MGLS Multiwell Analysis Paper

Multiwell Analysis of Downhole Physical Rock Properties of
Kimberlite: Guacho Kuĕ, Northwest Territories
Susanne MacMahon 1, Senior Geoscientist, Earthfx Inc., Toronto, Ontario
Chris Wallace 2, Senior Geophysicist, Debeers Canada Exploration, Yellowknife, NWT
Dirk Kassenaar 3, Director of Application Development , Viewlog Systems, Toronto, Ontario
Bill Morris 4, Professor, McMaster University, Hamilton, Ontario
MacMahon S. E., Wallace C., Kassenaar D.J., Morris W.A., Multiwell Analysis of
Downhole Physical Rock Properties of Kimberlite: Guacho Kuĕ, Northwest Territories,
in Proceedings of the 8th International KEGS/MGLS Symposium on Logging for Minerals
and Geotechnical Applications, Toronto 21-23 August 2002
Abstract
Kimberlite pipes commonly comprise a number of different lithological phases.
How these individual phases interrelate to one another often has major economic
significance. If the individual lithological classes have distinct physical properties then it
should be possible to construct a geophysical model that describes the internal
morphology of each kimberlite pipe.
Multiparameter borehole geophysical measurements were collected from 71 boreholes, at
the Guacho Kuĕ property in the Lac de Gras area, Northwest Territories. Four pipes
surveyed in this study are; 5034, Hearne, Tuzo and Tesla. Measurements were made with
the following tools; Natural Gamma, Neutron-Neutron, Gamma-Gamma, Inductive
Conductivity, Spontaneous Potential, Point Resistance, Magnetic Susceptibility and 3
Arm Caliper.
The key to interpreting multi-parameter borehole data is data integration. It is truly a
multivariate data set with varying correlations between physical parameters for different
lithological units. Spreadsheets and most graphical display packages are primarily 2dimensional, whereas geophysical borehole data, is 4-dimensional (x,y,z position and
physical parameter). To achieve easy access to data in a multi-well, multi-parameter
setting requires construction of a relational database. In this type of setting it becomes
relatively simple to test hypotheses on the basis of physical property, depth, location, or
any combination of parameters.
Physical properties can discriminate lithoclasses on the basis of discreet clusters of points
on 2D, or 3D cross plots. The degree to which the points cluster versus the separation
between individual cluster centroids defines the “uniqueness” of each lithoclass. 2D cross
plots from single holes allow the log analyst to verify that the geophysical (lithoclass)
1,3
71 Cranbrooke Ave., Toronto, Ontario, M5M1M3, Canada. Email: [email protected], [email protected]
1William Morgan Drive, Toronto, Ontario, M4H 1N6, Canada. Email: [email protected]
4
Applied Geophysics Research Group, School of Geography and Geology, McMaster University, Hamilton, Ontario
Email: [email protected]
2
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
boundaries are compatible with known geological lithological boundaries. Multi-well
cross plotting allows the analyst to determine if the same discriminant parameters are
applicable across the whole body. Having picked correlative discriminant lithoclasses the
analyst can then construct 3D models showing the geometry of lithoclass surfaces.
Within the Guacho Kuĕ property petrophysical analysis suggests three main lithoclasses
of kimberlite; K1, K2 and K3. Each lithoclass can be further subdivided into secondary
classes; K1a, K1b and K1c, K2a and K2b, K3a, K3b, K3d. The granite host rocks of the
Guacho Kuĕ property exhibited physical properties that are substantially dissimilar from
the kimberlites and can be subdivided into three distinct, granitic lithoclasses: G1, G2 and
G3. Multiwell cross plotting indicates that kimberlite bodies 5034 and Hearne appear to
have similar physical rock properties, based on the degree of clustering within each
defined lithoclass. Kimberlite bodies Tuzo and Tesla appear to have independent and
unrelated physical rock properties compared to 5034 and Hearne.
Krigging the individual parameters along selected sections allows the log analysts to
develop an initial conception of the geometry of the kimberlite phases within each
independent body. The process of multiwell analysis further allows the log analysist to
derive the conceptual geometric model based on the ability to identify the unique
interactions of measured parameters.
Introduction
Exploration of the grade potential of a mineral prospect has traditionally been established
by diamond or reverse circulation drilling of a series of holes. The geometry and grade of
the deposit was estimated by a combination of chemical assaying and land geological
mapping. These quantitative and qualitative techniques provide only limited information
from the borehole resolution of deposit grade, which depends on the interval sample.
