and well design.
The two monitor surveys were processed in parallel with a
dedicated 4D baseline survey to generate good quality full and
partial stack data. Production data together with 4D seismic
attributes has been used to update the initial rock physics model
that relates rock properties to production effects. It was found
that the initial rock model under-predicted the response to
reservoir pressure changes in the field. The updated rock
physics model has been used in an extensive modeling exercise
to determine the best attribute to detect and quantify increases
in reservoir pressures and saturation changes. Results show that
4D AVO attributes are crucial in discriminating areas of
increased reservoir pressure from free and depletion gas effects.
The most quantitative method is utilizing elastic inversion
attributes, followed by AVO intercept and gradient attributes,
with the least quantitative being amplitude difference from
partial stacks.
ABSTRACTS
[email protected]
Identifying prospects within a large study area is traditionally
a time consuming process. Schlumberger Reservoir Seismic
Services have produced an efficient prospect screening tool
in the form of a well log calibrated gas sand probability cube
derived from AVO inversion attributes. Pre-stack simultaneous
AVO inversion was performed on a 5000 sq/km multi-client
seismic survey to compute seismic elastic attributes (acoustic
impedance, Poisson’s ratio and density) which can be used
to generate lithology and fluid properties. The survey was
acquired in 2008 and is located offshore between the giant
Io/Jansz and Scarborough gas fields on Australia’s NW shelf,
with potential gas reservoir’s situated at multiple levels within
complex geology. Well log data from within the survey area
were calibrated to the seismic, from which wavelets were
estimated for each angle stack using the angle-dependant
reflectivity logs. Low frequency models were derived using log
data from wells both inside and outside the survey extents, in
conjunction with seismic velocities and guided by interpreted
horizons. Elastic attribute logs were generated from the wells
and used to produce non-Gaussian lithology probability density
functions (PDF), which in turn are utilised to generate a 3D gas
sand probability volume from acoustic impedance and Poisson’s
ratio volumes. The gas sand probability volume can be loaded
into Petrel where techniques such as volume rendering and
opacity are applied to quickly and efficiently screen for
potential prospects from which gas sand geobodies can be
extracted for volumetric analysis and further reservoir
characterisation.
QUANTITATIVE 4D INTERPRETATION – RELATING
THE SEISMIC TO PRODUCTION CHANGES AT ENFIELD,
NORTH WEST SHELF, AUSTRALIA
Megan Smith*, André Gerhardt and Peter Thomas
Woodside Energy Ltd, Perth, WA, Australia
[email protected]
4D seismic monitoring at the Enfield oil field has proved to be
a key tool for integrated reservoir management and unraveling
production insights since early in the field’s history. Enfield
began oil production in July 2006. Two monitor surveys have
been acquired over the field at 7 months and 2.5 year time steps.
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AUGUST 2010
Day 3 Session 1 Stream 4
MARINE ACQUISITION
BREAKING NEW GROUND – AGAIN! THE PEGASUS
SUB-BASIN OF THE EAST COAST BASIN, NORTH
ISLAND, NEW ZEALAND
Chris Uruski
GNS Science, Lower Hutt, New Zealand
[email protected]
The Pegasus sub-basin is underlain by thick Neogene
sediments, originally eroded from the Southern Alps, carried
across the Canterbury Plains by large rivers and by longshore
drift across the Chatham Rise offshore. Most of these
sediments were deposited across a margin transitional from
collisional along North Island to strike-slip through South
Island. Some of the sediment is carried along a channel
system that follows the subduction trench as far north as
Gisborne. Here it turns sharp right across the Hikurangi
Plateau. Beyond the Plateau, the channel follows the base
of the Plateau before disgorging into the Kermadec Trench,
a distance of 2000 km.
A large extensive gravity low underlies the sedimentary basin,
across which we have one 2D seismic line of reasonable quality.
This line shows a series of Neogene turbidites overlying possible
Cretaceous and Paleogene source rocks. Several large anticlines
overlie a blind thrust which apparently splays from the Bennioff
zone.
In the Pegasus sub-basin, the Bergen Explorer recently
acquired 3000 km of 2D seismic data for the Crown
Minerals unit of New Zealand’s Ministry of Economic
Development. This talk describes the data which confirms
the presence of a major sedimentary accumulation. The new
data will be provided free to a good home in support
of a future licencing round.
ASEG-PESA 2010 Conference Handbook
Abstracts
Maz Farouki1*, Simon Barnes2, Roald van Borselen2, Rob Hegge2
and Peter Aaron2
1Petroleum Geo-Services Exploration (Malaysia) Sdn. Bhd.,
Kuala Lumpur, Malaysia
2Petroleum Geo-Services, Weybridge, United Kingdom
[email protected]
In recent years, a full 3-D extension of Surface-Related Multiple
Elimination (SRME) has become available to address complex
multiples. True-azimuth 3-D SRME (TA 3-D SRME) aims
to predict the full 3-D nature of all surface-related multiples,
while making no assumptions about the subsurface geology.
The application of TA 3-D SRME on data acquired using multiazimuth towed streamer configurations has led to significant
improvements in multiple removal compared to the application
on data acquired in conventional narrow-azimuth towed streamer
mode. Multi-azimuth data from the Nile Delta is used to
compare results between narrow-azimuth 3-D SRME
and true-azimuth 3-D SRME. Multiples are among the toughest
challenges in processing seismic data in the Nile Delta, which
is characterized by a structurally complex dipping water bottom,
shallow gas charged channel systems in a compaction driven
overburden, overlying a complex anhydrite rich layer of
Messinian age. This overburden generates complex diffracted
multiples, both in the shallow section (water bottom multiples)
and in the deeper section (Messinian peg-legs).
The results indicate that the multi-azimuth 3-D SRME leads
to better results than conventional narrow azimuth 3-D SRME.
The azimuthal diversity inherent in the multi-azimuth data
allows for better multiple prediction and data reconstruction
of missing data when TA 3-D SRME is applied, compared
to conventional narrow-azimuth 3-D SRME.
STUDIES TO ENHANCE SEISMIC DATA PROCESSING
FOR FRACTURED BASEMENT IN THE CUU LONG
BASIN OF VIETNAM
Mai Thanh Tan1*, Mai Thanh Ha2, Phan Tien Vien3
1Hanoi University of Mining & Geology, Vietnam
2University of Oklahoma, USA
3PetroVietnam, Vietnam
[email protected]
The fractured granite basement is the primary petroleum
reservoirs in the Cuu Long basin, Vietnam. Due to the
basement’s complex geological structure, the seismic data quality
is very weak, and it is important to improve seismic data
processing quality, especially on improving the signal to noise
ratio. A series of studies has been conducted by the authors, in
order to help solving this problem.
From seismic models, we could clarify the influence
of complicated geological conditions, especially fractured
granite basement on the seismic data processing. The signals
received from deep structures and fractures basements are weak
and obscured by strong noise. The presence of volcanic,
high impedance contrast interfaces, complicated faulting system
in lower Miocene and Oligocene create strong noise and
multiples background, which might obscure seismic signal
received from deep layers.
ASEG-PESA 2010 Conference Handbook
Our studies in the fractured granite basement of Cuu Long Basin
show that, for large lateral variations in velocities of the area,
using the multi-arrival-solution migration algorithms, such as the
Controlled Beam Migration (CBM), improve the signal-to-noise
ratio, and help imaging steeply dipping events from fractured
basement. Faults and fractures play a key role in forming
effective porosity for hydrocarbon traps, mapping the location,
intensity, and orientation of these faults and fractures can help
delineate sweet spots and aid in the positioning of horizontal
wells.
In this paper, the authors present the complicated seismogeological characteristics of the fractured granite basement
of Cuu Long Basin, demonstrate the applications of CBM
to 3D seismic from the study area and how it improves the
imaging of the fractured basement reservoir. We co-render
multiple attributes in a single composite volume, to visually
cluster attributes that delineate different components of the
fracture system. For more convenient display of these
lineaments, we report a new method to automatically generate
volumetric rose diagrams on user-defined n-inline by
m-crossline analysis windows spanning the entire seismic
volume.
SEISMIC REPROCESSING AND AVO INVERSION
OF THE NORTHERN FIELDS 3D (GIPPSLAND BASIN)
ABSTRACTS
MULTI-AZIMUTH 3D SURFACE-RELATED MULTIPLE
ELIMINATION – APPLICATION TO OFFSHORE NILE
DELTA
Jan Rindschwentner1, Jarrod Dunne1* and Yoong-Ern Lee2
1Nexus Energy, Southbank, VIC, Australia
2CGG Veritas
[email protected]
Geo-steering of the Longtom-3 and Longtom-4 development
wells was based on an AvO inversion attribute that has,
to date, proven reliable in highlighting thick, gas-filled sands.
In-field and near-field opportunities exist for adding upside
to the Longtom field development, although attribute support
has been hampered by coherent noise and resolution limitations.
Reprocessing of the Northern Fields 3D within VIC/P54
was undertaken with the specific objectives of reducing
multiples and flattening gathers to improve upon and extend
the existing AvO inversion dataset.
The reprocessing also provided an opportunity to trial the new
Shallow Water Demultiple (SWD) technique in an ideal setting
to gauge its ability relative to common demultiple methods. The
application of SWD resulted in a stunning improvement to the
stack with 2D SRME, tau-p deconvolution and high-resolution
Radon demultiple delivering only modest further improvements.
Three iterations of horizon-consistent velocity analysis ensured
flat gathers, particularly near volcanic horizons whose strong
interval velocity contrasts were not consistently honoured
in the original processing. Anisotropic Kirchhoff prestack time
migration was parameterised with a smoothly varying eta
function and this resulted in some large fault plane movements,
which could increase our reserves estimation for the Longtom
field.
Revisiting the AvO inversion is expected to bring measurable
improvements stemming from the use of multiple substacks
as input, the extra well log data that is now available and
by incorporating seismic interval velocities into the low
frequency input model.
AUGUST 2010
PREVIEW
83
Abstracts
11:00–12:30
Day 3 Session 2 Stream 1
quantitative monitoring of variations associated with floodplain
ecosystems, and in particular processes connected with surface
water and groundwater interactions. This also has implications
for understanding the consequences of floodplain management.
BETTER DELINEATION OF GROUNDWATER RESOURCES
In a pilot study in the Riverland of South Australia, we report
on spatio-temporal variations observed in near surface
determined from multi-temporal monitoring of a floodplain
with AEM data. Significant increases and decreases in ground
conductivity have been observed in particular locations adjacent
to the river and on the floodplain, indicating areas where water
levels associated with the underlying saline groundwater system
have dropped, and others where it may have risen. These
variations are attributed in part, to floodplain management
strategies, including an operational salt interception scheme
(SIS) and to changes in the regulated height of the river. The
results also suggest that some parts of the river have changed
from gaining to losing sections, indicating that the SIS may be
achieving it’s desired objective, namely of extract saline
groundwater before it discharges into the Murray River.
USING AEM DATA AS PART OF AN INTEGRATED
ASSESSMENT OF THE SALINITY HAZARD AND RISK TO
GUNBOWER STATE FOREST AND THE RIVER MURRAY
FLOODPLAIN IN THE GUNBOWER ISLAND-BARR CREEK
REACH OF THE MURRAY RIVER, SE AUSTRALIA
Kok PianTan1*, K. C. Lawrie1, L. Halas1, H. Apps1, K. Cullen1, R. C. Brodie1,
L. Gow1 and V. Wong2
1Geoscience Australia, Canberra, ACT, Australia
2Southern Cross University, Lismore, NSW (formerly Geoscience
Australia)
[email protected]
ABSTRACTS
In 2007 the Australian Government funded an AEM survey
(acquired with the RESOLVE frequency domain system)
to provide information in relation to salinity management issues
in the River Murray Corridor, including the Gunbower Island
to Barr Creek sub-project area.
The study found that healthy vegetation along the Murray River
is generally associated with river ‘flush zones’, where fresh
groundwater is present to depths of up to 20 m in zones up to
1.5 km in width (e.g. in Gunbower Forest). Groundwater and
salinity gradients suggest salt mobilisation from irrigated lands is
adversely affecting vegetation health along the western boundary
of the Forest. Overall, in the southern half of the project area
the Murray River would appear to be a losing system, with
a low short to medium term risk of off-site movement of salt
into the River through the groundwater system.
In the northern half of the area there are discontinuous flush
zones, the groundwater levels are closer to surface, and the river
system may be a gaining system in places, with a moderately
high salinity risk. Also, the Loddon River, Murrabit River and
Barr Creek have no flush zones developed, and are potentially
gaining systems at increased salinity risk.
Overall, the AEM and remote sensing data analysed in this
study provide a new spatial context for assessing salinity hazard
and risk, although there is a need for further ground validation
and analysis including hydrodynamic modelling. The data might
be used to guide plans for future salt interception in this area.
‘THE TIMES THEY ARE A-CHANGIN’ – FACTORS
AFFECTING OBSERVED SPATIO-TEMPORAL PATTERNS
IN GROUND CONDUCTIVITY ALONG THE MURRAY
RIVER FLOODPLAINS, IN SOUTH EASTERN AUSTRALIA
Tim Munday1*, A. Fitzpatrick1, V. Berens2, A. Viezzoli3 and K. Cahill1
1CSIRO, Perth, WA, Australia
2Department of Water Land and Biodiversity Conservation,
Adelaide, SA, Australia
3Aarhus Geophysics ApS, Aarhus, Denmark
[email protected]
The recent advent of calibrated airborne EM systems, coupled
with effective ground-based calibration procedures and more
robust inversion tools that can account for system geometry,
have given added impetus to their deployment as tools to aid the
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AUGUST 2010
Overall, these results suggest that airborne EM systems
should now be considered as one means for quantifying spatial
changes in the amount of salt stored on the floodplain, for
monitoring the effects of particular management strategies,
and for understanding floodplain processes.
SEISMIC SIGNATURE OF HIGH PERMEABILITY
SANDSTONE; PERTH BASIN; WESTERN AUSTRALIA
Majed AlMalki*, Brett Harris and J. Christian Dupruis
Department of Exploration Geophysics, Curtin University, Perth,
WA, Australia
[email protected]
Significant improvements in the quality of seismic methods
and equipment in recent decades have facilitated new ways of
interpreting hydraulic parameters from seismic data. Although
a direct relationship between seismic wave propagation and
hydraulic permeability is illusive, indirect relationships may still
be of considerable practical value for interpreting various forms
of seismic data. Multi-frequency full wave form sonic logs have
been acquired in NG3, a cored borehole drilled into the shallow
Yarragadee Formation. The objective of the survey was to better
understand the relationship between velocity, frequency spectra,
amplitude and the formation hydraulic characteristics for shallow
high permeability sandstones. This dataset was collected
at four center frequencies; 1 KHz, 3 KHz, 5 KHz and 15 KHz
respectively. The full wave form (FWF) sonic logging tool
consisted of 4 receivers and 1 transmitter. All four frequencies
were acquired over an interval which spanned 55 to 87 m. FWF
sonic logs at 1 and 15 KHz were acquired over the full depth
of NG3 (~0 to 200 m). This data was acquired over such a
wide range of frequencies to achieve the best possible acoustic
characterization achievable using a monopole source in a
mudded drill hole (i.e. for compressional and Stoneley waves).
The results of this work clearly demonstrate velocity changes
with frequency for compressional waves which in turn relate to
differences in lithology. The largest differences in velocity were
observed when comparing highest frequency (e.g. 15 KHz) and
lowest frequency (e.g. 5 KHz) datasets in high permeability
zones. The frequency dependence of velocity is clearly
illustrated from these field data but the underlying principles
which lead to these differences are yet to be fully explained.
