Anisotropy of Shale Properties: A Multi-Scale and Multi-Physics Characterization

Transcription

1 Observation Scale Wavelength Frequency (Hz) 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, Dave Dewhurst and Ben Clennell CSIRO Earth Science and Resource Engineering Shale Research Consortium

2 Motivation: Anisotropy of Fluid Transport Faulted reservoir Anticline reservoir B A 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.) Need to assess: Permeability anisotropy

3 Motivation: Seismic/Ultrasonic Anisotropy Affects seismic data processing, inversion and interpretation (cross-well, VSP, AVO, time-lapse, ray tracing, tomography ) Nankai accretionary wedge offshore Japan s southeast margin Source: NORSAR Need to assess: Elastic anisotropy Isotropy Vertical Transverse Isotropy Tilted Transverse Isotropy Stress-dependence Emphasis on Thomsen s δ Source: Moore et al. (2007)

4 Need for Laboratory Characterization of Rock Anisotropy for Field Applications 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 Physical Properties Laboratory Probing Techniques SEM 2-D Imaging X-Ray 3-D Tomography Water Circulation Nuclear Magnetic Resonance Triaxial Deformation Stress Anisotropy Scratching Wave Propagation nm 10-9 m m 10-6 m mm 10-3 m cm 10-2 m km m Characterization Scales

5 Anisotropy & Heterogeneity: Scale-Dependent Concepts?

6 Evidence of Structural Anisotropy: High-Resolution Characterization (µm scale)

7 Evidence of Structural Anisotropy: High-Resolution Characterization (µm scale)

8 Low-Resolution Structural Characterization (mm to cm scale) Medical CT Scanner: Sample heterogeneity at mm scale A-A B-B 80 mm 80 mm 3D - High CT Contrast 3D - Low CT Contrast

9 Anisotropy of Fluid Transport

10 Anisotropy of Water Permeability (cm) Pressure Cell

11 Testing Protocol: Constant Pressure Drop Method PROTOCOL: 1. Saturate: Pc = 20MPa Pp = 10MPa 2. Impose: Pp U = 15MPa Pp D = 10MPa 3. Monitor Injection Rate: Q Q Permeability in flow direction (cm scale)

12 NMR Method: Field Gradient Method Magnetic field gradient along Y-axis

13 Perpendicular to Bedding Scaled Gradient Intensity 0 Scaled Amplitude of NMR Signal T2 Relaxation Time [µs]

14 Parallel to Bedding 1 Scaled Gradient Intensity 0 Scaled Amplitude of NMR Signal T2 Relaxation Time [µs]

15 Parallel to Bedding 2 Scaled Gradient Intensity 0 Scaled Amplitude of NMR Signal T2 Relaxation Time [µs]

16 Peak NMR Amplitudes Scaled Gradient Intensity 0 Scaled Amplitude of NMR Signal T2 Relaxation Time [µs]

17 Anisotropy of Water Diffusivity (nm to µm) 160 Fast Diffusion Fit Double Exponential Function to NMR Signal Peaks Peak Amplitude of NMR Signal 115 Water diffusivity proportional to slope of the tangent Fast Diffusivity (Free water) D h // / D h 1.5 Slow Diffusion Slow Diffusivity (Clay-Bound Water) ~ Squared Gradient Intensity (x10 6 )

18 Permeability and Diffusivity Anisotropies over Different Scales Parameter // / Scale Effective Pressure Permeability k 9.1 cm 7.5 D h = Diffusivity D h 1.5 nm-µm 0 S k Pressure vessel within magnetic field currently tested

19 Anisotropy of Seismic Properties

20 Specimen Instrumentation: Strain and P-wave (Group/Ray) Velocities 80 mm Viton Sleeve transducers = 5 mm f central ~ 0.5 MHz

21 Over-Consolidated Triaxial Loading

22 Seismic Data Processing Assumption: Bedding/T.I. symmetry plane is horizontal 25 different Azimuth angles 17 different Dip angles ~ 90 different ray paths Fit Thomsen s weak anisotropy model to V P (dip) V P ( θ ) α 1+ δ sin ( θ ) cos ( θ ) + ε cos ( θ ) θ = Dip Angle α = V P ( 90 ) ( )

23 Group Velocities Function of Dip Angle: A Snapshot Average of n experimental points with identical dip angle Fitted Thomsen s model 95% Confidence interval

24 Effect of Water Saturation

25 Effect of Isotropic Stress

26 Anisotropy of Mechanical Properties

27 Mechanical Anisotropy M // / M = 0.54 No apparent difference between axial and radial strains Differentiation between axial and radial strains

28 Effect of Stress Anisotropy

29 Effect of Stress Anisotropy

30 Effect of Stress Anisotropy (Triaxial): Low-Resolution Characterization (mm to cm scale) Axial Loading A-A B-B A-A B-B

31 (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

32 Acknowledgement of support from: BG Group Chevron ConocoPhillips ExxonMobil Sinopec Statoil Total Questions?

33 Effect of Stress Anisotropy (Triaxial): Low-Resolution Characterization (mm to cm scale) Axial Loading A-A B-B Shear Failure Tensile Failure Stress Unloading