Also, in lithologically complex terrain each geologist logging core may employ different
criteria for the discrimination of the lithoclasses. In recent years there have been many
advances in borehole geophysical tools. Physical rock property logging is the
measurement of the response of the earth, through which the drill hole passes, to various
electrical and radioactive pulses emitted from geophysical logging tools and the naturally
occurring emissions. Simultaneously there have been a dramatic change in the
sophistication of borehole interpretation software. Increased computing power of the PC
platform has facilitated increased use of graphical interpretation routines.
Geological Setting
The Slave Structural Province of the Northwest Territories, Canada, is an Archean
segment of the North American Craton. It composed of granites, gneisses and
supracrustal rocks (Pell, J.A, 1997) and is a classic setting for diamondiferous
kimberlites. The kimberlites of the Slave Province are not exposed at the surface and
have been found using a variety of techniques ranging from; heavy mineral sampling,
geophysical techniques and drilling. The typical geophysical signatures are high or low
magnetic anomalies and resistivity lows. The principle diamond bearing kimberlites are
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
found in the Lac de Gras region, in the east central slave Province. The kimberlites
intrude the granites and metasedimentary rocks as well as diabase dykes (Pell, J.A. 1997).
Typically they include crater and massive hypabyssal facies and some diatreme facies
may also be present (Pell, J.A. 1997).
Data Collection
703480
703500
7036000
Multiparameter borehole geophysical measurements were collected at the Guacho Kuĕ
property in the Lac de Gras area, Northwest Territories, to obtain in situ physical rock
property data in kimberlites and their host rocks. Four pipes on the property were probed
including; 5034, Hearne, Tuzo and Tesla. The tools used for this survey included; Natural
Gamma, Neutron-Neutron, Gamma-Gamma, Inductive Conductivity, Spontaneous
Potential, Point Resistance, Magnetic Susceptibility and 3 Arm Caliper. A total of 71
holes were surveys for the project including 28 NQ, diamond drilled holes and 43 reverse
circulation holes ranging in diameter from HQ to 12.75” (33.15cm). Below are the
individual body outlines and hole locations.
MPV-9946L
MPV-9916C
MPV-9940L
MPV-9944L
Northing
703480
7035950
MPV-9902C
MPV-9725C/24C
MPV-9919L
MPV-9918L
MPV-9948L
MPV-9913C
7035850
MPV-9911C/14C
588400
MPV-9950L
MPV-9904C
MPV-9910C
MPV-9937L
588300
MPV-9922L
MPV-9949L
MPV-9903C
7035750
588200
MPV-9920L
MPV-9913L
MPV-9921L
MPV-9939L
MPV-9947L
MPV-9912C
MPV-9916L
MPV-9915L
MPV-9941L
7035800
703460
703470
MPV-9945L
703450
Northing
MPV-9942L
588500
588600
588700
MPV-9713C/9726C
588800
589700
Easting
Figure I: Hearne Kimberlite Pipe
589750
589800
589850
Easting
589900
589950
Figure II: Tuzo Kimberlite
Pipe
Multiwell Analysis of Physical Properties
7035400
MPV-9909C
7035300
MPV-9951L
MPV-9905C
MPV-9933L
MPV-9954L
MPV-9929L
MPV-9936L
MPV-9952L
MPV-9931L
MPV-9953L
Northing
MPV-9928L
MPV-9903L
7035200
7036250
Northing
7036300
7035500
MacMahon, Wallace, Kassenaar and Morris
MPV-9901L
MPV-9914L
MPV-9904L
MPV-9902L
MPV-9907L
MPV-9905L
MPV-9909L
MPV-9908L
7035100
MPV-9906L
7036200
MPV-9912L
MPV-9911L
MPV-9910L
MPV-9907C
589100
Easting
MPV-9908C
589150
589200
589200
Figure III: Tesla Kimberlite Pipe
589300
589400
Easting
589500
589600
Figure IV: 5034 Kimberlite Pipe
he four kimberlite pipes which encompass the core of this study, were chosen based on
the variety of occurring kimberlitic facies both within the pipes and between the pipes.