These exciting results which illustrate frequency dependent
ASEG-PESA 2010 Conference Handbook
Abstracts
Day 3 Session 2 Stream 2
DEEPER PENETRATION AND GREATER CLARITY
GEOLOGICAL INTERPRETATION OF THE 2008 SEISMIC
REFLECTION, REFRACTION AND MAGNETOTELLURIC
DATA FROM THE NORTHERN EYRE PENINSULA,
GAWLER CRATON
Russell J. Korsch1*, G. L. Fraser1, R. Dutch2, N. L. Neumann1, B. Bendall2,
A. Reid2, R. S. Blewett1, W. Cowley2, A. Nakamura1, T. Fomin1
and P. Milligan1
1Geoscience Australia, Canberra, ACT, Australia
2Primary Industries and Resources South Australia, Adelaide,
SA, Australia
[email protected]
A deep seismic reflection profile and coincident refraction and
magnetotelluric data were acquired across the northern Eyre
Peninsula, Gawler Craton in 2008 to enhance the prospectivity
of the Gawler Craton for uranium and geothermal energy, by
establishing the regional geodynamic framework and improving
our understanding of the crustal architecture. The seismic line
crossed the western boundary of a region of elevated surface
heat flow, termed the South Australian Heat Flow Anomaly
(SAHFA). This broad zone correlates with elevated surface
heat production values, associated with high heat producing
granites, and thus the elevated surface heat flow is attributed
to crustal enrichment in U, Th and K.
The seismic line crosses several tectonic domain boundaries
in the Gawler Craton, including between the Archaean core
of the craton and younger domains to the east and west. It also
crossed the Kalinjala Shear Zone, which is a key structure
in the southern and central Gawler Craton, defining a boundary
between Hutchison Group sedimentary rocks and Donington
Suite granites in the south. This shear zone dips moderately to
the east and appears to sole onto a detachment in the mid crust.
The seismic line also crossed the boundary between the Olympic
Fe-oxide Cu-Au-U Province (host of Olympic Dam and
Prominent Hill deposits) in the east, and the Central Gawler Au
Province in the west, and tested for different crustal architecture
between the two mineral provinces. The seismic line crossed
southern outcrops of the Pandurra Formation and remnants
of Corunna Conglomerate – these two basins lie above and
below the Gawler Range Volcanics, respectively, and each has
potential for hosting unconformity-related U mineralisation.
A final interpretation of the reflection, refraction and MT data
will be completed by December 2009 and the results included
in the extended abstract to be submitted in March 2010.
CAN A BOREHOLE CONDUCTIVITY LOG DISCREDIT
A WHOLE AIRBORNE EM SURVEY?
Yusen Ley-Cooper* and Aaron Davis
Geoscience Australia, Geospatial & Earth Monitoring Division,
Canberra, ACT, Australia
[email protected]
ASEG-PESA 2010 Conference Handbook
Airborne EM surveys are now a well-established method for
quickly investigating the ground in order to assess what lies
beneath the surface. The wide variety of existing AEM systems
with different specifications designed to detect different targets,
complex electronics and particular understanding required
to comprehend how data is processed (transformed or inverted)
from voltages to conductivity and depths has created the need
to “validate” the AEM results with more conventional methods
of “ground truth”. One such method is borehole conductivity
logging.
When comparing data sets of different origins, such as AEM
and down-hole conductivity logging, caution must be used.
Immediately evident is the considerations of scale: the bulk
conductivity from an airborne survey is affected by large-scale
structures such as discontinuous layers and regional faults;
whilst borehole skin depth and the conductivity values are
affected by casing materials, voids, temperature and calibration.
Conductivities measured from boreholes come from an invasive
method, where drilling can disrupt the in situ layering and
material conditions. This creates uncertainty in conductivity
measurements. Airborne data can also be incorrectly processed
and interpreted by using incorrect wave forms, frequencies,
and altitudes, or by not taking proper care when correcting
for instrument drifts.
Borehole conductivity logging can successfully reduce the
influence of calibration errors in AEM data but boreholes are
usually sparsely concentrated and subject to calibration errors
of their own. Therefore, the need for having confidence works
both ways.
RESTORING THE CONTINENT-OCEAN BOUNDARY:
CONSTRAINTS FROM LITHOSPHERIC STRETCHING
GRIDS AND TECTONIC RECONSTRUCTIONS
Joanne Whittaker1*, Nick Kuznir2, Simon Williams1, Dietmar Muller1
1School of Geosciences, The University of Sydney, NSW, Australia
2Department Earth and Ocean Sciences, University of Liverpool,
United Kingdom
[email protected]
We explore the tectonic formation of the passive Australian
Southern margin through a series of plate tectonic
reconstructions where we reconstruct the position of Australia,
relative to East Antarctica, all the way back to the onset
of continental rifting.
Recent tectonic models describing motion between Australia and
Antarctica fail to accurately restore relative motion that occurred
during continental rifting, prior to continental break-up and the
onset of seafloor spreading. In order to accurately reconstruct
the pre-rift or ‘full-fit’ position of Australia relative to
Antarctica it is necessary to restore the thinned continental
margins to their unstretched, pre-rift configuration. Once
restored, the pre-rift positions are used to compute ‘full-fit’
poles of rotation for Australia relative to Antarctica.
We use an inboard and an outboard interpretation of the
present-day Continent-Ocean Boundary (COB) to undo thinning
of the conjugate Australian-Antarctic passive continental
margins. We start with the present-day COB positions,
interpreted from a combination of geophysical and geological
data. We then integrate lithospheric thinning grids, derived
using satellite gravity inversion, along NW-SE striking tectonic
AUGUST 2010
PREVIEW
85
ABSTRACTS
attenuation and velocity for both Stoneley and compressional
waves appear to be related to the permeability at the test site.
New laboratory experiments are being designed to help provide
a more complete understanding of field experimental results.
Abstracts
flowlines that describe the oblique direction of motion that
affected this margin during continental rifting and early seafloor
spreading. We have also revised Euler poles describing the early
spreading history for the entire Australian-Antarctic system in
order to improve the reconstruction of relative motion between
Broken Ridge and Kerguelen Plateau.
Reconstructing this early tectonic history is important for
understanding the evolution of passive margin. It is especially
important for frontier basins such as the Sorell Basin, offshore
Tasmania, that form under transform conditions and can develop
surprisingly deep depocentres.
PORE PRESSURE PREDICTION IN HP/HT
ENVIRONMENT – NILE DELTA AREA
Day 3 Session 2 Stream 3
Patrizia Cibin1*, Mauro Della Martera1, Clara Andreoletti1
and Giulia Capponi2
1Eni E&P Division, Milan, Italy
2IEOC, Cairo, Egypt
FORMATION GEOPHYSICS
[email protected]
EXPERIMENTAL VERIFICATION OF THE PHYSICAL
NATURE OF VELOCITY STRESS RELATIONSHIP
FOR ISOTROPIC POROUS ROCKS
The necessity to satisfy the world need for oil and gas pushes
oil companies to drill in conditions that are getting harder and
harder in terms of Temperature and Pressure. The drillers have
to know the conditions as precisely as possible before drilling
a new borehole. Generally, in complex and deep areas the more
traditional relationships linking interval velocities from seismic
time processing with the effective stress (and consequently the
pore/over pressure), are no longer enough to make a correct
prediction of the pore pressure. For this reason several methods
have been developed to try to obtain more appropriate velocity
fields, and in this paper we compare some of them, mainly CVA
(Continuous Velocity Analysis) in the time domain and Grid
Tomography, in the depth domain. We intend also to show
pressure prediction results that instead of being obtained directly
from velocities, are derived from different seismic attributes.
In particular we present some pressure predictions obtained by
seismic inversion products such as Ip (Impedence of wave P)
and Vp/Vs Ratio.
Marina Pervukhina
CSIRO Petroleum, WA, Australia
ABSTRACTS
data attributes, waveform correlation coefficient or other seismic
attributes to build initial impedance model. The model built with
this method could vertically reflect the trend of seismic facies
changes and horizontally overcome the mismatching between
local geological phenomenon and seismic horizons. This initial
model could descript more detailed changes in the seismic
facies, and enhance inversion accuracy under the complex
geological conditions.
[email protected]
Knowledge of stress dependency of elastic properties of rocks
is important for a variety of geophysical applications ranging
from pore pressure prediction in sedimentary rocks to seismic
monitoring of hydrocarbon production. Theoretical interpretation
of exponential stress dependency of elastic properties of rocks
based on a dual porosity concept has been tested using
laboratory measurements on dry sandstones. For those sandstone
samples, the following postulates of the theoretical model are
shown to be consistent with the experimental data: (1) linear
dependency of elastic compressibility on soft porosity and
(2) exponential decay of soft porosity and elastic compressibility
with effective stress up to 60 MPa. Magnitude of the variation
of stiff porosity with stress is shown to be comparable with
compliant porosity. However, this variation has a negligible
effect on rock compressibility up to 60 MPa. Soft porosity
estimated from the fitting coefficients of elastic compressibilities
is on the same order of magnitude but slightly lower than
obtained from strain measurements. These results confirm
applicability of the stress sensitivity model and hence provide
justification for using this approach to model the effect of stress
on properties of not only for isotropic, but also anisotropic rocks.
AN INITIAL ACOUSTIC IMPEDANCE MODELING
METHOD BASED ON SEISMIC ATTRIBUTES
Zha Shugui
Jianghan Oil Field Geophysical Research Institute, China
[email protected]
Initial impedance models played a crucial role in acoustic
impedance inversion. The traditional modeling is horizontally
interpolated by using inverse distance power method for
multiple wells, and vertically controlled by seismic horizons.
This method was relatively simple, and could not reflect the
seismic facies changes in complex geological conditions with
relatively low inversion accuracy.
Based on seismic attributes, the method introduced here
calculated the weight coefficient with the amplitude of seismic
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AUGUST 2010
The paper shows some results from different prospects
in Egypt – Nile Delta area, where the Oligocene targets present
very difficult drilling conditions in terms of High Pressure and
High Temperature.
Day 3 Session 2 Stream 4
MARINE ACQUISITION
ANISOTROPY ESTIMATION USING VSP
AND SURFACE SEISMIC DATA
Konstantin Galybin*, Sergei Tcherkashnev and Leon Dahlhaus*
Schlumberger Australia Pty Ltd, Perth, WA, Australia
[email protected], [email protected]
Anisotropic pre-stack depth migration is becoming a common
imaging practice in oil and gas industry because of its enhanced
imaging capabilities. It is a slow, iterative process that greatly
depends on apriory knowledge of anisotropy in the imaged
subsurface. Here a quick and robust workflow of estimation
of anisotropy is presented. This workflow utilizes knowledge
of lateral velocity variations, which often mask themselves as
anisotropy, from the stacking velocities of the surface seismic
data and combines this with the VSP data. Acquisition of a
simple zero-offset Vertical Seismic Profile (VSP) provides
starting place for validation of stacking velocities, and hence
ASEG-PESA 2010 Conference Handbook
Abstracts
BROADBAND MARINE TOWED STREAMER
ACQUISITION; SOUTH CHINA SEA CASE STUDY
Tim Bunting
WesternGeco
[email protected]
The effect of the sea surface ghost on marine seismic acquisition
is well understood. Shallow tow geometries recover high
frequencies at the expense of attenuating low frequencies and
deep tow geometries recover low frequencies at the expense
of attenuating high frequencies. In recent years two dual
streamer tow depth solutions (Over-Under and Sparse-Under)
have been deployed, both of which use two streamers which
are towed at two different depths.
A 2D survey was acquired offshore China, in August 2009,
utilizing three separate streamer depths (5, 17 and 23 m). This
three streamer depth configuration allows for the benefits of the
two broadband solutions to be evaluated against each other and
against a shallow streamer single depth seismic measurement.
This paper will review the theory behind the two combination
techniques, compare the seismic datasets, and finalize with
some conclusions on the relative benefits both in terms
of seismic imaging and acquisition efficiency.
CONVERTED WAVE VELOCITY MODEL FOR HYDRATE
BEARING SEDIMENTS USING 4C OCEAN BOTTOM
SEISMOMETER DATA
Sanjeev Rajput
CSIRO, Perth, WA, Australia
[email protected]
Converted mode (P-S) exploration is complex in nature as it
requires sophisticated technologies. Different seismic experiments
composed of multichannel streamers, Ocean Bottom Seismometers
(OBS); Vertical Seismic Profiles (VSP) were carried out in 2002
at the Hydrate Ridge, offshore Oregon continental margin to map
the gas hydrate distribution, and to study the converted wave
properties within the hydrate stability zone. Gas Hydrates in sea
floor sediments can be identified though a geophysical indicator
known as Bottom Simulating Reflector (BSR). The BSR is a
strong seismic reflection that approximately mimics the sea floor,
cuts across reflections of stratigraphic origin, and has a negative
polarity, indicating that it results from a decrease in acoustic
impedance across an interface. Over the study area, the BSR
covers an area of approximately 44 km2.
In this study the data from two lines (20 Ocean Bottom
Seismometer along the ODP sites 1250 and 1251 and the 7
Ocean Bottom Seismometer along the ODP sites 1244 and 1245)
have been utilized to study the PS mode properties and to
investigate the sensitivity of the seismic velocities to the
ASEG-PESA 2010 Conference Handbook
presence of gas hydrate and associated free gas in the sediments.
The data have been processed for individual receiver gathers and
the seismic velocities have been estimated for all the 27 Ocean
Bottom Seismometers. As the accurate estimation of the
distribution and concentration of gas hydrates and free gas from
seismic velocities depends on the interval velocities of P- and
S-waves, the method is based on an interactive velocity analysis
of P and converted S waves in the tau-p domain applied to
the 4C Ocean Bottom Seismometer data. The results reveal a
complex velocity structure along specific sedimentary strata.
The results reveal that the converted wave velocity does not
show velocity anomaly in the hydrate-bearing sediments.
13:30–15:00
Day 3 Session 3 Stream 1
BETTER DELINEATION OF GROUNDWATER RESOURCES
USE OF THE SKYTEM AEM SYSTEM AS PART OF A
HYDROGEOLOGICAL SYSTEMS-BASED APPROACH TO
DELINEATION AND ASSESSMENT OF GROUNDWATER
RESOURCES IN THE DARLING RIVER FLOODPLAIN,
NSW, AUSTRALIA
Ross S. Brodie1*, K.C. Lawrie1, D.L. Gibson1, Y. Ley-Cooper1, A. Davis1,
J. Reid2, K.P. Tan1, L. Halas1, H. Apps1, J. Clarke1, T. Ransley1, J. Magee1,
K. Cullen1 and M. Richardson1
1Geoscience Australia, Canberra, ACT, Australia
2Groundprobe, Malaga, WA, Australia
[email protected]
Previous studies of groundwater systems and sustainable yields
in the Murray Basin identified significant unaccounted losses
of water from the Darling River system between Burke and the
Great Darling Anabranch. This has been attributed to the
combined effects of evaporation and leakage to the groundwater
system, although no significant groundwater resources have
previously been identified.
As part of the Broken Hill Managed Aquifer Recharge
(BHMAR) Project, established by the Australian Government to
secure Broken Hill’s water supply, the largest AEM survey in
Australia was commissioned to delineate potential groundwater
resources in the Darling Floodplain near Menindee. Two
SkyTEM AEM systems were used to acquire 31 834line km
of data over an area of 7541 sq km.
The use of iTEM-inversions enabled resistive anomalies in the
AEM data to be targeted within days of acquisition. Pore fluids
recovered from core obtained using sonic drilling technology
have confirmed the presence of significant quantities of fresh
to brackish groundwater in a number of large, relatively discrete
targets at depths ranging from 10 to 120 m. Prospective aquifers
occur in the Pliocene and younger aquifers.
Important to the assessment of the potential groundwater
resource, has been the use of the AEM data to map river leakage
zones and map groundwater flow paths. These data provide a
framework for detailed hydrogeochemical analysis to estimate
recharge rates and sustainable yields of the aquifers. Overall,
selection of the appropriate AEM technology capable of
mapping the key elements of the hydrogeological system has
been crucial to groundwater resource delineation and assessment.
