Tight Rock Analysis Tests product sheet

TerraTek TRA Tight Rock Analysis Service—
Integrated Workflow
For successful tight gas and oily shale analysis
Task 1: Pre-evaluation of log data
TerraTek HRA* heterogeneous rock
analysis service
APPLICATIONS
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Gas-in-place resource evaluation (free
and adsorbed) in cored well
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Determination of containment
of hydraulic fracture stimulation
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Maximization of retained-fracture
conductivity
Task 2: Petrophysical property identification
TerraTek TRA service
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Propagation of core-measured field
properties using logs
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Maximized recovery through
Tailored version of hydraulic fracture
design, including proper selection
of fracture proppant and fluids
●● Assessment of horizontal stress
for fracture containment
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Task 6: Petrographic description
XRD
Integration of all data with well logs
Capability to resolve
nanodarcy permeabilities
Measurements of fluid saturations,
effective porosities, and matrix
permeabilities in tight reservoirs
Isotherm measurements and canister
desorption and adsorption
Anisotropic mechanical properties
Detailed petrology and X-ray
diffraction (XRD) analysis
Fluid sensitivity evaluation
Log-based modeling of all above
properties, including petrology
Continuous strength profiling
(scratch testing)
Task 5: Core fracture analysis
FEATURES
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Adsorption isotherm analysis
Task 4: Core description and continuous
strength profiling
■■ Detailed ithologic core description
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Total organic content (TOC)
Task 3: Gas-in-place estimation
Canister desorption and gas-species analysis
Well-specific completion strategies in
highly variable, heterogeneous systems
BENEFITS
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Continuous core spectral
gamma ray measurements
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Stress frames are used to conduct tests on cylindrical
samples with diameters ranging from 0.5 to 6 in. Tests
include uniaxial strain; triaxial, multistage triaxial, and
unconfined compressions; and controlled stress path,
thick-walled cylinder, and tensile strength. Application of
extreme pressure is also available with up to a 60,000-psi
confining pressure, a 30,000-psi pore pressure, and a
>500,000-psi axial stress (1.5-in diameter sample).
The fully integrated TerraTek TRA* tight rock
analysis service characterizes heterogeneity,
reservoir quality, and completion quality in
unconventional reservoirs.
The workflow includes tasks that are
outlined on the right, then detailed on the
following pages.
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Thin-section microscopy
Scanning electron microscopy of
traditional and ion-milled samples
Task 7: Mechanical property determination
Multistress compression test
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Task 8: Rock-fluid system service
Proppant embedment
and fracture conductivity
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Permeability reduction
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Fluid compatibility
Task 9: Analysis and modeling
Reservoir quality log
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Completion quality log
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Solids production modeling
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Wellbore stability modeling
TerraTek TRA Tight Rock Analysis Service—Integrated Workflow
Task 1: Pre-evaluation of log data for core interval selection
TerraTek HRAservice evaluates the variability of all log measurements
as a function of depth, create a pattern of these combined responses,
and identify the occurrence of identical data patterns along the length of
the well (or the interval of interest using pattern recognition technology).
Results from the analysis identify all existing, nonredundant lithologies
(rock classes) with distinct material properties along the region of interest.
When performed on nearby offset wells, TerraTek HRA service can
be used to identify the distribution of rock units and determine the
optimal coring location to represent the most variability. When sidewall
cores are taken, log measurements on the same well or from adjacent
wells are used to define the depth ranges and minimum sampling
requirements to obtain adequate representation. For laboratory sample
selection from cores, TerraTek HRA service is used to define the optimal
number of samples required for adequate characterization of each rock
class (reservoir and seals).
Task 2: Petrophysical property identification
Petrophysical measurements are conducted using TerraTek TRA
service to determine reservoir parameters of porosity, permeability,
and fluid saturation. These measurements are fundamental for gasin-place and gas productivity evaluations. TerraTek TRA service uses
leading techniques for accurately measuring petrophysical properties
of tight gas and oily shales and sandstones. TerraTek TRA service is
employed to characterize the gas-filled and effective porosities, the fluid
saturations, including mobile hydrocarbons (such as condensates), the
as-received matrix permeability to gas, and TOC. Twelve petrophysical
parameters are measured and reported.
The combined evaluation of heterogeneous rocks, gas-in-place, geochemistry, petrology, and petrophysical results provides a complete
definition of the optimal reservoir units in the section logged and defines
the adsorbed and interstitial gas in place.