The geophysical physical rock property signatures exhibited by each of the primary
facies; Hypabyssal kimberlite, Tuffisitic kimberlite and Volcaniclastic kimberlite can be
readily distinguished by distinct changes in either one or more of the parameters, using
crossplots and composite plots of the logs. Secondary features within these facies are
less unique and require a more rigorous approach, specifically some form of multivariate
analysis and classification routines. The host rock, in all cases is granitic in composition,
and exhibits distinct physical properties, allowing for straightforward interpretations.
Data Reduction
The preliminary step in any borehole physics project is to plot the raw traces of each
parameter per drill hole and apply the necessary hole corrections and normalizations.
Figure V, shows a typical corrected field plot, each trace is reserved for one parameter,
where each parameter highlighted by different colors. Geophysical picks are then made,
based on visual observations of how each parameter responds to a different lithology, i.e.
For example this kimberlite, granite shows a high neutron, high gamma, low density
response, where as kimberlite will have a low neutron, low gamma, higher density
response in most cases. This is called preliminary picking, whereby the log analysist
establishes the basic boundaries between two very distinct and unique litho units.
Secondary and tertiary picking (K1, K1a, K2, K2b), within the primary classifications,
can be highly subjective and very dependent on the ability of the log analyst to accurately
discriminate between slight changes in response per parameter AND the relationship of
that response to the other parameters. The objective, via visual discrimination, is to
establish UNIQUE lithoclasses as defined by all the parameters. This is usually done
without the aid of the geological interpretation, thus making the geophysical
interpretation unbiased.
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
DeBeers Canada
MPV-9905L
BOREHOLE GEOPHYSICAL PROFILES
237.1 m
7035165
N/A
-90°
589389
Feb 1999
12.25"
Feb 9, 1999
Woody Coulson and Jim Atkinson
5034 KIMBERLITE PIPE
KENNADY LAKE, NT
Depth Scale = 1:1250
Depth
Gamma Ray
(CPS) 350
(Metres) 0
0
400
Neutron
(CPS) 2000
Rel Density
2
2.9
Mag Sus
0 (Log SIx10-3) 1.5
5
Ind Cond
(mS/m) 150
0
Point Res
(ohms) 600
-10
-20
-30
Sonic Vel
2000 (m/s) 7000
Caliper 3A
300 (mm) 400
Overburden
Kimberlite
K1
-40
-50
-60
Kimberlite
K1
-70
-80
-90
-100
-110
-120
Kimberlite
K1b
-130
-140
-150
-160
-170
Kimberlite
K1
-180
-190
-200
-210
-220
Granite
-230
-240
Figure V:Corrected multi parameter downhole geophysical field plot
Interpreting Physical Rock Properties for Kimberlites
During the development of an interpretation methodology close consultations were made
with the geologist logging the core from the delineation holes. The geology was
compared to the physical rock property signatures and the observations below form the
basis for the interpretation methodology.
1. Natural Gamma Ray
In the igneous/metamorphic environment of the slave geological province, the natural
gamma is prone to large variations (50 - 350 CPS). These large variations are due to
the presence of potassium-feldspar in the granite.
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
2. Dual Neutron Porosity
The neutron-neutron tool reacts to hydrogen content of the rock. Water being the
main source of hydrogen, the tool is mainly affected by porosity. The granites are a
very tight formation and respond with high neutron counts. The kimberlites absorb
many more neutrons and therefore respond with a variety of levels of lower counts.
Pore water may be the primary source of hydrogen in the less dense kimberlite. The
very dense (2.8g/cc) hypabyssal kimberlite has been seen to have a significant
amount of hydrogen as well. However given the high density the hydrogen may be
bound in the crystal structure of a hydrous phase of mica, such as phlogopite.
3. Dual Gamma Density
The relative density data is computed from the Gamma-Gamma tool. The Counts Per
Second (CPS) is inversely proportional to the bulk density, a linear relationship has
been assumed. From a visual standpoint, the density tool was used extensively to
discriminate between the three types of kimberlite. The hypabyssal kimberlite (HK)
is generally more dense than granite. The tuffisitic kimberlite (TK) is much less
dense than granite and the transitional kimberlite has a density in between HK and
TK. The granite response in the density logs was variable especially in the zones near
the kimberlite contact.
4. Magnetic Susceptibility
The magnetic susceptibility was continuously, measured up the hole every 5cm and
the resulting profile is much more reliable than static hand held measurements. The
profiles in the granites are variable, units of both high and low magnetite content
were observed. The kimberlites behave in a more predictable fashion. On average
the hypabyssal kimberlite contains more magnetic minerals than the TK. There were
TKB (transition kimberlite with hydrothermal alteration) kimberlites observed which
were the exception to this rule, they were seen to have moderate magnetic
susceptibility with low density. The transitional kimberlite units were variable and
magnetic susceptibility was not reliable for its interpretation.