AUGUST 2010
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ABSTRACTS
input into the isotropic 2D velocity model, as well as a well tie
that can be used in estimation of anisotropy from a CMP gather
at the well location. The CMP gather is thus corrected for
normal moveout using an isotropic 2D velocity model and then
artificially moved out using an isotropic 1D model derived from
VSP measurements. The resulting CMP gather can be used in
interactive 1D anisotropy estimation. The results of anisotropy
estimation can be used to populate a 3D model for anisotropic
pre-stack depth migration. This approach can also be extended
to evaluate azimuthal variations in anisotropy.
Abstracts
MAPPING SEA WATER INTRUSION (SWI) USING
THE TEMPEST AEM SYSTEM IN COASTAL PLAIN
AQUIFERS NEAR DARWIN, NORTHERN TERRITORY,
AUSTRALIA
Kenneth C. Lawrie1, J. Sumner2, Y. Ley-Cooper1, A. Davis1, M. Costelloe1,
S. J. Tickell2, P. English1, K. P. Tan1, L. Halas1, H. Apps1 and K. Cullen1
1Geoscience Australia, Canberra, ACT, Australia
2Water Resources Branch, NRETAS, NT, Australia
[email protected]
ABSTRACTS
This project reports on the use of AEM data to assess the
potential risk of SWI in the coastal aquifers of the Darwin area.
Regional AEM data (5 km line spacing) were collected as part
of Geoscience Australia’s Onshore Energy Security Program,
while infill data (555 m line spacing), funded by the National
Water Commission, was acquired in the Koolpinyah and
Marrakai priority areas.
Preliminary analysis of the AEM dataset indicates that the
TEMPEST system has mapped a complex SWI interface across
the north of the project area. Also, the survey appears to have
differentiated other key elements of the hydrostratigraphy
including Tertiary laterites, a Cretaceous aquifer system that
unconformably overlies the Proterozoic dolomites, and a karstic
interface at the top of the dolomite sequence. The AEM survey
has also mapped additional dolomite in karst environments that
hold potential for additional groundwater resources.
At Howard Springs, conductive anomalies within a major
structural lineament suggest preferential flow of saline
groundwater for >6 km inland to within a couple of kilometres
of producing bores. Similarly, conductive anomalies that occur
beneath the Adelaide River floodplain are consistent with
extensive leakage of saline groundwater into the underlying
dolomite aquifer, with structural control again indicated at depth.
Overall, this survey has highlighted the potential risk of SWI
to the karstic aquifers in the Darwin area. Also, the combination
of different flight line spacing depending on priority setting
is a cost-effective way to provide baseline hydrogeological data.
A drilling program is planned to validate the AEM data.
IDENTIFYING MANAGED AQUIFER RECHARGE (MAR)
ENGINEERING OPPORTUNITIES USING AIRBORNE
ELECTROMAGNETICS (AEM): THE BROKEN HILL
MANAGED AQUIFER RECHARGE (BHMAR) PROJECT,
NSW, AUSTRALIA
Kenneth Lawrie1, R.S. Brodie1, D.L. Gibson1, Y. Ley-Cooper1, A. Davis1,
J. Reid2, K.P. Tan1, L. Halas1, H. Apps1, J. Clarke1*, T. Ransley1, J. Magee1,
K. Cullen1 and M. Richardson1
1Geoscience Australia, Canberra, ACT, Australia
2Groundprobe, Malaga, WA, Australia
[email protected]
Prolonged drought and climate change in SE Australia have
led the Australian Government to seek innovative strategies
to secure water supplies and deliver environmental benefits to
threatened river systems. One such example is at Menindee
(NSW), where alternative water storage options are being
sought to replace the Menindee Lakes storage system, which
experiences substantive evapotranspirative losses when filled.
Previously, the high cost of investigations, low level of
knowledge of risk, and time taken to fill hydrogeological
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knowledge gaps has been a deterrent to development of MAR
options, especially to pioneering projects in new locations. To
provide the baseline data required (at 80% certainty levels),
to identify engineering opportunities within a short (12 month)
timeframe, an AEM survey was flown to identify potential
MAR targets and groundwater resources.
Two SkyTEM systems were used to acquire 31 834 line km of
data at 200 to 300 m line spacing. The survey was accomplished
within 9 weeks. The initial AEM data were processed using
the iTEM Fast Approximate transform software developed by
Aarhus University. The inverted data were made available to
Geoscience Australia within 48 hours of completion of each
flight line. This enabled gridding and analysis of data, and
targeting of potential drill sites within 72 hours of data
acquisition. Excellent FiD point comparisons (r2 > 0.8)
provided early confidence in the hydrostratigraphy and water
quality predictions, later confirmed by hydrogeological and
hydrogeochemical analysis of cores recovered from a sonic
drilling program. Preliminary analysis of the datasets has
identified a number of potential MAR targets.
Day 3 Session 3 Stream 2
DEEPER PENETRATION AND GREATER CLARITY
CONSTRUCTION OF A REGIONAL-SCALE 3D
GEOLOGICAL MODEL FROM GEOLOGICALLY
CONSTRAINED POTENTIAL FIELD INVERSION
Robert J. Musgrave* and Stephen Dick
Geological Survey of NSW, Hunter Region, NSW, Australia
[email protected]
Our approach to the generation of a regional 3D geological
model is through potential field inversion of cross-sections.
Wavelet edges form a scaffold on which the major
physical property discontinuities can be linked to yield a
3D model. We have recently completed such a model for
the Koonenberry Belt in far northwest NSW.
The potential field modelling in this process constitutes
a form of lithologic inversion, involving iterative refinement
of parametric bodies. Detailed magnetic and gravity modelling
of structurally complex geology required us to employ complex
polygonal bodies occupying the entire profile. This procedure
contrasts with the statistical approach to lithologic inversion,
which relies on a well-defined geological a priori model as a
seed for random single-voxel iterations. Geological complexity,
limited outcrop, and initial uncertainty between competing
tectonic interpretations precluded construction of such
a starting model for the Koonenberry Belt.
After completion of the 2D inversions, wavelet edges
corresponding to the boundaries of major bodies are identified.
Sets of edges define contours of surfaces, with depth
approximated as half the upward continuation. These surfaces
are linked between corresponding bodies on adjacent sections,
and also serve to extend the model beyond the limits of the
2D inversion.
The completed model for the Koonenberry Belt reveals a
complete assemblage of the elements of a Cambrian arc. The
model predicts features seen on recently reprocessed seismic
sections beyond the areal limits of the original cross-sections.
ASEG-PESA 2010 Conference Handbook
Abstracts
INCREASING CONFIDENCE IN DEPTH IMAGING: CASE
STUDY OF ANISOTROPIC DEPTH IMAGING FROM
AUSTRALIA’S NORTH WEST SHELF
Dominic Fell1, Martin Bayly1* and Llew Vincent2
Perth, WA, Australia
2OMV Australia Pty Ltd, Perth, WA, Australia
1WesternGeco/Schlumberger,
subsurface, the understanding of how these properties change
with chemical alteration provides a powerful tool for deeper
and cheaper exploration.
Day 3 Session 3 Stream 3
FORMATION GEOPHYSICS
[email protected]
A PRACTICAL ROCK PHYSICS MODEL FOR AVO
STUDIES IN CLASTICS AND CARBONATES
This paper demonstrates the increase in confidence of depth
prediction and structural imaging using anisotropic prestack
depth migration of 3D surface seismic data.
Jarrod Dunne
Nexus Energy, Southbank, VIC, Australia
Using examples of both TTI and VTI based anisotropic travel
time derived models updated with hybrid, grid based reflection
tomography, this paper will demonstrate depth imaging with
data from the North West Shelf of offshore Australia.
The dataset contains various types of imaging challenges
including, slow gas affected overburden zones, relatively fast
HRDZ’s (Hydrocarbon Digenesis Replacement Zones), lateral
and vertical changes in interval velocity gradients, fault
“shadows” and volcanic intrusions.
This paper will discuss and demonstrate the necessary pre and
post imaging data conditioning, along with derivation of earth
velocity model and anisotropy functions and their verification.
Anisotropic function derivation will be demonstrated using
well data. Comparisons will be made between data formed
with time domain imaging relative to isotropic and anisotropic
depth imaging.
GEOPHYSICAL SIGNATURES OF CHEMICAL
ALTERATION
Richard Chopping1*, Nick Williams1 and James Cleverley2
1Geoscience Australia, Canberra, ACT, Australia
2CSIRO Exploration and Mining, WA, Australia
[email protected]
The search for mineral deposits below unmineralised cover,
or at depth, requires knowledge of the signatures of chemical
alteration, as well as how these signatures change at depth.
Although not commonly considered in modelling observed
geophysical responses, chemical alteration can have a large
impact on the physical properties of rocks and hence a large
impact on observed geophysical data. Understanding how
chemical alteration influences physical properties is the key to
understanding the geophysical signatures of chemical alteration.
Changes in density, magnetic susceptibility and seismic velocity
due to chemical alteration have been studied. Studies were
performed by examining available physical properties from
mineralised regions, as well as through numerical simulations
of chemical alteration. The changes in these physical properties
allow an understanding of the signatures of chemical alteration
in three key datasets for regional exploration: gravity, magnetics
and seismic reflection. Interpretation of chemical alteration at
both the mine and regional scale is possible with the knowledge
of the changes in physical properties that can result from
chemical alteration.
As property inversions of gravity and magnetic provide
measures of density and magnetic susceptibility in the
ASEG-PESA 2010 Conference Handbook
[email protected]
A rock physics model for typical oil company AvO modelling
and inversion applications would ideally possess the following
attributes: 1) a sound physical basis; 2) as few free variables as
possible; and 3) would predict measured P- and S-wave
velocities for any lithology, porosity, pressure, temperature,
pore-shape and pore-fluid. A formulation based on the doctoral
research of Y. F. Sun into the dynamical theory of fractured
porous media strikes a practical balance between these
attributes, which are to some extent conflicting.
For a known lithology and porefill, the “Sun model” has
only three parameters: porosity, gamma_K and gamma_Mu.
A physical interpretation of the gamma_K and gamma_Mu
parameters can be made by reformulating the original “Sun
model” in terms of the dry rock bulk and shear moduli, where
it becomes clear that they act as interpolators between the Voigt
and Reuss bounds. In doing so, they elegantly bundle the
remaining variables (i.e. pressure, temperature and pore-shape,
to name a few) that, for a given porosity, can act to stiffen or
soften a rock frame. They therefore represent coefficients in
determining the stiffness of the pore-space to impinging
compressional and shear waves.
MULTIPLE ANALYSIS – A BOREHOLE SEISMIC
SOLUTION
Konstantin Galybin*, Sergei Tcherkashnev and Leon Dahlhaus
Schlumberger Australia Pty Ltd, Perth, WA, Australia
[email protected]
Borehole seismic data acquired on wireline or during drilling
have a variety of uses from industry standard corridor stack
and sonic calibration to AVO, Imaging, real-time time-depth
information and pore pressure prediction. This paper presents
a novel workflow that is designed to identify seismic multiple
generators using Vertical Seismic Profiling (VSP). The primary
technique in identification of multiples in surface seismic data
is assessment of periodicity and polarity. Similarly the major
technique in identification of multiples in VSPs is assessment
of the complete VSP wavefield for truncations and periodicities.
In both cases these assessments are made using a qualitative
approach. Now, a more rigorous and structured approach that
involves separation of the multiple energy from the primary
energy is presented. This allows a simpler interpretation and
a quantitative assessment of the relative strengths of primary
reflections and their multiples, which in turn simplifies the
interpretation of the surface seismic data. The results of this
analysis is a list of tops and bottoms of major peg-leg multiple
generator and an image of upgoing multiples. This VSP
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ABSTRACTS
This abstract is published with the permission of the Director,
Geological Survey of NSW, Industry & Investment NSW.
Abstracts
interpretation is transferable to the surface seismic data and
can be used in surface seismic reprocessing to target specific
formations for removal of seismic multiples generated
in these formations.
Day 3 Session 3 Stream 4
These pore stiffness coefficients are claimed to be
independent of porosity, which can be verified using well
log datasets with high quality shear sonics. Applying this
rock physics model to well log data from both clastic and
carbonate environments results in a better fit to the data
than many well known models. The examples also show
that gamma_K and gamma_Mu are not generally equal in
magnitude, which via the “Sun model” equations then implies
that VP/VS ratios are porosity dependent. This challenges the
assumption of linear VP-VS trends that is made in many
seismic amplitude workflows.
MODELLING TENSOR MAGNETIC GRADIENT
RESPONSES OF MARINE CSEM
SEISMIC FACIES ANALYSIS AND RESERVOIR
CHARACTERIZATION BASED ON ISO-TIME
STRATIGRAPHY FRAME
ABSTRACTS
Jianguo Yan*, Qiang Zhu and Shuang Yao
Key Lab of Earth Exploration and Information Technology
(Chengdu University of Technology), Ministry of Education, China
[email protected]
Our study has showed that more accuracy and meaningful
results from seismic facies analysis and reservoir
characterization can be achieved based on iso-time
(geological time-equivalent) stratigraphy frame compared
with the results from time-transgrassive stratigraphy frame.
By comparative researches, we develop and build up our own
seismic analysis and reservoir characterization approaches
under iso-time stratigraphy frame which mainly consists of
(1) identifying the seismic terminations as the top and bottom
of one sequence which is generally identified as 3nd order
sequence (SQ3), (2) reconstructing the seismic volume to
build iso-time frame which will be consistence with sequence
stratigraphy, (3) doing seismic facies volume-analysis in this
new geological time-equivalent frame which will complete
lateral and vertical seismic facies analysis simultaneously and
(4) delineating the detailed inter sequences and the interior
of reservoirs by well log calibration to get final results of 3D
distributions of sedimentary sequences, 3D characteristics
of reservoirs in 3D, etc.
The key technologies we developed and applied are building
new iso-time seismic volume from original seismic volume
by new proportionally flatting technique, and seismic facies
volume-analysis by multi seismic attributes classification.
The proposed approaches have been applied to several studies of
the carbonates reef and shoal reservoir characterization which
has been the big challenge in the seismic interpretation and
reservoir characterization aiming for gas exploration in Eastern
Sichuan Basin due to deeper targets (most around 7000 m in
depth) and lower S/N ratio of seismic data. The results from our
studies have proved that the approaches are valid.
CSEM
David Annetts
CSIRO Earth Science and Resource Engineering, WA, Australia
[email protected]
In recent times, potential field surveys employing tensor
gradiometers have been used in mineral exploration. Some
reasons for this are potential advantages such as improved
resolution, data interpolation, noise suppression and relative
insensitivity to survey orientation. The last two potentialities
are particularly germane to marine CSEM surveys which are
typically sparsely sampled and require processing of measured
fields to ensure that the correct vector component is analysed.
In a series of numerical modelling studies of typical frequencydomain CSEM surveys in both shallow and deep water columns,
this paper shows that tensor gradient measurements have
advantages over conventional CSEM measurements in terms
of target definition especially when survey lines do not fall
over target centres and when traversing near-seafloor bodies
such as gas hydrates.
INTERPRETING CSEM DATA IN COMPLEX RESISTIVITY
REGIME
Lars Lorenz1*, Håkon Pedersen1, Muralikrishna Akella2, Anil Tyagi2,
Pranaya Sangvai2 and Rabi Bastia2
1EMGS ASA, Norway
2Reliance Industries Ltd, Mumbai, India
[email protected]
This case study presents the application of CSEM as a risk
mitigation tool in the Krishna-Goddavari Basin, East Coast
India. A CSEM workflow for application in a portfolio ranking
process is described, ranging from feasibility assessment to
interpretation and post-drilling analysis.