Task 3: Gas-in-place estimation
Meaningful estimates of gas-in-place reserves—and subsequent
deliverability of this gas—require accurate formation evaluation. The
data are obtained by measuring the volume and rate of gas released
from recovered core at the wellsite (canister desorption). They are also
acquired through laboratory adsorption isotherm and gas-filled porosity
and permeability measurements. Lost gas analysis is then conducted to
estimate gas in place. Gas analysis and geochemical characterization
provide fundamental complementary information for gas composition,
organic content, kerogen type, and kerogen maturity. The following
tests are specifically recommended:
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canister desorption analysis
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adsorption isotherms
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desorbed gas analysis
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vitrinite reflectance
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elemental logging
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TOC
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rock evaluation pyrolysis
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free gas porosity.
Task 4: Core (geological) description and continuous
strength profiling
Detailed geological description of the slabbed core is essential
for defining lithological units and, in combination with petrological
analysis, provides the fundamental mineralogical, textural, or diagenetic
factors defining the multiple reservoir units and seals. In shales, seemingly
subtle variations in mineralogical character, cementation, or depositional environment may result in drastic changes in gas productivity or
in mechanical boundaries. These subtle differences may in turn control
fracture spacing, distribution, orientation, and conductivity.
The continuous profiling core scratch test system used in TerraTek
service provides a continuous unconfined compressive strength (UCS)
measurement that is used to map rock heterogeneity and provide a
quantitative means of locating intervals requiring further evaluation.
The system has become critical in correctly defining facies and heterogeneities difficult or impossible to observe by geological description or
Net Effective Stress (psi)
1E+07
0
1000
2000
3000
4000
5000
6000
7000
Permeability (nD)
1E+06
1E+05
Pressure Decay Permeability
1E+04
Pulse Decay Plug Permeability
1E+03
1E+02
TerraTek TRA service includes using a pressure-decay permeability measurement system (left) capable of measuring matrix permeability in the nano-Darcy scale in microporous materials. Apparent stress-sensitivity measured via pulse-decay on whole plugs (bottom right) due to stress release microfractures (top right). TerraTek TRA service
eliminates these artifacts, allowing for more accurate determination of petrophysical properties.
TerraTek TRA Tight Rock Analysis Service—Integrated Workflow
log characteristics alone. Digital photography allows visual integration
of textural heterogeneity and the resulting strength heterogeneity.
Core fracture analysis includes the evaluation of natural and induced
fracture systems, fracture orientation, and mineral composition
of fracture fill. Typical tabulated data from the fracture analysis
include general fracture type, fracture dip orientation, type of
mineral fill, type of oil stain, apparent fracture dip, fracture porosity,
fracture spacing, and fracture intensity.
19,000
6
15,200
4.8
11,400
3.6
7,600
2.4
3,800
Task 6: Petrographic description
Scanning electron microscope (SEM) analysis, thin-section analysis,
and XRD analysis are fundamental to petrological description. Thinsection analyses are used for petrological description of the lithofacies
to establish a baseline correlation between the petrophysical and
geological and petrological descriptions. They are used as a screening tool for important reservoir parameter investigations such as
diagenetic alteration, cementation, and fracture fills.
SEM imaging involves high-magnification imaging of small, representative
reservoir samples and is required to identify clay morphology, kerogen
location, and pore characterization. Semiquantitative XRD analysis is
used to define clay composition and clay expandability and to build log
correlations. Certain shale lithofacies can be verified only by XRD analysis.
Petrological description from TerraTek TRA service provides textural and
mineralogical definitions to the unique log responses identified by the
TerraTek HRA service.
Task 7: Mechanical property determination
To increase recovery of reserves and develop completion strategies,
rock mechanics tests are required to assess the variability of elastic
properties and in situ stresses. In general, tight gas and oily reservoirs
are strongly heterogeneous and anisotropic. As a result, elastic properties are different in the vertical and horizontal directions. This contrast
in elastic properties is not directly measured by conventional seismic
logs and can have a dominant impact on hydraulic fracturing design and
predictions of in situ stress. Therefore, to maximize the effectiveness of
completion strategies, the evaluation of anisotropic material properties
and the in situ stress throughout the well (e.g., in situ stress variations
with respect to reservoir units and seals) are of critical importance.
Fracture toughness and tensile strength are also fundamental parameters
required for hydraulic fracturing design and modeling. Measurements of
anisotropic material properties, fracture toughness, and tensile strength
are conducted on all reservoir units and seals to evaluate the contrast
of these properties between lithological units, and thus to evaluate their
effect on fracture propagation and containment.