5. Inductive Conductivity
The inductive conductivity instrument was helpful in showing the small variations in
electrical conductivity in the TK type kimberlites where the magnetic susceptibility is
low. This parameter was observed to have a high correlation to the magnetic
susceptibility in areas of high magnetic susceptibility.
6. Point Resistance
The point resistance tool was very useful in distinguishing between the HK and TK
kimberlite. The HK kimberlite and granite have a high resistance. The TK and
transitional are more conductive in varying amounts.
7. Sonic Velocity
The sonic P-wave velocity measured highest velocities in the granites and the HK
kimberlite. The lowest velocities were seen in the TK kimberlite. The velocity log is
erratic in the granites and consistent in the kimberlite. The sonic velocity data
partially reflects the density information within the wall rock. Another immediate
benefit of the sonic tool is the information about alteration zones near the kimberlite
contact. Erratic calculated velocities in the altered zones are the result of fractures
that diffract the transmitted wave and produce unreliable velocities. The pattern of
noise is diagnostic of highly fractured rock.
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
8. 3-Arm Caliper
The 3-arm caliper log is good indication of competence in kimberlite. The borehole
will change shape at the granite/kimberlite contact and it will also show a larger
diameter in the TK kimberlite, which is generally a soft rock. The caliper was used to
map zones of less competent TK kimberlite in both the Hearne and Tesla Kimberlite.
Lithology Classification System for Kimberlites
From the initial composite log interpretations three distinct kimberlite types were
interpreted, as were four country rock types. Subsets of these types were also identified
for each kimberlite using statistical comparisons. A three-tier system of classification
was used to facilitate the modeling of the bodies in the future. A brief description of each
kimberlite type is summarized below.
General Geological distinctions for Guacho Kuĕ
1. K
The letter K is given to all lithologies that are interpreted to be kimberlite i.e.
hypabyssal, and transitional kimberlite.
2. G
The letter G is assigned to all lithologies that are interpreted to be country rock i.e.
Granite and gneiss host rock, granite xenoliths with in kimberlite and any other
xenoliths.
Primary Distinctions for Guacho Kuĕ
1. K1
This rock was typically found to be a hypabyssal kimberlite (HK). The K1 is as
dense or denser than the granite host rock and displays similar high resistance and
low conductance in the electrical logs. Natural gamma and neutron counts are much
lower than the granites. Typically the magnetic susceptibility is high compared to
other kimberlites. Sonic velocities are high in the K1 kimberlite.
2. K2
This kimberlite is a medium response kimberlite that usually describes a transitional
zone within the kimberlite. This lithology is described by values that fall either in the
K1 range or the K3 range but is not uniquely either.
3. K3
The K3 response was usually found to coincide with tuffisitic kimberlite (TK)
intersections in the drill hole. The signature has low density, low sonic velocity, low
magnetic susceptibility, and low resistivity.
4. G1
The G1 granite is dense competent granite. This rock contains potassium feldspar
crystals that raise the natural gamma count far above a kimberlite rock signature. The
neutron log is also important in interpreting the granite, the neutron counts are very
high in fresh granite due to the extreme low porosity.
5. G2
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
G2 is altered granite, which resides along fractures in the country rock. The granite
has had a large portion of the quartz crystals removed and this pore space is seen in
the neutron, density and sonic velocity data. The neutron CPS readings are near the
kimberlite range but the potassium feldspar is still present and gives Natural Gamma
CPS readings in the granite range.
6. G3
This is a subset of G1 that has the same properties as G1 except a low natural gamma
count, which probably reflects low potassium feldspar content.
7. G4
G4 is an unusual signature from a xenolith inclusion. For example a very low gamma
count with a high neutron might indicate a meta-sedimentary xenolith.
Secondary Distinctions for Guacho Kuĕ
1. K1a & b
The distinction between K1a and K1b is seen in the kimberlite/granite contact zones
or K1/K3 contacts zone. The K1b is the hard core of a K1 unit and the K1a zones
reside near the contact and shows signatures which begin to decline from the K1b
extremes.