A pre-survey assessment predicted sensitivity to all survey
targets, with depths of 500 m BML to 2000 m BML. The data
interpretation included relative response analysis, unconstrained
inversion and 3D modeling. Relative response variations as well
as unconstrained inversion indicated the presence of local
resistive events. While relative responses showed a lateral
correlation with the prospect areas, additional depth correlation
between resistive events and prospects was derived from the
unconstrained inversion.
To interpret the inversion results, a 3D modeling study was
performed. Premise for the modeling study was the retrieval of
robust anomalies for high – grading as drilling targets, as well
as characterization of possible additional thin resistor events.
Due to limited calibration points for the model, additional
thin resistive events were downgraded until a re-interpretation
with more calibration points could be performed.
The drilling of a CSEM positive prospect at 2000 m BML
yielded commercial hydrocarbons and an additional calibration
point. Using this additional calibration point, a robustness
analysis for the previously downgraded resistors supported
their presence even for models with significantly increased
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ASEG-PESA 2010 Conference Handbook
Abstracts
CONDITIONING OF THE 3D MARINE CONTROLLED
SOURCE ELECTROMAGNETIC INVERSION
Andrew M. Pethick* and Brett D. Harris
Department of Exploration Geophysics, Curtin University, Perth,
WA, Australia
[email protected]
Three dimensional inversion of Marine Controlled Source
Electromagnetic data (MCSEM) data is complex. Achieving
an acceptable outcome in a reasonable time frame requires
considerable manual input to the problem. A short list of
“manual” requirements include: definition of the solution
domain, cell discretisation, weighting of data points, selection of
receiver components, and inclusion of data (e.g. frequencies and
Tx-Rx separations). We proposed methods designed to automate
selection of many of these parameters. Both pre-conditioning
of the problem and feed-back during the inversion process are
used to streamline 3D MCSEM inversion. Automated methods
of establishing the required level of vertical and horizontal
discretisation for the 3D inversion domain are provided. For
example each discretised cell volume can be given by a
weighting based on the level of sensitivity to the acquisition
parameters (e.g. survey geometry). 3D visualisation is used to
help qualitatively examine, original data, inverted data, errors,
conductivities and Fréchet derivatives. The visualised data can
be used to both direct the inversion and understand the success
or otherwise of the outcome. We illustrate how fast approximate
forward solutions used within the typical 3DMCSEM inversion
procedures can trigger the computation of a rigorous solution for
comparison. We demonstrate how automated preconditioning
and iterative analysis of MCSEM data can lead to a more
satisfactory result for 3D inversion.
15:30–17:00
Day 3 Session 4 Stream 1
response tests illustrate the accuracy and lack of numerical phase
anisotropy of the implemented scheme. We apply this approach
to a realistic 3D wide-azimuth synthetic derived from a field
Gulf of Mexico data set. The resulting images demonstrate
the imaging advantages made possible through 3D RWE
implementations, including the improved imaging of steeply
dipping salt flanks, at a reduced computational cost.
SHALLOW WATER DEMULTIPLE
Barry Hung1*, Kunlun Yang1, Joe Zhou1 and Xia Qing Long2
1CGGVeritas, Singapore
2CNOOC Ltd, Singapore
[email protected]
Multiples due to shallow water are commonly observed offshore
Australia such as in Gippsland Basin. These short period multiple
reflections often pose problems to the interpretation of geological
structures. They are not easily handled by conventional surfacerelated multiple elimination (SRME) methods because the
primary water-bottom reflection, which is required by SRME,
is absent in shallow water seismic data due to the near offset
gap. Hence, predictive deconvolution in the x-t or t-p domain
is frequently used for attenuating shallow water multiples.
However, besides multiples, deconvolution also attenuates
primary events that have a periodicity which is close to that
of the water-layer. In this paper, we present a workflow that we
term shallow water demultiple (SWD) for attenuating shallow
water-layer related multiples (WLRMs). SWD is a wavefieldconsistent method that first makes use of WLRMs in the data
to reconstruct the missing water-bottom primary reflection and
then uses the reflection for predicting shallow WLRMs. It is
data driven and takes into account the spatial varying nature
of subsurface structures. Since the WLRM model predicted by
SWD has similar amplitude and phase as the input data, very
short matching filters, which are not possible if deconvolution
is used, can be utilised in the adaptive subtraction process. After
SWD, the other free surface multiples can then be attenuated
using conventional demultiple methods such as SRME.
We demonstrate, through real-data examples, that our workflow
provides an optimal multiple attenuation solution in shallow
water environment in comparison with conventional methods
such as t-p deconvolution or SRME alone.
ADVANCES IN SEISMIC PROCESSING
INLINE DELAYED-SHOT MIGRATION IN TILTED
ELLIPTICAL-CYLINDRICAL COORDINATES
Jeffrey Shragge
Centre for Petroleum Geoscience, UWA, WA, Australia
[email protected]
Riemannian wavefield extrapolation, a wave-equation imaging
method for efficient one-way propagation of 3D wavefields,
is extended to 3D seismic surveys. We formulate an inline
delayed-shot migration procedure in 3D tilted ellipticalcylindrical (TEC) coordinate systems. When inline coordinate
tilt angles are well- matched to the inline source ray parameters,
the TEC coordinate extension affords accurate propagation of
both steep-dip and turning-wave components important for
successfully imaging complex geologic structure. We show
that wavefield extrapolation in TEC coordinates is no more
complicated than propagation in elliptically anisotropic media
easily handled by current finite-difference practice. Impulse
ASEG-PESA 2010 Conference Handbook
IMAGING OF PRIMARIES AND MULTIPLES USING
A DUAL-SENSOR TOWED STREAMER
Norman Daniel Whitmore1*, A. A. Valenciano2, W. Sollner3 and S. Lu4
Houston, Texas, USA
2PGS, Austin, Texas, USA
3PGS, Lysaker, Norway
4University of Texas, Austin, Texas, USA
1PGS,
[email protected]
Multiple reflections are commonly treated as noise in one-way
imaging methods. High effort is put into research and data
processing worldwide in an effort to suppress this source of
noise. In a new perspective multiples are treated as valuable
imaging information. Based on dual-sensor towed streamer
measurement, we decompose the wavefield and apply up/down
imaging of primary and multiple reflections. This approach is
tested using shallow water synthetic data and finally applied on
dual-sensor field data.
AUGUST 2010
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ABSTRACTS
complexity. This motivated the client to allocate additional
resources to review the seismic, upgrading CSEM leads to
prospects.
Abstracts
Day 3 Session 4 Stream 2
DEEPER PENETRATION AND GREATER CLARITY
A NEW METHOD FOR HIGH-RESOLUTION FAULT
IMAGING DELIVERS GROUNDBREAKING INSIGHTS
INTO DRILLING AND PRODUCTION OF RESOURCES
Ralf Oppermann
OPPtimal Exploration & Development Pty Ltd, Wembley, WA,
Australia
[email protected]
ABSTRACTS
Novel techniques and workflows in automated fault extraction
have been developed to visualise faults at extremely high
resolution from 3-D seismic data, and to subsequently integrate
these results with other data to derive fully calibrated fault/
fracture network models for reservoirs.
The results obtained provide a step-change in understanding
drilling and production problems in fields. A focused application
of the new technology workflows can deliver increased
recoveries from reservoirs. And it can result in cheaper, safer
and more successful drilling and mining operations. As such,
the techniques are viewed as Best Practise tools for field
development planning and execution.
Results obtained from studies around the world challenge current
resource industry perceptions:
• Presently, most 3D surveys in the resource industries are
underutilized with respect to the detailed, high-resolution
delineation of faults in the subsurface. The techniques
presented push fault resolution down to the true fault resolution
of a particular data set, not the perceived fault resolution that
is typically established by visual (Interpreter) mapping only.
• The increased fault resolution results in a dramatic increase
in the number of faults that are identified from seismic: e.g.
instead of 20 faults in a field, typically 2 000 are made visible.
• There are way more faults penetrated in wells than realised
industry-wide, and these faults cause a number of drilling
and production problems, or production opportunities,
in compartmentalised, tight, fractured and unconventional
reservoirs, where faults in the subsurface can form fluid
barriers or fluid conduits.
the Kevitsa Ni-Cu deposit in northern Finland is to find areas of
massive sulphide enrichment within a large-tonnage, low-grade
orebody. Since the orebody host is dense olivine pyroxenite, this
compounds the problem of finding dense massive sulphides
within a dense background. For this reason I have concentrated
on the differences between inverted results and the resource
density model. Any positive differences represent previously
unmodelled high density zones, and potential massive sulphide
targets between drillholes. This approach enhances both the depth
of investigation and the effective resolution of the inverted data.
FRACTAL SCALING OF AIRBORNE EM DATA: AN
INDICATOR OF LITHOLOGY AND FLUID CONNECTION?
Tania Dhu1* and Graham Heinson2
Industries & Resources South Australia, Adelaide, SA,
Australia
2University of Adelaide, SA, Australia
1Primary
[email protected]
Electrically conducting fluids within the subsurface account for
a large portion of the Earth’s electrical response and therefore
mapping of groundwater and regions of high salinity can be
undertaken using Airborne Electromagnetic (AEM) methods.
While the majority of near-surface conduction is generally due
to fluids in porous or fractured media, there is always an
ambiguity in determining the cause of the electrical response.
For example, clay layers and mineralization may also
significantly enhance conduction. Analysis of how the Earth’s
resistivity varies with spatial-wavelength through determining
the associated fractal dimension is proposed as an additional tool
that can assist in differentiating anomalies of similar magnitude
but dissimilar sources.
AEM, using the TEMPEST and VTEM systems, has recently
been collected by Geoscience Australia through the Onshore
Energy Security Program over the Pine Creek region in Northern
Territory. Approximately 21 000 line-km of TEMPEST and 9000
line-km of VTEM were collected. A moving window is passed
across each line of data creating small overlapping subsets on
which the fractal dimension is calculated. These values are then
gridded to create a map of the fractal dimension of the Pine
Creek AEM survey data. Such maps are compared with existing
geological and hydrological information allowing for inferences
to be made on the differing sources of anomalism.
HUNTING FOR MASSIVE SULPHIDES BETWEEN
DENSITY LOGS
Day 3 Session 4 Stream 3
Chris Wijns
First Quantum Materials Ltd, Perth, WA, Australia
FORMATION GEOPHYSICS
[email protected]
Gravity measurements are one of the more useful datasets in
the exploration for high-density massive sulphide mineralisation.
However, the fall-off of signal strength with depth limits the
usefulness of surface data alone. Borehole and core density
measurements can be used to constrain surface gravity inversions
and extend their depth of investigation further. The greatest
challenge with incorporating downhole data is the manner
in which these very localised reference measurements are
extrapolated between boreholes. In this study, the geologically
constrained, kriged density model for resource calculations is the
reference model for surface gravity inversions, with appropriate
unweighting away from drillholes. The exploration mandate at
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LEAST-SQUARES INVERSION OF REFRACTION
AMPLITUDES FOR NEAR-SURFACE VELOCITY CONTROL
Alan Meulenbroek
Velseis Pty Ltd, Brisbane, QLD, Australia
[email protected]
Surface-source land seismic surveys contain no uphole control,
hence the velocity of the surface layer is not known. This
parameter is important for the calculation of accurate refraction
statics.
Theoretical expressions have been published for the relationship
between the amplitude of a refraction event and the lithology of
ASEG-PESA 2010 Conference Handbook
Abstracts
This raises the possibility of extracting surface velocity
information from observed first-break amplitudes. Least-squares
inversion of first-break amplitudes can be used to separate each
amplitude into shot, receiver and head-wave coefficient
components. Although the approach is surface-consistent, there
is inevitably some cross-feed between parameters. The primary
practical question is whether the extracted head-wave
coefficients can be reliably interpreted in terms of near surface
velocity contrasts.
The resulting least-squares solution for the receiver term is
compared, quantitatively, to the theoretical expression for
head-wave coefficient. Regularisation is applied to the inverse
problem in the form of a-priori information regarding the range
of offsets over which the theoretical expression can be applied.
Analysis of the singular-value spectrum of the data kernel and
the resolution matrices allow insights into the ease of inversion
and the geological significance of the solution respectively.
AVO ANALYSIS OF A SHALLOW REVERSE POLARITY
IN SYDNEY BASIN
Dariush Nadri*, Sanjeev Rajput, Ben Clennell and Asrar Talukder
CSIRO Petroleum, Perth, WA, Australia
[email protected]
A vast shallow reverse polarity which is extended across the
PEP11 block in offshore Sydney basin and the lack of any wells
in the area has wondered the interpreters about the mechanisms
which has caused such a seismic signature in the area. This
study aims to characterize this reverse polarity using the AVO
analysis and pre stack inversion techniques in a pilot study.
Baleen 2004 2-D towed streamer data are the only recent
seismic data acquired in PEP11 block. Shallow depth water has
left significant amount of multiple energy in shot records. The
presence of a very high velocity sequence of layers which
terminate at the shore line cause a strong ray bending letting
small amount of the energy penetrate to deeper parts. The
reverse polarity reflector is part of a sequence of progradational
sediments which are accommodated at the top of the high
velocity layer.
To characterize the reverse polarity, we have processed 1 second
TWT of two perpendicular lines by preserving the relative
amplitude up to pre stack time migration. Assuming clastic
environment, AVO analysis of the reverse polarity over the lines
shows different signatures across a steep normal fault. The
shallow parts at the up-thrown part of the fault indicate the
wet trend despite different reflectivity strength across the line.
However, the deeper parts correspond to down-thrown shows
the AVO class III. Pre-stack inversion confirms low impedance
in areas with class III and higher impedance in areas which
show the wet trend.
REDUCING UNCERTAINTY IN SEISMIC INTERPRETATION
USING CROSSWELL SEISMIC
Bruno Verduzco, Bruce Marion and Ajay Nalonnil*
Schlumberger, Perth, WA, Australia
[email protected]
Description: Crosswell seismic is an emerging technology which
can provide highly detailed images of the subsurface at the
reservoir scale. The technology has the potential not only to
delineate complex structure but also be used to monitor changes
in the reservoir caused by enhanced recovery strategies.
The technology employs tomographic surveying, whereby the
transmitter and receiver are deployed in separate wells. With this
setup, interwell structure and velocity profiling can be obtained
from reflection processing and direct wave processing
respectively.
Application: In complex plays, traditional interpretation
involving 3D surface seismic combined with log information
retains a large degree of uncertainty since the imaging between
the two scales of information requires in depth geological
knowledge combined with geostatistical best-fit approaches.
With crosswell seismic, the degree of uncertainty when
combining log and surface seismic interpretation is considerably
lower as it represents a physical measurement of sound waves in
depth domain.
Results, Observations, Conclusions: In this paper, an example
of crosswell seismic is discussed where the technology produced
high-resolution images of the geology between wells at 5 to 10
times the resolution of surface 3-D seismic data and revealed
numerous faulted compartments and fault zones in the reservoir
previously obscured in the surface seismic. These results have
lead to a new understanding of the field and improved the well
design process.
Significance of Subject Matter: By having such a measurement in
areas where surface seismic requires more validation, integrating
crosswell seismic into the interpretation workflow presents a new
approach in developing a clearer picture of the subsurface. With
the imaging done between and from well to well at reservoir
scale, all the traditional banes of interpretation are addressed.
Day 3 Session 4 Stream 4
CSEM
3D INVERSION OF TRANSIENT ELECTROMAGNETIC
DATA FROM THE ALVHEIM FIELD, NORTH SEA
Bruce Hobbs1*, Michael Zhdanov2, Alex Gribenko2 and Alan Paterson1
Geo-Services-Em, United Kingdom
2Technoimaging LLC, United Kingdom
1Petroleum
[email protected]
Controlled source electromagnetics may be used as a de-risking
tool to rank potential prospects, as an aid to delineate reservoir
extent and for reservoir monitoring. We present a case history of
transient electromagnetics applied to delineate a North Sea field
culminating in the first 3D inversion of marine time-domain
electromagnetic data.
