anisotropy of shale properties - ntnu
TRANSCRIPT
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106100 104 108 1012 1016 1018 1020
Frequency ( Hz)
Wavelength
Observation Scale
Anisotropy of Shale Properties:A Multi-Scale and Multi-Physics Characterization
Elastic, Mechanical, Petrophysical and Micro-Structural Properties at in situ conditions
Joel Sarout
Lionel Esteban, Claudio Delle Piane, Bruce Maney, D ave Dewhurst and Ben Clennell
CSIRO Earth Science and Resource EngineeringShale Research Consortium
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Motivation:Anisotropy of Fluid Transport
A
B
• A. Side-Burden: Permeability k along shale bedding• B. Over-Burden: Permeability k perpendicular to shale bedding
⇒ Calculate k for any angle (k second-rank tensor + shale T.I.)
Faulted reservoir Anticline reservoir
Need to assess:• Permeability anisotropy
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Affects seismic data processing, inversion and interpretation (cross-well, VSP, AVO, time-lapse, ray tracing, tomography…)
Source: NORSAR
Vertical Transverse Isotropy
Isotropy Tilted Transverse Isotropy
Motivation:Seismic/Ultrasonic Anisotropy
Source: Moore et al. (2007)
Nankai accretionary wedge offshore Japan’s southeas t margin
Need to assess:• Elastic anisotropy• Stress-dependence• Emphasis on Thomsen’s δ
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Need for Laboratory Characterizationof Rock Anisotropy for Field Applications
PhysicalProperties
CharacterizationScales
LaboratoryProbing Techniques
▪ Micro-Structure- 2-D (SEM)- 3-D (X-Ray CT)
▪ Water Content / Distribution▪ Fluid Transport
- Permeability- Diffusivity
▪ Mechanical Strength- Cohesion- Internal Friction Angle
▪ Elasticity-Static-Dynamic
▪ SEM 2-D Imaging
▪ X-Ray 3-D Tomography
▪ Water Circulation
▪ Nuclear Magnetic Resonance
▪ Triaxial Deformation
▪ Stress Anisotropy
▪ Scratching
▪ Wave Propagation
nm – 10-9m
����m – 10-
6m
mm – 10-
3m
cm – 10-2m↓ ↓ ↓ ↓ ↓ ↓ ↓km - 103m
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Anisotropy & Heterogeneity:
Scale-Dependent Concepts…?
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Evidence of Structural Anisotropy:High-Resolution Characterization (µm scale)
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Evidence of Structural Anisotropy:High-Resolution Characterization (µm scale)
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Low-Resolution Structural Characterization(mm to cm scale)
A-A B-B
80 m
m
Medical CT Scanner: Sample heterogeneity at mm scale
3D - High CT Contrast
3D - Low CT Contrast
80 m
m
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Anisotropyof
Fluid Transport
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Anisotropy of Water Permeability (cm)
Pressure Cell
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Testing Protocol:Constant Pressure Drop Method
PROTOCOL:1. Saturate: Pc = 20MPa – Pp = 10MPa2. Impose: PpU = 15MPa – PpD = 10MPa3. Monitor Injection Rate: Q
Permeability in flow direction (cm scale)
Q
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NMR Method: Field Gradient Method
Magnetic field gradient along Y-axis
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Perpendicular to BeddingS
cale
d A
mpl
itude
of N
MR
Sig
nal
T2 Relaxation Time [ µµµµs]
102103 104 105 106
Scaled Gradient Intensity
0
500
1000
1500
2000
3000
4000
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Parallel to Bedding 1S
cale
d A
mpl
itude
of N
MR
Sig
nal
T2 Relaxation Time [ µµµµs]
102103 104 105 106
Scaled Gradient Intensity
0
500
1000
1500
2000
3000
4000
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Parallel to Bedding 2S
cale
d A
mpl
itude
of N
MR
Sig
nal
T2 Relaxation Time [ µµµµs]
102103 104 105 106
Scaled Gradient Intensity
0
500
1000
1500
2000
3000
4000
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Peak NMR AmplitudesS
cale
d A
mpl
itude
of N
MR
Sig
nal
T2 Relaxation Time [ µµµµs]
102103 104 105 106
Scaled Gradient Intensity
0
500
1000
1500
2000
3000
4000
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Anisotropy of Water Diffusivity (nm to µm)
16
Squared Gradient Intensity (x10 6)
12840
Dh // / Dh ⊥⊥⊥⊥
Fast Diffusivity(Free water ) 1.5
Slow Diffusivity(Clay-Bound Water ) ~ 1
Pea
k A
mpl
itude
of N
MR
Sig
nal
160
115
Slow Diffusion
Fast Diffusion
Fit Double Exponential Function to NMR Signal Peaks
Water diffusivity proportional to slope of the tangent
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Permeability and Diffusivity Anisotropies over Different Scales
Parameter // / ���� Scale Effective Pressure
Permeability k 9.1 cm 7.5
Diffusivity Dh 1.5 nm-µm 0 S
kDh =
Pressure vessel withinmagnetic field currently tested
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Anisotropyof
Seismic Properties
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Specimen Instrumentation:Strain and P-wave (Group/Ray) Velocities
Viton Sleeve
∅∅∅∅transducers = 5 mm
fcentral ~ 0.5 MHz
80 m
m
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Over-Consolidated Triaxial Loading
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Seismic Data Processing
25 different Azimuth angles
17 different Dip angles
� ~ 90 different ray paths
Assumption:
Bedding/T.I. symmetry plane is horizontal
( ) ( ) ( ) ( )( )
( )°==
++≅
90
Angle Dip
coscossin1 422
P
P
V
V
αθ
θεθθδαθFit Thomsen’s weak anisotropy model to VP(dip)
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Group Velocities Function of Dip Angle:A Snapshot…
Average of n experimental points with identical dip angle
Fitted Thomsen’s model
95% Confidence interval
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Effect of Water Saturation
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Effect of Isotropic Stress
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Anisotropyof
Mechanical Properties
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Mechanical Anisotropy
No apparent difference between axial and radial strains
Differentiation between axial and radial strains
M// / M�= 0.54
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Effect ofStress Anisotropy
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Effect of Stress Anisotropy
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Effect of Stress Anisotropy (Triaxial):Low-Resolution Characterization (mm to cm scale)
A-A B-B
Axial Loading
A-A B-B
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(Preliminary) Conclusion
• Fluid transport anisotropy → strongly scale-dependent• Seismic anisotropy → strongly stress-sensitive• Mechanical anisotropy → poorly related to seismic anisotropy• Stress anisotropy → crucial factor controlling rock anisotropy…
• Anisotropy is a scale-dependent (theoretical) concept……not to be confused with the heterogeneity (practical) concept
• Anisotropy is also a property-dependent concept
⇒ Need to state scale and property when reporting anisotropy⇒ Given rock (nano-/micro-/meso-/macro-) structure gives rise to
different anisotropy magnitudes for various physical properties
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Questions…?
Acknowledgement of support from:
• BG Group• Chevron• ConocoPhillips• ExxonMobil
• Sinopec• Statoil• Total
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Effect of Stress Anisotropy (Triaxial):Low-Resolution Characterization (mm to cm scale)
A-A B-B
Shear Failure
Tensile Failure
Stress Unloading
Axial Loading