2. K1c
The K1c lithology is very similar to the K1b in density, sonic velocity and point
resistance. The distinction is made in the neutron and magnetic susceptibility. This
dense, fast and resistive rock has high hydrogen content as indicated by the low
neutron readings. The magnetic susceptibility is also low in this rock which is
unusual for the K1 lithology.
3. K3a & b
The distinction between K3a and K3b is seen to be mostly a function of density, sonic
velocity and borehole rugosity. The K3a lithology is a relatively competent
kimberlite with typical low K3 signatures. K3b is an even lower density kimberlite
where the borehole walls are very weak and a slight rise in sonic velocity occurs in
most cases. This weakness result in extreme bore hole caving and the caliper log
maps these zones very accurately.
4. K3c
K3c signature is typically K3 except for an elevated Natural Gamma response. These
increases are most likely due to highly fractured granites in the kimberlite. There is
also a higher than normal magnetic susceptibility that might also be due to the
magnetite in the granite within the breccia.
Database Construction
Data storage is a fundamental aspect of any geophysical survey. Historically, data has
been stored in spreadsheets, bound by row-column layout, to either view or manipulate
the data. As mentioned previously, downhole geophysics is essentially a multivariate data
set. The interpretation, analysis and final model are part of an integrated solution that best
describes the problem and answers the relevant questions that arise through the
interpretation process. A portion of the data analysis methodology is one based on
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
visualization and descriptives, the underlying ability to search and manipulate the data
and separate it from storage is paramount. This can be achieved be setting up a relational
database.
A database is collection of records and files that are organized for a particular purpose.
The design and structure of the database arises from how the data will be defined (i.e. the
type of data and how the data is related), manipulated (i.e. filtering, relating, sorting) and
controlled (user access, read only, etc.). The functionality then rests on the ability to
relate the fact that each record in the database contains information related to a single
subject and only that subject. In a relational database all the data is stored in tables. The
tables store information about the subject and have columns that contain different kinds
of information about the subject and the rows that describe all the attributes of a single
instance of that subject. A query, run on one or more tables results in something that
resembles another table, but only the query is stored not the resulting table. The choice of
database software rests solely on the user, this project utilized Microsoft Access.
VIEWLOG is programmed to readily upload LAS files and/or VIEWLOG *.hdr files
created in the field, in a fast and efficient manner. Template header files that are created
in VIEWLOG and dynamically linked to the database allow for easy and friendly user
access.
Composite plots for each hole, can then be created, integrating both the interpreted core
or chip geology with the geophysical parameters and interpretation. The results are
shown in figure XI. Composite plots are essentially the final trace plot created. The
information is presented in a format that is visually intuitive, where colors allow the
untrained eye to key in on the important geophysical boundaries.
DE BEERS CANADA EXPLORATION INC.
BOREHOLE GEOPHYSICAL PROFILES
HEARNE Kimberlite Pipe
Large Diameter Drill Hole
MPV-9945L
Northing: 7034720
Easting: 588455
Drilled:
Logged: 3/11/1999
Surveyed by: QLS
Project Number: 4058
Length: 155
Azimuth:
Dip: -90
Diameter: 12.25"
Processed by:
Comments:
Petrology
Depth
(Metres)
0
Gamma Ray
(CPS)
350
400
Neutron
(CPS) 2000
Rel Density
2
2.9
Mag Sus
.01 (Log SIx10-3) 50
5
Ind Cond
(mS/m)
150
0
0
0
Point Res
(ohms) 500
SP
(MV)
500
2000
Sonic Vel
(m/s) 7000
300
Caliper 3A
(mm)
400
Geophysical Intrep
ICE/WATER
ICE/WATER
OVB
OVB
-20
HK
K2
-30
HK
-40
HK
K3b
G2
K3a
K2
-50
HK
-10
K3a
K2
-60
-70
K1a
-80
HK
-90
K1b
-100
K1a
-110
K1b
-120
GRAN
G1
-130
K2
-140
HK
-150
K1b
Figure VI: Composite plot for MPV-9945L from Hearne Kimberlite Pipe
Cross plots
There is an iterative process between creating the final composite plots and single well
cross plots. Cross plots of two or more parameters, keyed to the geophysical lithoclasses
give a visual check on the original geophysical boundary picks. The definition of a
lithoclass is a UNIQUE grouping of measurements, as defined by a set of given
geophysical parameters. The degree to which the class is unique, within the constrains of
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
EDA methodology, is established via visual discrimination from field plots and cross
referenced by cross plots.