The survey was conducted in July/August 2008 using a twoship operation and ocean-bottom cables. One ship laid a
ASEG-PESA 2010 Conference Handbook
AUGUST 2010
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93
ABSTRACTS
near-surface layers. The refraction amplitude is proportional to
the shot amplitude and inversely proportional to the offset at
which the refraction is measured. The constant of proportionality
is the head-wave coefficient. Expressions for this term differ
subtly between authors, but the same general trend is observed.
Namely, the head-wave coefficient is inversely proportional to
the velocity contrast between the weathering layer and the
sub-weathering layer.
Abstracts
receiver cable with 30 receiver nodes and a second vessel
placed a source on the sea floor and generated a large amperage
coded transient source. The configuration of the source and
receiver spread resembled that of 2D seismics and the system
was rolled along to obtain multi-fold subsurface coverage. One
section of data spanned 20 km, resulting in measurements at 700
source-receiver locations, and is the subject of this presentation.
The injected current and resulting electric field for each sourcereceiver pair were measured and deconvolved to determine the
earth’s impulse response function. Preliminary independent
inversion of each impulse response was made using 1D models
and the results collated to form a 2D cross-section. This revealed
higher resistivity regions clearly correlating with the known gas
and oil-charged reservoirs. A full 3D inversion using all the data
simultaneously confirmed the general result of the 1D approach
and provided a more detailed description of the resistivity of the
sub-surface.
ABSTRACTS
A CSEM CASE STUDY IN SOUTHEAST ASIA
Syarina Azura Mohamad1*, Lim Toon Hoong1, Lars Lorenz1,
Tan Kian Wei1, Sandeep K. Chandola2, Fatma Nazihah M Khatib2,
Nurul Saadah2, Lee Poh Kin2 and Tayallen Velayatham2
1EMGS Asia Pacific Sdn. Bhd, Singapore
2PETRONAS Carigali Sdn. Bhd, Singapore
[email protected]
This case study presents the application of CSEM as an
important geophysical tool to aid exploration de-risking in a
deepwater acreage in Southeast Asia. A comprehensive imaging
workflow coupled with the integration of seismic and well data
is crucial to successfully interpret CSEM response. The study
area consisted of three prospects identified on the basis of 3D
seismic data covering major part of the acreage. Exploration
targets are expected to occur in the Mid Miocene clastic
formations.
1D modeling was performed using a range of frequencies to
investigate the sensitivity towards the expected targets. The
analysis was then extended to 3D; utilizing all geological and
geophysical information. The pre-survey assessment showed
sensitivity towards the targets.
A tight 3D acquisition grid was adopted for a reliable
measurement of the sub-surface resistivities. Subsequent to data
quality check and basic processing; attribute analysis indicates
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the presence of several resistive events within and outside the
prospect outlines. 1D and 2.5D Inversions were executed to
derive a general background resistivity trend prior to 3D
Inversion. Consistent resistors were recovered from
unconstrained 3D inversion.
The resistivity models from 3D inversion were validated using
3D modeling. Good background models explaining the data in
the calibration area were developed. Additional local thin
resistors were needed to further improve the data-fit.
Good communication between the client and the service provider
has been a key factor in effectively utilizing CSEM data. The
CSEM results obtained from the above analysis provided useful
inputs for firming-up the drilling priority between the prospects.
THE MARINE CSEM RESPONSE OF A SUBMARINE
MASSIVE SULFIDE DEPOSIT
Peter Kowalczyk1*, Lucy Macgregor2 and Nigel Phillips3
Floor Geophysics Inc, Vancouver, BC, Canada
2OHM Ltd, United Kingdom
3Mira Geoscience, Vancouver, BC, Canada
1Ocean
[email protected]
The use of marine CSEM is well established in the offshore oil
industry as a hydrocarbon exploration method. A new and
presently novel use of marine CSEM is to map submarine
massive sulfide (SMS) deposits. However, the optimal
parameters for a CSEM survey being used to map SMS deposits
are quite different from those best suited to hydrocarbon
exploration. SMS deposits are not expected to be buried deeply,
have much smaller dimensions than an oil or gas field, and are
conductive bodies found in volcanic rocks that are more resistive
than the sedimentary rocks of oil and gas fields. Existing CSEM
receivers can be used for ocean mineral exploration, but the
survey parameters will be quite different, with higher
frequencies, lower power transmitters and smaller transmitter
dipoles being used. We have created several realistic scenarios
for subcropping and buried SMS deposits and present the CSEM
responses of these type models using the appropriate frequencies
and system geometries for submarine mineral exploration. The
forward EM modelling algorithm used is the UBC-GIF EH3D
program. The results presented demonstrate the application of
marine CSEM to SMS exploration and assist the selection of
appropriate survey parameters.
ASEG-PESA 2010 Conference Handbook
Abstracts
AEM have considerable potential to elucidate the nature of interaquifer leakage.
8:30–10:30
Day 4 Session 1 Stream 1
IMPROVEMENTS IN GEOLOGICAL MAPPING USING
OPTIMISED AIRBORNE ELECTROMAGNETIC DATA
GROUNDWATER AND SALINITY
[email protected]
KEYNOTE ADDRESS: GUARDING THE LONG-TERM
SUSTAINABILITY OF GROUNDWATER RESOURCES
BY DEFINING AQUIFER CHARACTERISTICS
AND INTER-AQUIFER LEAKAGE USING AIRBORNE
EM TECHNOLOGIES
A number of current airborne electromagnetic systems allow
important system parameters such as waveform, transmitter
moment and receiver delay times to be configured in order to
improve detection of specific geological targets. In most such
systems, however, measurements are made using a set of
‘standard’ measurement parameters which do not necessarily
provide optimal resolution of targets of interest.
T. J. Munday1*, A. Fitzpatrick1, A. V. Christiansen2, V. Berens3,
K. Cahill1 and E. Auken2
1CSIRO, Perth, WA, Australia
2Department of Earth Sciences, Aarhus University, Denmark
3Department of Water, Land and Biodiversity Conservation,
Adelaide, SA, Australia
[email protected]
The sustainable extraction of groundwater resources requires
an understanding of aquifer integrity, geometry and quality,
particularly where it is extracted from confined or multi-layered
systems, and where shallow, unconfined aquifers are too
saline for use either as a source of potable water or for
irrigated agriculture or stock. In such situations, a major
threat to the long-term sustainability of a groundwater
resources is leakage of saline water from formations that
overlie and/or underlie the target aquifers. From a
hydrogeological perspective both situations demand
information on the spatial variations in groundwater quality
and information on surface water-groundwater
interactions.
This paper presents results from an examination of
hydrogeophysics, specifically airborne electromagnetics (AEM)
data acquired by the SkyTEM time domain helicopter EM
system, as a means for improving our knowledge of spatial
patterns associated with inter-aquifer mixing where groundwater
flow is complex. We were particularly interested in the use of
this technology to provide a spatial picture of mixing which
would assist in conceptual hydrogeological model development
and refinement. The study, focussing on the Loxton region in
the Lower Murray of South Australia and considers both
inter-aquifer mixing and surface water-groundwater interaction.
Recent studies in this area provided hydrochemical evidence for
upward and downward leakage between aquifers, and given the
highly saline nature of the lower groundwater system we believe
ASEG-PESA 2010 Conference Handbook
James Reid
Groundprobe, Malaga, WA, Australia
The SkyTEM AEM system is capable of measurements at a
range of transmitter base frequencies from 5 Hz – more than
250 Hz. The system is also capable of collecting interleaved data
at high and low base frequencies over a wide range of delay
times, thereby achieving a large depth of investigation while at
the same time preserving high spatial and depth resolution in the
near surface. The best system parameters for a given exploration
target can be decided by forward modelling based on expected
target properties and dimensions, and on the established noise
levels of the SkyTEM system. An approximate 1-D inversion
can be carried out on SkyTEM field data within a few hours
after the completion of each survey flight, thereby allowing
assessment and further optimization of data acquisition
parameters during the initial stages of a survey. Improvements
in quantitative interpretation of the data achieved by combining
data from multiple transmitter base frequencies and moments are
illustrated using Australian field data examples.
UTILISING AIRBORNE ELECTROMAGNETICS (AEM)
TO MAP KEY ELEMENTS OF THE HYDROGEOLOGICAL
SYSTEM AND SALINITY HAZARD IN THE ORD VALLEY,
WESTERN AUSTRALIA
K. C. Lawrie1, J. Clarke1*, K. P. Tan1, T.J. Munday2, A. Fitzpatrick2,
R. S. Brodie1, C. F. Pain1, H. Apps1, K. Cullen1, L. Halas1, T. J. Kuske1,
K. Cahill 2 and A. Davis3
1Geoscience Australia, Canberra, ACT, Australia
2CSIRO, Water for a Healthy Country Flagship
3Formerly RMIT University, presently Geoscience Australia
[email protected]
The Ord Valley Airborne Electromagnetics (AEM) Interpretation
Project was co-funded by the Australian Government and the
Western Australian Government to provide information in
relation to salinity and groundwater management in the Ord
River Irrigation Area (ORIA). The project area covers the
existing ORIA Stage 1, and the ORIA Stage 2 areas earmarked
for irrigation extension. The project included the acquisition of
5 936 line km of AEM data acquired using the SKYTEM time
domain system.
The SkyTEM AEM system successfully mapped key elements
of the hydrogeological system over most of the project area. In
general terms, the modelled conductivity structure defined from
the SkyTEM smooth model Layered Constrained Inversion
(LCI) matches that defined from available bore data
exceptionally well, with an adjusted R2 = 0.843 determined.
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Day 4: Thursday 26 August 2010
Abstracts
Overall, the AEM survey has provided enhanced spatial
delineation of key elements of the hydrostratigraphy in 3D,
including sand- and gravel-filled palaeochannels, and clay and
silt distribution, as well as salt stores and groundwater quality.
The study found significant areas of high salinity hazard in
several of the Stage 2 areas earmarked for irrigation
development, with salt stores and groundwater salinity often
higher than in the Stage 1 areas.
MAGNETOTELLURIC SURVEYS ACROSS MAJOR
ARCHEAN TECTONIC BOUNDARIES IN SOUTHERN
WESTERN AUSTRALIA
Mike Dentith1*, Shane Evans2, Luis Gallardo1 and Ian Tyler3
University of Western Australia, Perth, WA, Australia
2Moombarriga Geoscience, Perth, WA, Australia
3Geological Survey of Western Australia, Perth, WA, Australia
1The
[email protected]
This study has demonstrated the effective role that AEM
methods can play as part of a ‘hydrogeological systems’
approach to the management of groundwater in existing and
future irrigation developments in Northern Australia. The study
has also demonstrated the potential for ‘calibrated’ AEM
systems and Fast Approximate Inversion software to
significantly shorten AEM project timelines.
Day 4 Session 1 Stream 2
EM & MT: KEEVA VOZOFF SYMPOSIA
ABSTRACTS
K. VOZOFF’S CONTRIBUTION TO LOTEM
Kurt Strack
KMS Technologies, Houston, Texas, USA
[email protected]
Keeva Vozoff became interested in Lotem methods for
hydrocarbons in 1981. His interest then was to prove or disprove
the theoretical work done at Colorado School of Mines and
University of Toronto with respect to detecting thin resistive
layers with grounded dipole EM systems.
With a graduate student (myself) he embarked on writing
numerous proposal to Australian industry to fund the
development of a Lotem system. After several smaller grants, he
received a larger grant from the Australian Government which
allowed him to work with Esso Australia on a survey in Western
Australia. This survey carried out with a mixture of new and old
equipment was the first survey where resistive units were
mapped with surface EM methods. It was second survey in
Australia after a calibration survey in the Sydney basin.
Subsequently, Keeva continued his work mostly in collaboration
with the Lotem group at University of Cologne. This work
culminated in Keeva receiving the Humboldt Prize and spending
a lot of time in Cologne steering an EU project that was focused
of mapping reservoir changes with time. While this project
ended inconclusively it did produce a spinoff Lotem group at the
University of Edinburgh.
Since the emergence of marine CSEM in the early 2000s, it has
become apparent that CSEM can map resistors, which is exactly
as Keeva predicted in 1981. Furthermore, CSEM is can be most
useful if it can be integrated with other methods such as
magnetotellurics and seismics, which is another aspect that
Keeva pioneered. Today marine CSEM is already mainstream
technology while onshore the breakthroughs in operational ease
and reliability are yet to be made.
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The results of two large-scale magnetotelluric surveys in
southern Western Australia are reported. The Balladonia to
Kambalda survey extends across the boundary between the
Archean granitoid-greenstone rocks of the southeastern Yilgarn
Craton and continues on to the adjacent Proterozoic AlbanyFraser Orogen. The second survey extends across the southcentral Yilgarn Craton from Hyden to Norseman.
The Balladonia survey was designed to elucidate the deep
structure of the suture zone between the Archean and Protozoic.
The data show the Albany-Fraser Orogen is largely allochtonous,
having been thrust northwest of the Archean rocks along
detachment structures in the middle and upper crust. The data
allow the location, at depth, of the Yilgarn Craton’s boundary to
be established. There is also evidence for Protoerozic suspect
terrains in the lower crust. The locations of the major crustal
boundaries and major faults has important implications for
nickel and gold mineralisation in the area, both of which are
spatially related to such features.
The Norseman survey crosses greenstone belts (Southern Cross,
Lake Johnston) which are known to be significantly older than
those exposed near Norseman. The survey was designed to
identify any intervening palaeo-suture zone. The survey also
crosses the presumed southern extension of the Ida Fault and
Koolyanobbing shear zones. It is expected to be able to establish
their dip and depth extent. Both are associated with major gold
deposits. These data have only just been acquired but their
quality is very good and initial inversion results are expected
in the few months.
DETAILED MT SURVEYING ON THE WESTERN
MARGIN OF THE MURRAY BASIN TO MAP BEDROCK
STRATIGRAPHIC CONDUCTORS AND COVER
THICKNESS FOR NICKEL EXPLORATION
Graham Jenke
Southern Geoscience Consultants, Belmont, WA, Australia
[email protected]
During an exploration program for nickel associated with mafic
intrusives on the western margin of the Murray Basin, detailed
MT traverses with station spacings down to 250 m were carried
out to search for conductive targets. Although no discrete targets
were identified, the inverted data mapped a stragtigaphic
conductor from outcrop to depth beneath the conductive
sediments of the Murray Basin, and accurately defined the
thicknesses of those sediments.
For sustainable water management, understanding shallow
aquifers and the unsaturated zone is critical. Therefore the
spatial distribution of hydraulic properties is of great interest for
development of accurate recharge distribution models. Logging
of shallow boreholes and measurements made on soil samples
provide an insight into hydraulic properties with depth.
However, they do not provide an adequate image of the spatial
ASEG-PESA 2010 Conference Handbook
Abstracts
Several hundred line kilometres of GPR have been acquired over
the Gnangara Mound. Water retentive layers are easily identified
and differentiated from the regional water table within the GPR
sections. However, it is difficult to constrain the local 3D nature
and the lateral extent of these layers from the very long sparse
2D GPR transects. Small pseudo 3D surveys at key locations
have been completed. We demonstrate how these small pseudo
3D GPR surveys reveal the local consistency of water retentive
layers and how the small high density surveys help understand
the distribution of shallow hydraulic properties along the long
transects.
3-D MAGNETOTELLURIC INVERSION OF 2-D PROFILES:
APPLICATION TO LAND AND MARINE DATA
FOR SHALLOW CRUSTAL INVESTIGATION
Sophie Hautot* and Pascal Tarits
Imagir/iuem, France
[email protected]
The 3-D magnetotelluric (MT) inversion has a great potential for
providing useful information on the geological background
needed in petroleum and mining exploration. We developed a
simple and robust full tensor 3D MT data inversion scheme that
was tested on several real data sets. The technique allows to
provide a detailed 3-D image of complicated geological contexts
such as rift basins beneath thick basaltic screen covers.