Measurement of the mechanical properties of tight shales requires
reservoir effective stress conditions to be applied to the samples. Thus,
pore pressure and Biot’s coefficient, which may be much less than unity
0
–0.5
P wave
S wave
Axial strain
0
0.5
1
1.5
2
2.5
Axial stress difference, ×1E4 psi
Axial strain, %
Task 5: Core fracture analysis
Ultrasonic velocity, ft/s
TerraTek HRA service and continuous strength measurements along
the core are used to determine optimal sample locations for laboratory
testing and gain a better understanding of sample-core and core-log
scaling relationships.
Triaxial compression depth: 7,453.05 ft
1.2
3
0
3.5
Axial stress is measured versus strain during triaxial compression testing.
Ultrasonic velocity measurements of P and S waves are captured during loading
up to the point of failure. Measurements allow the characterization of static and
dynamic elastic properties and the stress dependence of dynamic properties.
in a tight shale, are needed. Biot’s coefficient in tight gas and oily shales,
short and long-term creep effects, rock hardness, proppant embedment
potential, and proppant fluid sensitivity can all be measured.
Task 8: Rock-fluid system service
Understanding the rock-fluid system (RFS) in unconventional reservoirs
is critical for completion optimization. The RFS includes the rock, saturating fluids (both hydrocarbons and connate water), soluble minerals,
and introduced completion fluids. Fluid flow behavior and rock type are
tightly coupled in these reservoirs due to the high surface areas, the
very high capillary pressures, and the complexity of both organic and
mineral surfaces that exist in these complex pore structures. The RFS
package offers multiple services to characterize rock–fluid interactions.
Surface area and pore characterization
Gas sorption, mercury-injection capillary pressure (MICP), and cationexchange capacity (CEC) measurements are used to characterize the
surface area and pore structures of the rock.
Native fluids extraction and characterization
Services are offered to extract and characterize the native hydrocarbons in unconventional rocks. Characterization of composition
and phase behavior at reservoir temperatures and pressures can
be done in conjunction with Schlumberger Reservoir Laboratories.
Connate water characterization scaling potential, salt migration,
and mineral dissolution
Unconventional reservoirs often contain vast quantities of salt and readily
soluble minerals that can dissolve and diffuse into the introduced
fracturing fluids. Their variety of salts and minerals can be fully characterized, and full flowback fluid analysis is available from the Schlumberger
water analysis laboratory.
TerraTek TRA Tight Rock Analysis Service—Integrated Workflow
Texture, distribution, and condition of organic components is revealed
by SEM imaging.
Thin-section analysis, in combination with XRD data, is used to obtain matrix
composition (<4 microns), microtexture, amounts and compositions of silt and
microfossils, and diagenetic textures. Here, fossil composition is determined
by colored stains.
Chemomechanical effects
Numerous chemomechanical tests are routinely performed to measure
The RFS service package focuses on quantitative testing methods to
generate data that can be incorporated in reservoir simulation models.
All tests can be integrated into comprehensive custom service packages
along with geomechanical, petrological, core analysis, and HRA services
to provide a complete and detailed understanding of the rock-fluid
system in these reservoirs.
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loss of fracture conductivity due to proppant embedment
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loss of unconfined compressive strength (UCS) due to fluids exposure
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sensitivity of swelling clays
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rock failure and fines generation.
Testing can be performed with a variety of completion fluids and at
reservoir temperatures and pressures. Flowback pressure management
testing and modeling services are also provided.
Fluids retention and migration
The vast majority of the fluid pumped during fracturing treatments
stays in the formation. Where does it go? What does it do?
Services include
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quantitative imbibition
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quantitative fluid leakoff
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advancing and receding contact angles used to predict fluid imbibition
into the rock and the retention of fluid in the fracture.
Task 9: Analysis, modeling, and predictions of properties
with logs
Pre-evaluation of log data using TerraTek HRA service provides a mathematically precise, subjectivity-free, and robust methodology.
The process defines rock classes with distinct material properties and
propagates in situ stress profiles for fracture design. Tight rock and
core analysis and laboratory testing provide the fundamental petrologic,
physical, and mechanical properties for a comprehensive characterization of each of these rock units. Well-defined rock units and their wellcharacterized properties and log responses are used to develop a model
that predicts log responses alone. A direct result of this analysis is the
ability to predict all measured laboratory properties in subsequent wells
based on log measurements alone. Additional analysis of selected
properties provides continuous estimates of reservoir quality (e.g., gas
productivity potential) and hydraulic fracture containment across the field.
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