On a cross plot, a lithoclass is represented by a cluster of points. The degree to which the
points cluster in conjunction with the extent of separation between the individual clusters
defines the “uniqueness” of each lithoclass. In VIEWLOG there are a number of ways of
presenting the data; from 2D plots and 3D plots of individual holes to multiwell cross
plotting in both dimensions. 2D cross plots from single holes allow the log analysist to
visually verify the geophysical picks and make the corresponding adjustments. Multiwell
cross plotting allows for the integrated solution, by plotting a series of holes together,
testing the association, relationship and more importantly the correlatibility of the
lithoclasses across the body.
Cross plots also provide a visual cross-referencing methodology on the calibration and
normalization procedures. Though many of the calibrations, for individual parameters are
derived from predetermined processes, in many cases serious errors can result. Cross
plots in combination with composite plots provide a method of quality assurance and
quality control, before the logging has been completed.
Discussion
The first challenge is to visually, recognize which parameter(s) or factor(s) are the most
important to discriminate the independent lithoclasses. The second is to establish whether
or not there are relationships/correlations between the kimberlite bodies. In the subsections below are a series of cross plots from the four kimberlite bodies.
5034
Examination of several combinations of physical property measurements from the 5034
kimberlite pipe, established that the factors of primary importance included, neutron
(cps), density (g/cc)), natural gamma (cps) and sonic velocity(m/s). Figure VII, shows
how the granite classes can be classified on the bases of only two physical properties. The
degree to which they are unique will be further quantified by classical statistical
techniques. Of significance is the lack of clustering within the granite lithoclass.
However; Figure VIII, shows that the combination of sonic velocity and density control
the degree of clustering. Figure IX, a 3D cross plot, displaying Sonic Velocity, Density
and Neutron, shows the importance in understanding the effect that a combination of
parameters has on the ability to define each lithoclass.
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
Multi W ell Physical Rock Properties Cross Sections
Multi W ell Physical Rock Properties Cross Sections
5034 Kimberlite Pipe
4
5034 Kimberlite Pipe
Natural Gamma (cps)
100
200
Intervals:
ICE/WATE
K1a
K1b
K1c
OVB
K3a
K3b
K2
G2
G1
G3
K3
3.5
300
Intervals:
ICE/WATE
K1a
K1b
K1c
OVB
K3a
K3b
K2
G2
G1
G3
K3
Boreholes:
2.5
MPV-9901L
MPV-9902L
MPV-9903L
MPV-9904L
MPV-9905L
MPV-9906L
MPV-9907L
MPV-9908L
MPV-9909L
MPV-9910L
MPV-9911L
MPV-9912L
MPV-9914L
2
0
MPV-9901L
MPV-9902L
MPV-9903L
MPV-9904L
MPV-9905L
MPV-9906L
MPV-9907L
MPV-9908L
MPV-9909L
MPV-9910L
MPV-9911L
MPV-9912L
MPV-9914L
Density (g/cc)
3
Boreholes:
600
800
1000
Neutron (cps)
1200
1400
Figure VII: 2D Multiwell Cross Plot of
5034, Neutron (cps) vs. Natural
Gamma (cps)
ICE/WATER
K1a
K1b
K1c
OVB
K3a
K3b
K2
G2
G1
G3
2000
3000
4000
5000
Sonic Velocity (m/s)
6000
7000
8000
Figure VIII: 2D Multiwell Cross Plot
of 5034, Sonic Velocity(m/s) vs
Density (g/cc)
Multi Well Physical Rock Properties Cross Sections
5034 Kimberlite Pipe
Figure IX:3D Multiwell Cross Plot of 5034, Sonic Velocity (m/s) vs. Density
(g/cc) and Neutron (cps)
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
Hearne
Multi W ell Physical Rock Property Cross Plots
Hearne Kimberlite Pipe
Multi Well Physical Rock Property Cross Plots
Sonic Velocity (m/s)
4000
5000
Boreholes:
1400
Boreholes:
MPV-9937L
MPV-9939L
MPV-9940L
MPV-9941L
MPV-9942L
MPV-9944L
MPV-9945L
MPV-9946L
MPV-9947L
2000
600
3000
MPV-9937L
MPV-9939L
MPV-9940L
MPV-9941L
MPV-9942L
MPV-9944L
MPV-9945L
MPV-9946L
MPV-9947L
Intervals:
K1a
K1b
OVB
K3a
K3b
K3c
K2
G2
G1
G4
K1
K3
1200
6000
7000
Intervals:
K1a
K1b
OVB
K3a
K3b
K3c
K2
G2
G1
G4
K1
K3
Neutron (cps)
800
1000
8000
Hearne Kimberlite Pipe
0
100
200
Natural Gamma (cps)
300
2000
Figure X: 2D Multiwell Cross Plot of
Hearne, Sonic Velocity (m/s)) vs.