However, for practical reasons, 2-D profiles are still carried out
to investigate geological questions. In such cases, tensor
decomposition helps to obtain a local or regional strike which
enable 2-D inversion but static distortion and effects of local and
regional 3-D structures may affect the data. Adhoc static shift
techniques and heavy smoothing techniques are often used to
obtain a reasonable solution but they imply possible bias in the
result. Here, we propose a 3-D inversion approach to interpret
2-D data without any decomposition technique or static
correction required. The 3-D inversion uses the full MT tensor
information in order to recover structures on either side of the
2-D profile. We present results from synthetic tests on 3-D data
acquired along 2-D profiles and applications to land and marine
real data sets. Comparison between a standard 2-D approach and
our local 3-D inversion provides clues about the bias induced by
the static shift correction and 2-D inversion.
Day 4 Session 1 Stream 3
ARCHITECTURE AND DEVELOPMENT OF OFFSHORE
BASINS
BASEMENT ARCHITECTURE AND FORMATION OF
AN OCEAN-CONTINENT TRANSFORM BOUNDARY
OFF WESTERN TASMANIA: INSIGHTS FROM
AEROMAGNETIC AND SEISMIC REFLECTION DATA
COLLECTED FROM A FRONTIER PETROLEUM PROVINCE
George Gibson*, Michael Morse, Cameron Mitchell, Gutam Nayak,
Andrew Stacey and Jennifer Totterdell
Geoscience Australia, Canberra, ACT, Australia
[email protected]
Basement architecture off western Tasmania is a legacy of late
Neoproterozoic-Cambrian subduction-related processes, ocean
basin closure and multiple accretionary events, culminating in
formation of the Delamerian-Ross and western Lachlan orogens.
Structures associated with these fold belts were subsequently
reactivated during late Mesozoic-Cenozoic Gondwana breakup
and the separation of Australia from Antarctica, strongly
influencing the pattern and geometry of offshore rifting,
including formation of an ocean-continent transform boundary
off western Tasmania. Seismic reflection profiles combined with
recently acquired high resolution aeromagnetic data permit this
boundary and its associated reactivated basement structures
(Avoca-Sorell fault system) to be mapped in greater detail than
has hitherto been possible and point to a transform margin
dominated by steeply outward-dipping structures and deep
sedimentary basins similar to other transform margin oceancontinent boundaries, including the highly prospective Côte
d’Ivore-Ghana region off the west African coast. Basement highs
and rotated pre-rift crustal blocks adjacent to the west Tasmanian
transform margin incorporate significant volumes of granite as
well as a lower crust of probable Mesoproterozoic age that is
locally juxtaposed against lower Paleozoic sequences intruded
and/or floored by basaltic and ultramafic material. Aeromagnetic
anomalies sourced from these basement rocks change orientation
from NW- to NE-trending across the Avoca-Sorell fault system
and can be traced laterally into regions of known onshore
basement geology, highlighting both the tectonic significance of
this structure and its origins during lower Paleozoic deformation
accompanying the Delamerian-Ross orogeny.
STRUCTURAL ARCHITECTURE OTWAY AND SORELL
BASINS DERIVED FROM GRAVITY MODELLING
G. K. Nayak*, M. P. Morse, G. M. Gibson, A. R. Stacey and C. H. Mitchell
Geoscience Australia, Canberra, ACT, Australia
[email protected]
The frontier deep-water Otway and Sorell basins are located
west King Island and off the west coast of Tasmania in southern
Australia. These basins developed during Gondwana break-up
when Australia rifted away from Antarctica. 2D and 3D gravity
modelling carried out in conjunction with seismic and geological
interpretation has led to an improved understanding of basement
architecture of the study area. 2D gravity modelling along three
selected seismic lines reveals a N-S crustal scale lineament
extending down to the Moho. A distinct density contrast of
0.16 t/m3 (3.05 t/m3 and 2.89 t/m3) across the structure points
to a significant lithological difference at middle to lower crustal
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ABSTRACTS
variations of key parameters. This may lead to erroneous
assumptions about overall distribution of soil properties. In this
study, we illustrate how Ground Penetrating Radar (GPR) can be
used to image layers that impede the recharge of shallow
aquifers. We discuss some of the different attributes of these
water retentive layers and show how these can be characterized
by Ground Penetrating Radar over the Gnangara Mound, Perth
Basin Western Australia.
Abstracts
depths, interpreted here to reflect a change from dominantly
basaltic to felsic lower crust. This structure is interpreted to be
inherited from a pre-existing basement structure and supports the
hypothesis that the structural evolution of the Sorell Basin was
probably basement controlled. These 2D models are consistent
with basaltic underplating along the margin. The computed 3D
gravitational response of the basin-wide seismic interpretation
correlates moderately well to the observed gravity trend, which
implies consistency between the seismic and gravity data of the
inferred model. This study demonstrates the importance of
integrating multiple geophysical data sets when working in
complex geological environments to validate or invalidate some
geological model.
QUANTIFICATION OF CRETACEOUS-CENOZOIC
EXHUMATION IN THE OTWAY BASIN USING SONIC
VELOCITIES AND IMPLICATIONS FOR HYDROCARBON
EXPLORATION
David R. Tassone, Simon P. Holford and Richard R. Hillis
Australian School of Petroleum, Centre for Tectonics Resources and
Exploration (TRaX), University of Adelaide, Adelaide, SA, Australia
ABSTRACTS
[email protected]
The Otway Basin, southern Australian passive margin, has
experienced a complex Cretaceous-Cenozoic exhumation history
that is primarily caused by mid Cretaceous thermal uplift and
NW-SE oriented-compressional deformation during both the mid
Cretaceous and Miocene-present-day. This exhumation history
has both positive and negative implications for the hydrocarbon
systems of this basin, particularly in terms of the relative timing
of source rock maturation and trap formation. Thus quantifying
the timing and magnitude of exhumation across the basin is
essential for identifying prospective areas and focussing future
exploration in this region.
In order to estimate the magnitude of exhumation across the
Otway Basin we have analysed the degree of overcompaction of
preserved sedimentary units caused by their deeper burial prior
to uplift and exhumation. Although porosity directly describes
compaction state, our approach utilizes sonic velocities that are
widely used as a robust proxy for degree of compaction because
they are strongly dependent on porosity and also because they
are routinely logged in wells.
Sonic velocities of shale units in the Lower Cretaceous Otway
Group, Upper Cretaceous Sherbrook Group and PaleoceneEocene Wangerrip Group from 147 wells distributed across the
entire basin (onshore and offshore, SA and Vic.) have been used
to establish normal burial compaction trends for the basin and
subsequently to estimate differential magnitudes of exhumation
across the basin. This presentation will address the influence that
exhumation has on source rock maturities, reservoir porosities
and velocity/depth conversions in the Otway Basin.
DISTRIBUTION OF VOLCANIC FACIES AND RESULTS
OF POTENTIAL FIELD MODELLING OF THE MENTELLE
BASIN, SOUTHWESTERN MARGIN, AUSTRALIA
Stephen Johnston*, Ron Hackney and Chris Nicholson
Geoscience Australia, Canberra, ACT, Australia
[email protected]
Seismic reflection and gravity potential field data acquired during
the Geoscience Australia SW Margins Survey 2008–09 was used
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to investigate the distribution of volcanic facies and large-scale
structural architecture of the Mentelle Basin, located on the
southwestern margin of Australia. Based on structural differences
the basin is subdivided into the Western (WMB) and Eastern
(EMB) Mentelle Basins. Isopach and seismic facies maps were
used to identify the thickness and distribution of volcanic facies.
These maps show that volcanism is generally confined to the
Western Mentelle Basin, with two distinct areas of thick volcanic
deposits occurring in the central and northern portion.
Two and three dimensional gravity forward models were used to
investigate the structural architecture of the Mentelle Basin. Two
dimensional gravity modelling shows that the crust is extremely
thin in the WMB (c.10 km), associated with two mantle highs.
The crust thickens from the EMB (>20 km) towards mainland
Australia. The two modelled mantle highs coincide with the two
seismically defined areas of thick volcanic deposits.
Analogue models indicate that rift related volcanism is generally
confined to the locus of extension where crustal thinning and
strain are greatest. Thus results of gravity modelling and seismic
interpretation have been interpreted to indicate that Jurassic –
Cretaceous extension was focussed in the WMB. This thinning
of the crust and presence of mantle highs suggests that the
WMB is a failed rift formed during the initial breakup between
Australia and Greater India and abandoned at the onset of
spreading in the Perth Basin.
11:00–12:30
Day 4 Session 2 Stream 1
GROUNDWATER AND SALINITY
UTILISING AIRBORNE ELECTROMAGNETICS
(AEM) TO MAP REGIONAL HYDROSTRATIGRAPHY,
AND KARSTIC AQUIFERS IN THE DALY BASIN,
NORTHERN TERRITORY, AUSTRALIA
K. C. Lawrie1, S. Tickell2, J. Sumner2, Y. Ley-Cooper1, A. Davis1,
M. Costelloe1, K. P. Tan1, L. Halas1 and K. Cullen1
1Geoscience Australia, Canberra, ACT, Australia
2Water Resources Branch, NRETAS, NT, Australia
[email protected]
Dolostone aquifers are a key resource for horticulture and other
developments in the Daly Basin. These aquifers are also a
source of major springs, while the Daly River is considered the
Northern Territory’s most significant groundwater dependent
ecosystem (GDE) due to the presence of large spring activity
providing dry season baseflow. This paper reports on the use of
AEM to map the regional hydrostratigraphy including the Oolloo
Dolostone aquifer and confining layers, and the connectivity and
interaction of the Oolloo Dolostone aquifer with the Daly River.
Regional AEM data (5 km line spacing) was collected as part of
Geoscience Australia’s Onshore Energy Security Program using
the TEMPEST time domain system. A small infill survey (200 m
line spacing) was also acquired over a reach of the Daly River
where major springs had previously been identified.
At a regional scale, the AEM survey has successfully defined
the extent of the Oolloo Dolostone as well as the extent of
overlying (confining) beds. In addition, a new Daly Basin
ASEG-PESA 2010 Conference Handbook
Abstracts
INTEGRATING GROUND PENETRATING RADAR AND
GROUND BASED, HIGH RESOLUTION EM TO IMPROVE
UNDERSTANDING OF FLOODPLAIN DYNAMICS
Michael Hatch1, Ken Lawrie2, Jonathon Clarke2, Philip Mill3,
Graham Heinson1 and Tim Munday4
1Centre for Tectonics, Resources and Exploration, University
of Adelaide, SA, Australia
2Geoscience Australia, Canberra, ACT, Australia
3Geoforce Pty Ltd, Malaga, WA, Australia
4CSIRO Exploration and Mining, Bentley, WA, Australia
[email protected]
We report on results from a coordinated geophysical and drilling
program on highly conductive floodplains near Mildura, Victoria.
High resolution ground TEM (the Zonge NanoTEM system,
configured as a towed rig) and low frequency GPR (the Mala
Pro Ex system, combined with a towed 25 MHz antenna) surveys
were run over three lines to evaluate the effectiveness of near
surface geophysical methods for resolving important floodplain
characteristics, including the depth to water table, location of
perched water lenses, and extent and location of flushed zones
near waterways. We were specifically concerned with whether
the results from the two techniques could be used together to
better inform the hydrogeology of these environments.
The TEM data were processed using standard techniques, i.e.
depth sections were prepared based on smooth-model inversion.
The GPR data were initially processed using standard techniques
to produce wiggle traces. Due to the conductive nature of this
environment and the use of a relatively low frequency GPR
system, the results from the standard processing were not
satisfactory. These data were then reprocessed using conductivity
information from the TEM section to improve velocity estimates
at each GPR sounding. Results show improved resolution of
water table elevation and delineation of river flush zones, while
also providing information about lithological variations in the
unsaturated zone.
In summary, improving velocity estimation by incorporating
information about the conductivity structure of the survey area has
improved the interpretation of GPR data collected in this study,
allowing us to interpret the TEM and GPR data sets together.
AEM SURVEYS OF SALINE WATER INTERFACES
G. J. Street1, R. Miller2 and H. Komberi3
Geoscience Pty Ltd, Perth, WA, Australia
2Fugro Airborne Surveys Pty Ltd, Osborne Park, WA, Australia
3Department of Water, Perth, WA, Australia
1International
[email protected]
Tidal encroachment in areas where groundwater extraction is
high has the potential to cause significant damage to water
resources. Electromagnetic surveys have been used to map saline
ASEG-PESA 2010 Conference Handbook
incursions and time domain airborne electromagnetic surveys
have potential to map the saline wedge in three dimensions.
Four areas along the Pilbara coast were surveyed using
TEMPEST airborne electromagnetic system to evaluate the
potential for groundwater exploitation. As part of this study the
saline interface was interpreted to evaluate potential saline
incursion into the alluvial aquifers.
The results illustrate the difficulties using EM to map the saline
incursion along a regressive coastline. The results show that the
nature of the interface depends upon the evolution of the
shoreline. Regressing shorelines have different saltwater
freshwater interfaces to those of transgressing and static
shorelines. The electromagnetic response of clay rich sediments
in palaeo-lagoonal sediments has an electromagnetic response
similar to that interpreted as due to the wedge of seawater along
the coast. Other data such as digital terrain, airborne radiometrics
and satellite data should be used to interpret the regolith type in
order to distinguish the clay rich lagoon sediments from salt
water in more sandy aquifers along the coast.
Day 4 Session 2 Stream 2
EM & MT: KEEVA VOZOFF SYMPOSIA
ABSTRACTS
formation has been identified by this project in conjunction with
the NT Geol. Survey. This formation overlies the Oolloo
Dolostone aquifer and locally hosts significant aquifers. Both
aquifer systems appear to be hydraulically connected. At a local
scale, the AEM survey has mapped a karstic aquifer
palaeotopography, including areas of spring discharge to the
river. These data should assist with targeting groundwater
resources and targeting sites for monitoring and evaluation.
A drilling program is planned to validate the interpretation.
HIGH RESOLUTION CONDUCTIVITY-DEPTH
TRANSFORMATION OF TEM DATA
Peter K. Fullagar1* and G. A. Pears2
1Fullagar Geophysics Pty Ltd, Brisbane, QLD, Australia
2Mira Geoscience Pty Ltd, Brisbane, QLD, Australia
[email protected]
Conductivity depth transformation of TEM data remains an
important tool for preliminary interpretation, despite the
increasing speed of 1D inversion. Conductivity-depth imaging
(CDI) is very fast, does not require a starting model, and is an
effective means for data quality assessment. Moreover, CDI
sections can serve as starting models for inversion.
This paper describes a high resolution enhancement of an
existing CDI algorithm for TEM data. Conductivity-depth
transformation is accomplished in two steps. Measured voltages
or B-field at a given delay time are firstly transformed to
apparent conductivity. For dB/dt data, the assigned depth, z(t), at
each time is the depth of the electric field or current maximum
(Emax depth) in a half-space with conductivity equal to the
apparent conductivity. For B-field data, the depth to the halfspace B-field maximum (Bmax depth) is employed.
CDI sections based on apparent conductivity provide a vertically
smoothed representation of the true conductivity profile.
Christensen (2002) has shown that the apparent conductivity at
any time can be approximated as an inner product of the true
conductivity with a linear sensitivity function. The sensitivity
function at time t decreases from its maximum value at the
surface to zero at a depth d(t). Therefore, given apparent
conductivities from the CDI algorithm, the smoothing can be
reversed via solution of a simple integral equation. We solve the
integral equation using linear programming. Empirically, we
have found that d(t) c√2z(t).
The implementation of this “sharpened” CDI algorithm is
illustrated on selected examples of synthetic and real airborne
TEM data.