Natural Gamma (cps)
3000
4000
5000
Sonic Velocity (m/s)
6000
7000
8000
Figure XI: 2D Multiwell Cross Plot of
Hearne, Neutron (cps) vs. Sonic
Velocity (m/s)
The physical properties of the Hearne kimberlite pipe can be, from a visual aspect, much
better constrained than 5034. The two classes of kimberlite K1, K2 and K3 show a good
degree of clustering and “uniqueness”. As with 5034 the granite lithoclasses and
distinguishable from the kimberlites, but have a lesser tendency to cluster. Examining the
relationships between the physical properties we can make the preliminary assumption
that neutron exhibits the best ability to cluster the lithoclasses, whereas the remaining
properties show the degree of separation. This is best shown by the 3D cross plot in
Figure XII.
K1a
K1b
OVB
K3a
K3b
K3c
K2
G2
G1
G4
K1
K3
Multi Well Physical Rock Property Cross Plots
Hearne Kimberlite Pipe
Figure XII: 3D Multiwell Cross Plot of 5034, Sonic Velocity (m/s) vs. Density (g/cc) and
Neutron (cps)
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
Tesla and Tuzo
Preliminary observations of Tesla and Tuzo indicate that they have a substantially
different physical rock property response than either 5034 or Hearne. Although the
physical properties from both Tesla and Tuzo appear different, the signatures reflect the
alteration/dilution of the K3 kimberlite. The various forms of K3 (i.e K3b, K3c and K3d)
are only found in these two kimberlites, therefore a relationship between the four
kimberlites can not be readily established. Although Tesla and Tuzo have some
occurrences of K1 and K2, it is difficult from this kind of graphical representation to
clearly establish a regional relationship between the bodies.
Multiwell Physical Rock Properties
Multi W ell Physical Rock Property Cross Plots
Tesla Kimberlite Pipe
300
Tuzo Kimberlite Pipe
1400
Intervals:
K3 Semi D
K3b Dilute
K3 Diluted
ICE/WATE
OVB
G1
G4
K1
K3
1200
200
250
Intervals:
K3b Dilute
ICE/WATE
OVB
K3a
K3b
K2
G1
K1
K3
Boreholes:
Boreholes:
Neutron (cps)
800
1000
MPV-9913L
MPV-9916L
MPV-9918L
MPV-9919L
MPV-9920L
MPV-9921L
MPV-9922L
MPV-9948L
MPV-9949L
MPV-9950L
0
600
50
Natural Gamma (cps)
100
150
MPV-9928L
MPV-9929L
MPV-9931L
MPV-9933L
MPV-9936L
MPV-9951L
MPV-9952L
MPV-9953L
MPV-9954L
2000
3000
4000
5000
Sonic Velocity (m/s)
6000
7000
8000
Figure XIII: 2D Multiwell Cross Plot
of Tesla, Natural Gamma (cps) vs.
Sonic Velocity (m/s)
1
1.5
2
2.5
Density (g/cc)
3
3.5
4
Figure XIV: 2D Multiwell Cross Plot
of Tuzo, Neutron (cps) vs. Density
(cps)
Cross Sections and 3D models
Multiwell cross plotting allows the log analyst to visualize and discriminate between the
individual litho class occurrences downhole with no emphasis on the geometry of the
body or the distribution of the classes. Geological models can be constructed from a
number of interpreted boreholes across a section. Intial unbiased estimates of the
geometry of the lithological boundaries can be obtained by Krigging individual physical
property parameters. The resulting grids estimates the position of the lithological
contacts. Incorporating this with the interpreted lithological units gives a geological
section or 3D model.s
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
Multiwell Physical Rock Properties
Tesla Kimberlite Pipe
K3b Diluted Zone
ICE/WATER
OVB
K3a
K3b
K2
G1
K1
K3
MPV-9947L
I
G
I
G
MPV-9939L
MPV-9945L
MPV-9941L
I
G
I
G
MPV-9942L
MPV-9944L
I
G
MPV-9940L
I
G
I
G
El evat ion
-100
0
I
G
MPV-9946L
Figure XV: 3D Multiwell Cross Plot of Tesla, Natural Gamma (cps) vs. Sonic
Velocity (m/s) and Neutron (cps)
MPV-Hearne
-200
Point Resistance (Ohms)
Spontaneous Potential
0
250
500
750
1000
1 250
13 00
Vertical Exageration: .5
- 300
Section Offset DIstance: 25
Ho rizontal Scale
0
50
100
S ec ti o n D i s tanc e
1 50
20 0
0
40
metres
80
Figure XVI: Point Resistance (Ohms) Grid of Hearne Cross Section
MPV-9947L
MPV-9939L
I
G
I
G
I
G
I
G
MPV-9945L
MPV-9941L
MPV-9942L
I
G
MPV-9944L
MPV-9940L
I
G
I
G
MacMahon, Wallace, Kassenaar and Morris
El evat ion
-1 00
0
I
G
MPV-9946L
Multiwell Analysis of Physical Properties
MPV-Hearne
- 200
Sonic Velocity (m/s)
Sonic Velocity
2 500
3 000
4000
5 000
6 000
600 0
Vertical Exa geration: .5
- 300
Section Offset DIstance: 25
Horizontal Sca le
0
50
10 0
S ec ti on D i s tan c e
15 0
20 0
0
40
metres
80
Figure XVII: Sonic Velocity (m/s) of Hearne Cross Section
Hearne Kimberlite Pipe North/South Cross Section
I
G
MPV -9937L
MPV -9947L
G I
I
G
MPV- 9939L
MPV-9945L
MPV -9941L
I
G
I
G
MPV -9942L
MPV -9944L
I
G
I
G
I
G
MPV -9940L
MP V-9946L
-300
-200
Elevation
-100
G I
0
100
Geophysical Intrepretation Derived From Multiparameter
Physical Rock Properties
0
100
200
300
400
Section Distance
Figure XVIII: Geological Interpretation Derived from Multiparameter physical Rock
Properties for Hearne Cross Section
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
Figure XIX: 3D Geological Interpretation Derived from Multiparameter physical Rock
Properties for Tuzo.
Conclusions
As an initial step into understanding the large volumes of data that are typically generated
by downhole geophysics, the value of visual exploration cannot be underestimated. The
process of defining the litho classes based on physical properties allows for detailed,
probabilistic insight from which a preliminary model can be generated.
Treating each pipe as a unique occurrence a number of observations can be established
based on the geophysical interpretation;
a) Granite possess physical properties that are substantially dissimilar from the
kimberlites of which there are three lithoclasses: G1, G2 and G3.
b) There are three main lithoclasses of kimberlite; K1, K2 and K3. A general observation
concludes that:
K1 = HK (Hypabyssal kimberlite)
K2 = HK (Hypabyssal kimberlite)
K3 = MK and VK (Magmatic kimberlite and Volcaniclastic kimberlite)
Note: MK ( Magmatic kimberlite is a term currently out of favor and was employed at the
time to describe a transitional facies between TK (Tuffisitic kimberlite) and VK
(Volacniclastic kimberlite)
c) Each lithoclass can be further subdivided into secondary classes;
K1 = K1a, K1b and K1c
K2 = K2a and K2b
K3 = K3a, K3b, K3d and various diluted and semi diluted zones which are
particular to the Tesla body.
d) Kimberlite bodies 5034 and Hearne appear to have similar physical properties.
e) Kimberlite bodies Tuzo and Tesla appear to contain only a selection of the same
lithoclasses that were identified in 5034 and Hearne. The implication is that Tuzo and
Multiwell Analysis of Physical Properties
MacMahon, Wallace, Kassenaar and Morris
Tesla either represent a different stratigraphic level in the kimberlite pipe or are a altered
(hydrothermal) version of the defined lithoclasses.
f) Identification of lithoclasses on the basis of clusters in association with log plots
permits a more exact definition of the depth of lithoclass boundaries.
g) Adoption of a single log classification scheme is valuable in the construction of 2D
and 3D geological cross sections, which in turn provide important economic
ramifications.
Pell, P.A., Kimberlites in the Salve Craton, Northwest Territories, Canada. Geoscience
Canada, Volume 24, Number 2 pg. 81-89.