AUGUST 2010
PREVIEW
99
Abstracts
AN AEM SYSTEM CALIBRATION
James Macnae
RMIT University, Melbourne, VIC, Australia
[email protected]
ABSTRACTS
VTEM data was collected over a ground loop laid out near Cape
Naturaliste, WA. The system calibration was determined to be
correct within experimental error. The current induced in the
ground loop and the airborne VTEM response agree within
experimental error to theoretical predictions of amplitude, shape
and decay characteristics from channel 6 onwards. Because the
background response of the ground dominated the early time
channels, it was not possible to exactly quantify the early time
calibration for Channels 1 to 5.
With GPS systems fitted to the airborne loop and the helicopter,
10 bathymetry survey lines were analysed to determine the
statistical variations to be expected in system geometry in
“straight and level balanced flight”. Approximately Gaussian
variances found for geometry parameters imply that the VTEM
system geometry for this specific system could be specified as a
mean value with 95% confidence limits at 2 standard deviations.
The mean geometry and 95% limits for VTEM-24 Tx-Rx
assembly were: 35 (±3) m below and 22 (±4) m behind the GPS
sensor on the tail of the helicopter, displaced 3 (±3) m to port.
Tilted nose down at 5.5 (±6)º and tilted to starboard 1 (±6)º.
The VTEM geometry has been historically quoted as a nominal
40 m below the helicopter altimeter, although some reports have
used a figure of 37 m. This measurement suggests that true
VTEM loop altitudes are in fact somewhat higher than those
delivered in historic data. Correct vertical offset is critical in
quantitative modelling. Further, previously modelled dips of
discrete conductors may need to be adjusted by 5.5º to be
consistent with the systematic loop tilt.
The loop swing in-line (distance behind helicopter) shows a
small energy peak at the 12 sec pendulum frequency, plus
additional effects at longer periods attributed to gradual speed
variations. The loop swing from side-to-side exhibits
a 20–30 sec period, identical to the sideways heli accelerations,
and is hypothesised to be due to controlled pilot steering
adjustments to keep on-line.
NAMIBIA AEM MAPPING: A CASE STUDY OF AIRBORNE
EM DATA USED AS A GEOLOGICAL MAPPING AND
INTERPRETATION TOOL
Barrett Cameron1*, David Hutchins2 and Warwick Crowe1
1Fugro Airborne Surveys Pty Ltd, Perth, WA, Australia
2Geological Survey of Namibia
[email protected]
In 2005 the Geological Survey of Namibia acquired an Airborne
Electromagnetic Survey in North East Namibia. Following
completion of this reconnaissance survey (532 line km), two
areas were selected for detailed survey, namely Elandspan and
Eiseb. In total just over 5 000 line km of AEM were acquired.
Initial qualitative interpretation indicated that the Tempest AEM
System could detect conductors beneath the Kalahari sediments.
Recently a more detailed interpretation has been undertaken, and
many 2D and 3D mapping products generated. Early, mid and
late time EM products were created illustrating the surficial
effects of a river system and a number of deep basement
conductors. The 2D gridded products led to an integrated
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geological interpretation of the area and a depth to basement
surface was constructed from CDI’s. The depth to basement
surface allowed the thickness of the Kalahari sands to be
quantified, increasing the exploration prospectivity in many parts
of the region. Many discrete EM anomalies were also modelled
as discrete plate conductors which allowed the dip and extent of
the conductive strata to be identified. A geological map of the
area, based on these results, has been created in an area with
very little other data coverage and no outcrop. The common
assumption that the Kalahari sands are too deep for further
exploration in the north east of Namibia has been refuted.
Day 4 Session 2 Stream 3
ARCHITECTURE AND DEVELOPMENT OF OFFSHORE
BASINS
MENTELLE BASIN – A RESULT OF THE COMBINED
EXTENSIONAL HISTORY OF THE SOUTH-WESTERN
AND SOUTHERN AUSTRALIAN MARGINS
Irina Borissova1*, Barry Bradshaw2, Chris Nicholson1, Danielle Payne1,
and Heike Struckmeyer1
1Geoscience Australia, Canberra, ACT, Australia
2CO2 Geological Storage Solutions, Canberra, ACT, Australia
[email protected]
New geophysical data acquired by Geoscience Australia during
the Southwest Margins 2D seismic survey in 2008–09 has been
used to interpret the tectonic and depositional history of the
Mentelle Basin. The Mentelle Basin is a large, potentially
prospective frontier basin located between the Yallingup Shelf
and the Naturaliste Plateau. It comprises several intermediate
water-depth depocentres (500–1500 m) in the east (eastern
Mentelle Basin) and a large ultra deep-water depocentre
(3000–3500 m) in the west (western Mentelle Basin).
Interpretation of the new data revealed that initial rifting in the
Mentelle Basin occurred in the Early Permian as part of the
Perth Basin extensional system. This was followed by Late
Permian to Early Jurassic thermal subsidence. Half-graben
structures with Permo-Triassic fill have been mapped in the
eastern Mentelle Basin. The main depositional phase in the
western Mentelle Basin has been interpreted to correlate with
Late Jurassic to Early Cretaceous extension in the Perth Basin
and on the Southern Margin. New structural interpretation shows
that in the northern part of the western Mentelle Basin, major
structures are trending N-S similar to the Perth Basin, whereas
in the south most structures are trending SW-NE, which is
consistent with the orientation of the extensional basins on the
Southern Margin. The proximity of the Southern Margin rift
system not only affected the structure of the Mentelle Basin but
also resulted in major fault reactivation, inversion and margin
collapse in the Eocene corresponding to the onset of fast
spreading in the Southern Ocean.
STRUCTURE STYLES AND TECTONIC EVOLUTION
OF THE ABROLHOS SUB-BASIN, PERTH BASIN,
WESTERN AUSTRALIA
Shanyin Liu1*, Paul Lennox1 and Nigel T. Jones2
1School of Biological, Earth and Environmental Sciences,
The University of New South Wales, Sydney, NSW, Australia
ASEG-PESA 2010 Conference Handbook
Abstracts
Oil Company Ltd, Sydney, NSW, Australia
[email protected]
Based on examination and re-interpretation of 2D seismic and
well data, three groups of faults were recognized in the Abrolhos
Sub-basin: (a) major normal faults transecting the Permian,
Triassic and Jurassic, (b) small normal faults developed in the
Early Permian, and (c) small normal faults developed in the
Triassic and Jurassic.
The major faults usually have large offsets and strike northnorthwest. Most of these are at intra-basin boundaries,
subdividing the area into an eastern margin, an eastern graben,
an eastern horst, a central depocentre, a western horst and a
western graben. Mostly these trend north-north-west, except for
the eastern horst, which trends north-south and extends
southward to join the western horst.
Some small faults developed in the Early Permian. They usually
dip east and show strong syn-depositional character, indicating
block rotation. These faults terminate at the Late Permian
Unconformity. Other small faults developed in the Triassic and
Jurassic. They usually dip west. These late faults and the major
faults terminate at the Early Cretaceous Unconformity.
The Abrolhos Sub-Basin has undergone two main rifting stages.
In the Early Permian the basin was initiated under east-northeast
– west-southwest extension, resulting in development of northnorthwest striking normal faults. During the Jurassic, northwestsoutheast extension commenced. The oblique extension resulted
in re-activation of some pre-existing north-northwest striking
faults and generation of new strike-slip faults. Each rifting stage
was followed by basin inversion due to the break-up of
Gondwana. This resulted in regional uplift and formation of the
two key regional geological boundaries: the Late Permian
Unconformity and the Early Cretaceous Unconformity.
CHALLENGES IN THE USE OF POTENTIAL FIELD DATA
FOR STUDIES OF REMOTE, DEEP WATER FRONTIER
BASINS
Ron Hackney*, Michael Morse and Stephen Johnston
Geoscience Australia, Canberra, ACT, Australia
[email protected]
Gravity and magnetic data are important to Geoscience
Australia’s efforts to provide pre-competitive information to
reduce exploration uncertainty in offshore frontier basins. These
efforts predominantly rely on data from satellite altimetry and
ship measurements. Satellite-derived gravity datasets have
near-global coverage, but their resolution and accuracy is
limited. Ship measurements provide ideal resolution, but the use
of ship-borne data is often limited by sparse ship-track coverage
and extreme water depths.
The extensive coverage provided by gravity datasets derived
from satellite altimetry is useful for first-pass interpretation of
frontier basins and planning of more detailed marine surveys.
However, inconsistencies between different satellite altimetry
datasets and new ship-borne data from Geoscience Australia’s
Southwest Margins Survey highlight the need for caution when
using satellite-derived data and the importance of ship-based
(or airborne) data.
Australia where various generations of data have recently been
levelled). The extreme depth of some frontier basins is also a
limiting factor. For example, anomaly amplitudes associated
with the deep-water Mentelle Basin are comparable to
measurement error.
The coverage of gravity and magnetic data in Australia’s marine
jurisdiction will continue to improve through new marine
surveys, hopefully including those using dedicated, full-time
instruments proposed for Australia’s new Marine National
Facility vessel. Airborne surveys that cover Australia’s shelf
areas should also be seriously considered.
13:30–15:00
Day 4 Session 3 Stream 1
GROUNDWATER AND SALINITY
SURFACE WATER-GROUNDWATER EXCHANGE
IN TRANSITIONAL COASTAL ENVIRONMENTS
BY AIRBORNE ELECTROMAGNETICS: THE VENICE
LAGOON EXAMPLE
ABSTRACTS
2ROC
Andrea Viezzoli1* and Pietro Teatini2,3
1Aarhus Geophysics ApS, Denmark
2Department Mathematical Methods and Models for Scientific
Applications, University of Padova, Italy
3Institute of Marine Sciences, CNR, Venice, Italy
[email protected]
A comprehensive investigation of the exchange between surficial
waters and groundwater in transitional environments, and hence
the mixing of waters characterized by a different salt
concentration, is an issue of paramount importance considering
the ecological, cultural, and socio-economic relevance of
transitional environments. Acquiring information, which can
improve the process understanding, is often logistically
challenging, and generally expensive and slow in these areas.
This applies both for punctual, invasive borehole measurements
as well as for ground-based non invasive geophysical surveys.
Here we investigate the capability of airborne electromagnetics
(AEM) to give a significant contribution to the understanding of
the hydrogeology within, below and at the margin of the Venice
Lagoon, Italy. The quasi-3D modelling of the SkyTEM data by
the spatially constrained inversion (SCI) methodology allows to
accurately distinguish several hydrogeological features, both
underneath the lagoon and the farmland beside it.
Hydrogeological features resolved are, for example, the extent
of the saltwater intrusion in coastal aquifers and the transition
between the upper salt saturated and the underlying fresher
sediments below the lagoon bottom. While the AEM data show
a high degree of coherence with available ancillary information,
both form wells and from other geophysical techniques, they
improve greatly the understanding of the hydrogeology in the
Venice lagoon, both at large scale and in details. The research
highlights the great potential of AEM to improve significantly
the hydrogeological characterization of subsurface processes in
lagoons, wetlands, and deltas worldwide.
Despite the resolution advantages of surface data, levelling in
frontier regions is often only possible where ship-track density
is sufficient (e.g. the frontier Capel and Faust Basins off eastern
ASEG-PESA 2010 Conference Handbook
AUGUST 2010
PREVIEW
101
Abstracts
QUANTITATIVE HYDROGEOLOGICAL FRAMEWORK
INTERPRETATIONS USING HELIBORNE
ELECTROMAGNETIC SURVEYS FOR THE NORTH PLATTE
VALLEY, WESTERN NEBRASKA GROUNDWATER MODEL
Jared Abraham*, James Cannia, Steven Peterson, Bruce Smith, Burke
Minsley and Paul Bedrosian
US Geological Survey, Denver, USA
ABSTRACTS
[email protected]
Increasingly complex groundwater management requires more
accurate hydrogeologic frameworks for groundwater models used
in resource management. These complex issues have created the
demand for innovative approaches to data collection. In
complicated terrains, groundwater modelers benefit from
continuous high-resolution geologic maps and their related
hydrogeologic-parameter estimates. The USGS and its partners
have collaborated to use airborne geophysical surveys for
near-continuous coverage of areas of the North Platte River valley
in western Nebraska. The objective of the surveys was to map the
aquifers and bedrock topography of the area to help improve the
understanding of groundwater-surface water relations to be used
in water management decisions. Frequency-domain helibourne
electromagnetic (HEM) surveys were completed, using a unique
survey flight line design, to collect resistivity data that can be
related to lithologic information to refine groundwater model
inputs. To make the geophysical data useful to multidimensional
groundwater models, numerical inversion is necessary to convert
the measured data into a depth-dependent subsurface resistivity
model. This inverted model, in conjunction with sensitivity
analysis, geological ground truthing (boreholes), and geological
interpretation, is used to characterize hydrogeologic features.
The interpreted two and three dimensional data provides the
groundwater modeler with a high-resolution hydrogeologic
framework and a quantitative estimate of framework uncertainty.
This method of creating hydrogeologic frameworks improved the
understanding of the actual flow path orientation by redefining
the location of the paleochannels and associated bedrock highs.
The improved models represent the actual hydrogeology at a level
of accuracy not achievable using previous data sets.
GROUND-PENETRATING RADAR TO RESOLVE WATERRETENTIVE LAYERS FOUND ON THE GNANGARA
MOUND, WA
Elmar Strobach1*, Brett D. Harris1, Christian J. Dupuis1, Michael Martin2
and Anton W. Kepic1
1Curtin University, Perth, WA, Australia
2Water Corporation, Perth, WA, Australia
[email protected]
For sustainable water management, understanding shallow
aquifers and the unsaturated zone is critical. Therefore the
spatial distribution of hydraulic properties is of great interest for
development of accurate recharge distribution models. Logging
of shallow boreholes and measurements made on soil samples
provide an insight into hydraulic properties with depth.
However, they do not provide an adequate image of the spatial
variations of key parameters.
This may lead to erroneous assumptions about overall
distribution of soil properties. In this study, we illustrate how
Ground Penetrating Radar (GPR) can be used to image layers
that impede the recharge of shallow aquifers. We discuss some
of the different attributes of these water retentive layers and
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show how these can be characterized by Ground Penetrating
Radar over the Gnangara Mound, Perth Basin Western Australia.
Several hundred line kilometres of GPR have been acquired over
the Gnangara Mound. Water retentive layers are easily identified
and differentiated from the regional water table within the GPR
sections. However, it is difficult to constrain the local 3D nature
and the lateral extent of these layers from the very long sparse
2D GPR transects.
Small pseudo 3D surveys at key locations have been completed.
We demonstrate how these small pseudo 3D GPR surveys reveal
the local consistency of water retentive layers and how the small
high density surveys help understand the distribution of shallow
hydraulic properties along the long transects.
Day 4 Session 3 Stream 2
EM & MT: KEEVA VOZOFF SYMPOSIA
HIGH RESOLUTION VERSATILE TIME DOMAIN
ELECTROMAGNETIC (VTEM) SURVEY FOR COPPER
GOLD MINERALISATION IN THE NARACOOTA
VOLCANICS OF WESTERN AUSTRALIA
Matthew Cooper
Resource Potentials, Perth, WA, Australia
[email protected]
Alchemy Resources have flown a large, high resolution Versatile
Time Domain Electromagnetic (VTEM) survey over their
Naracoota Copper-Gold Project in Western Australia. The
project area includes the prospective Naracoota Volcanic rocks,
which host the recent Degrussa Cu-Au discovery by Sandfire
Resources, which lies along strike to the north east.
In contrast to what may be considered conventional, the VTEM
survey parameters were specifically selected to allow
oversampling of data across lines by collecting data on 100 m
spacings and acquiring both the Z and X (dB/dt and B-Field)
components to allow better delineation, definition and targetting
of conductors. The close line spacing and inclusion of the
X-Component data has resulted in conductors being detected that
that may have been missed or overlooked if only the
Z-Component data was acquired. The collection of the
X-Component has also provided additional discrimination when
completing conductivity depth inversions and modelling.
A cost saving benefit of the high resolution survey parameters
employed and processing completed on the data, has been the
ability to directly drill target conductors without the need for
completing follow up ground based surveys.
This paper reviews and evaluates the results from the VTEM
survey highlighting gains that can be made through high
resolution data collection, innovative processing and modelling
to directly drill target conductors.
A GLOBAL MEASURE FOR DEPTH OF INVESTIGATION
IN EM AND DC MODELING
Anders Vest Chritiansen1* and Esben Auken2
1Geological Survey of Denmark and Greenland, Denmark
2Hydrogeophysics Group, Aarhus University, Denmark
[email protected]
ASEG-PESA 2010 Conference Handbook
Abstracts
The method is based on the actual model output from the
inversion and includes the full system response, contrary to
assuming e.g. planar waves over a homogeneous halfspace.
Equally important, the data noise and the number of data points
is integrated in our calculation. Our methodology is based on a
recalculated sensitivity (Jacobian) matrix of the final model and
it can thus be used on any model for which a sensitivity matrix
can be calculated.
Contrary to other sensitivity matrix methods we define a global
and absolute threshold value contrary to defining a relative, say
5%, sensitivity limit.
In regions with significant sensitivity the DOI will depend
strongly on data. However, in regions with small sensitivities,
the model is determined by the regularization, the reference
model or other constraints. Hence, the DOI separates model
areas of data dependent information from regularization and
inversion dependent information.
Interpreting a final image with the DOI superimposed is more
reliable than using the model alone and the DOI is directly used
to blank information on sections, interval resistivity maps, etc.
Day 4 Session 3 Stream 3
ARCHITECTURE AND DEVELOPMENT OF OFFSHORE
BASINS
REVISED PLATE TECTONIC HISTORY OF THE WEST
AUSTRALIAN MARGIN REVEALS HOW THE GASCOYNE
TERRANE DOCKED AT WEST BURMA
Ana Gibbons*, Joanne Whittaker and Dietmar Muller
University of Sydney, NSW, Australia
[email protected]
Southeast Asia contains various continental fragments that
sequentially rifted from East Gondwana. East Gondwana’s
fragmentation was initialised with Late Jurassic rifting along
the northwest Australian margin, forming the Argo Abyssal
Plain, and followed by Early Cretaceous N-S oriented rifting
along the entire western Australian margin, forming the
Gascoyne, Cuvier and Perth Abyssal Plains. In a
comprehensive study to address the issue of margin formation
and terrane drift and docking, we revised the tectonic
formation of the entire margin using an integrated analysis of
marine magnetic and gravity anomaly data from all abyssal
plains involved.
Our model highlights the necessity for a new continental
fragment, the Gascoyne Terrane, due to the presence of
tectonic features, such as margin age offsets, spreading rates,
ridge jumps and isochron orientations, that are distinctly
different north and south of the Wallaby Zenith Fracture Zone
(WZFZ). Our model suggests that the northern extent of Greater
ASEG-PESA 2010 Conference Handbook
India was limited by the WZFZ. The relative motion between
Greater India and Australia formed the Perth Abyssal Plain,
while motion of the Gascoyne block, located north of the
WZFZ, formed the Cuvier and Gascoyne Abyssal Plains.
Following rifting from the northwest margin north of the
Exmouth Plateau, Argoland accreted to Burma at ~75 Ma. Our
model suggests that the Gascoyne Terrane was accreted to West
Burma at ~55 Ma, following about 20 million years of Tethys
seafloor subduction after Argoland’s accretion, and that the
eastern tip of Greater India also collided with West Burma at
around 35 Ma.
TECTONICS AND DIRECTION OF BLOCK MOVEMENT
IN THE NORTHEASTERN SOUTH CHINA SEA
Chen Jie1*, Zhong Guang-jian1 and Liu Shaohua2
Marine Geological Investigate Bureau, Guangzhou,
China
2Institute of Geology and Geophysics, Chinese Academy
of Sciences, China
1Guangzhou
[email protected]
Based on the characteristics of geology and geophysics, five
structural sections were distinguished in the northeastern South
China Sea: AB section is a stretching area of the continental
shelf; BC section is the expanded area of the continental slope,
with many pull-apart basins; CD section is the deep sedimentary
basin with weak compression and deformation. The extensional
basins of the continental slope subducted underneath this section
shallowly. The western deep-sea sedimentary basins was
elevated, and inclined eastward; DE section is a strongly
compressed sedimentary basin zone with stronger squeezing in
the eastern part. The weak-deformed deep-sea sedimentary basins
subducted shallowlyunderneath this section, and were lifted up in
the western region. The east of E is the tectonic belt of LuzonTaiwan island arc, and is a steady rigidity block. Under the
eastern or southeastern uniform stress field, the northeastern part
of the South China Sea underwent different stress state and
formed unique structure patterns in South China Sea: extensionalweak compressive-strong compressive from north-west to east.
Two shallow subduction zones were recognized in the seismic
profiles. All the tectonic blocks have accordion-folds-style
structures and converged in the east, with stronger folding near
the Philippine island of Luzon arc-Taiwan Island. From west to
east sedimentary basins showed different stages of the basins
development: growth, mature and terminations. Block subduction
and regional block inclining directions were all aligned with the
directions of the regional stress field.
GEOPHYSICAL DELINEATION OF VOLCANICS AND
INTRUSIVES OFFSHORE NW AUSTRALIA USING
GLOBAL ANALOGUES
Max Rohrman
Woodside Energy, Perth, WA, Australia
[email protected]
The northwestern margin of Australia is a prolific hydrocarbon
province, with large parts affected by volcanism and igneous
intrusions, such as the outer Exmouth and Browse basins as well
as parts of the Canning Basin. Volcanic features have on various
occasions been mistaken for valid prospects, that have
subsequently been drilled with disappointing and costly results.
Proper delineation of volcanic constructions is therefore crucial
AUGUST 2010
PREVIEW
103
ABSTRACTS
All geologists or geophysicists want to know the depth of
investigation (DOI) for their final survey models. For diffusive
methods, such as groundbased or airborne EM, there is no
specific depth below which there is no information on the
resistivity structure, but the question is to what depth the model
is most reliable. We present a new robust concept for the
calculation of DOI that is valid for any 1D EM geophysical
model.
Abstracts
ABSTRACTS
in exploration efforts especially with current NW shelf
exploration progressing in deeper water closer to the continentocean boundary. Most volcanics on the northwest shelf consist
of doleritic intrusions, volcaniclastics and basalt flows. Normally
these volcanics show a sharp contrast on seismic data due to
their high impedance resulting in bright amplitudes on the
seismic stack. The high impedance contrast of volcanics also
contributes to seismic imaging problems below the volcanic
flows or intrusions, this becomes more evident when basalt
flows thicken as evidenced on the North Atlantic margin. A
simple solution to this problem is to filter seismic data for lower
frequencies, since lower frequencies more easily penetrate thick
volcanic sequences, while the higher frequencies are scattered.
Another common imaging problem is interbed multiple
generation due to the high impedance of the volcanics. When
volcanics have been exposed to significant weathering and
subsequent burial, impedance values are lowered, making it
more difficult to distinguish them from clastic rocks. Larger
volcanic features such as igneous complexes and volcanoes, can
mimic antiformal structures on seismic data, but can be easily
de-risked by integrating gravity and magnetic data, especially by
using data filtering techniques. Submerged volcanoes might be
prospective due to reefs growing on top of them as evidenced by
examples from western India.
15:30–16:30
Day 4 Session 4 Stream 1
GROUNDWATER AND SALINITY
TIME-LAPSE MONITORING OF A SALINE
GROUNDWATER PLUME USING ELECTRICAL
GEOPHYSICAL METHODS
Tristan Campbell
Geoforce, Perth, WA, Australia
Day 4 Session 4 Stream 2
EM & MT: KEEVA VOZOFF SYMPOSIA
SKYTEM SYSTEM CALIBRATION: TWO SYSTEMS ONE
DATASET
Aaron Davis1*, Yusen Ley-Cooper2 and Casper Kirkegaard
1RMIT University, Melbourne, VIC, Australia
2Geoscience Australia, Canberra, ACT, Australia
As part of the Broken Hill Managed Aquifer Recharge Project,
established by the Australian Government to secure Broken
Hill’s water supply, the largest AEM survey in Australia to date
was commissioned to delineate potential managed aquifer
recharge and groundwater resources in the Darling Floodplain
near Menindee, New South Wales.
The survey involved the use of two separate SkyTEM helicopter
airborne electromagnetic (AEM) systems collecting data
simultaneously. In order to ensure data consistency between the
two systems, the Danish example of using a hover test site to
calibrate the AEM data to a known reference is followed. Since
2001, Denmark has been using a national test site for all
time-domain electromagnetic (TEM) instruments that are used
there, including the SkyTEM system. The Lyngby test-site is
recognised as a well-understood site with a well-described
layered-earth structure of 5 layers. The electrical structure of site
acts as the accepted national model, and all instruments are
brought to it in order to produce consistent conductivity results.
Using a ground-based TEM system which was calibrated at the
Lynby test site, we operate the same instrument at our selected
site in the Broken Hill project area. Using information of the
instrument (i.e., waveform, filters, timing of receiver chanells),
we produce a layered-earth model that becomes the accepted
model for the two AEM systems. After the hover test, an
appropriate time shift and amplitude scaling is applied to each
AEM system to ensure that both systems produce seamless
conductivity maps upon inversion.
[email protected]
With increasingly stringent environmental conditions on
operating licenses for industrial plants, the need for accurate
monitoring of groundwater has become an important
consideration for many companies. From 2004 to 2009, a variety
of electrical geophysical methods have been deployed at Coogee
Chlor Alkali’s Kemerton plant site (north of Bunbury in Western
Australia) to monitor the extent and conductivity of a known
saline groundwater plume originating from the plant site.
Geophysics has been applied on an annual, ongoing basis for
this objective and included electromagnetic conductivity
mapping, Electrical Resistivity Imaging (ERI) and downhole
logging (conductivity and gamma). These data have been
analysed in conjunction with groundwater salinity data from
monitoring boreholes and shown a marked decrease in the extent
and conductivity of the saline plume from commencement of
surveys to date. This correlates with the construction of a new
salt dissolver system in 2005, the old one of which was thought
to be the main contributor to increased levels of groundwater
salinity originating from the plant. Whereas the borehole
sampling regime provided Coogee with confirmation that the
conductivity of the groundwater was decreasing, the geophysics
was able to confirm that the boreholes were sampling the main
body of the conductive plume and confirm that extent, as well
as conductivity, of the plume was decreasing from year to year.
104
PREVIEW
AUGUST 2010
MAGNETOTELLURIC RESULTS ALONG THE N-S
CURNAMONA SEISMIC TRAVERSE TO THE EAST
OF LAKE FROME, SOUTH AUSTRALIA
Peter R. Milligan1 and F. E. M. Lilley2
1Geoscience Australia, Canberra, ACT, Australia
2Australian National University, Canberra, ACT, Australia
[email protected]
Magnetotelluric data were acquired for Geoscience Australia by
contract along the north-south 08GA-C1-Curnamona seismic
traverse to the east of Lake Frome from November 2008 to
January 2009 as part of the Australian Government’s energy
security initiative. Twenty five sites were spaced an average of
10 km apart, and five-component broadband data were recorded
with a frequency bandwidth of 0.001 Hz to 250 Hz and dipole
lengths of 100 m. Industry standard EDI data files were supplied
to Geoscience Australia, and provide the traditional frequency
components of the magnetotelluric tensor and magnetovariational
response functions for analysis.
Apparent resistivity and phase plots are presented, along with
dimensional analyses of the data based on rotational invariants,
the representation of the data by the phase tensor, and Parkinson
arrows. These analyses provide insight into the complexity of
ASEG-PESA 2010 Conference Handbook
Abstracts
1D and 2D crustal conductivity models of the data have been
generated; these results are discussed in terms of possible
conducting mechanisms and are also compared with
interpretations of the traverse based on seismic, potential field,
drill-hole samples and other data.
provides evidence that the Wallaby Plateau is partially
composed of thick sedimentary stratigraphy, and lends some
support for the hypothesis that parts of the Plateau are underlain
by extended continental crust beneath a carapace of volcanics.
Thus variable velocity-structure characteristics have potential
implications for petroleum prospectivity on the Wallaby
Plateau.
Day 4 Session 4 Stream 3
3D GOUSSEV FILTER: A SIGNAL SEPARATION AND
EDGE DETECTION FILTER APPLIED TO AEROMAGNETIC
DATA OVER THE GREAT AUSTRALIAN BIGHT
ARCHITECTURE AND DEVELOPMENT OF OFFSHORE
BASINS
Barrett Cameron1* and Serguei Goussev2
1Fugro Airborne Surveys Pty Ltd, Perth, WA, Australia
2Fugro Gravity and Magnetic Services
SEISMIC VELOCITY STRUCTURE OF THE WALLABY
PLATEAU AND IMPLICATIONS FOR ITS GEOLOGY
AND EVOLUTION
[email protected]
Alexey Goncharov, Gabriel Nelson* and Phil Symonds
Geoscience Australia, Canberra, ACT, Australia
[email protected]
In 2008/2009, as part of the Offshore Energy Security Program,
Geoscience Australia conducted a contract seismic reflection
survey to examine the geology and petroleum prospectivity of
the enigmatic Wallaby Plateau. Five seismic lines were acquired
across it using an 8 km solid streamer and a 4290 cubic inch
airgun array. Analysis of stacking velocities from this survey
identified areas where velocities are well constrained down to
at least 7–8 s two-way time. The stacking-derived interval
velocities were smoothed and compared with the seismic
reflection imagery to understand variations in velocity structure
across the Plateau, and gain insight into the geological
characteristics of major distinct seismic packages, e.g. divergent
dipping reflectors. In some cases velocity structure correlates
well with the reflectivity pattern, and in other cases it cuts
across it. Different velocity-structure characteristics are likely
to be associated with either predominantly sedimentary or
predominantly magmatic lithology due to differences in original
physical properties combined with compaction differences
between these lithologies. This analysis, along with
comparisons to drilled sedimentary packages in the northern
Houtman Sub-basin and similar continental margins worldwide,
ASEG-PESA 2010 Conference Handbook
Aeromagnetic data was acquired for the Great Australian Bight
client project over the Ceduna Basin and many derivative
products were generated to enhance the magnetic data prior to
interpretation. The shallower sections of the basin were
enhanced very well with Tilt Derivative filters, Vertical
Derivative filters and the Goussev filter. These routine magnetic
grid derivatives were less effective in the deeper parts of the
basin. Jacobsen Filtering was trialed to create residual products
to preserve the signal necessary for further enhancement. A new
filter was constructed to provide the best enhancement of the
magnetic data for boundary detection in the deepest parts of the
Basin. This “3D Goussev Filter” is a combination of running the
Goussev Filter on pseudo-slices of the magnetic signal. These
pseudo-slices were created by second order Jacobsen Filtering;
subtracting successive Upward Continued Residual grids from
each other in a stepped methodology. The 3D Goussev Filter
illustrated excellent edge detection from the zero contours of the
second order residual products and gave an extrapolation into
the depth dimension based on the mathematics of the Upward
Continued filter. These qualitative products aided in the 3D
visualization of the magnetic signal as well as detection of major
basement controlling structures. The 3D Goussev Filter separates
the super-positioning effect in potential field data to detect edges
and boundaries with pseudo-depth. It is postulated that this
technique of signal processing would be equally effective with
gravity and gravity gradient data.
AUGUST 2010
PREVIEW
105
ABSTRACTS
the Earth conductivity giving rise to the MT responses and are
a useful precursor to modelling.
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