Rock Physics of Shale - Stanford University

Rock Physics of Shale 

Gary Mavko – Stanford Rock Physics Laboratory 

1

First Question: What is Shale? 

Shale -- a rock composed of mud-sized particles, such as silt and 

clay (Boggs, 2001). This most general classification is based on 

particle size, not composition. 

Variations in usage: 

• Shale is sometimes used to refer only to fissile rocks made of 

mud-sized particles, while 

• Mudstone is sometimes used to refer to non-fissile rocks made 

of mud-sized particles, and 

• Siltstone is sometimes used for rock with mud-sized particles, 

but low clay fractions. 


2

What is Shale? 

Wentworth Scale of grain size 

φ = −log 2 d 

€ 

Mud 

( d < 30 µm) 

€ 

Grain size 

(mm) 

φ 


3

Shales vary tremendously in composition! 

4 

Gary Mavko – Stanford Rock Physics Laboratory

Organic-Rich Shale 

5 


Organic-Rich Shale 

Organic-rich shales are composed of mixtures of 

inorganic and organic materials. The inorganic 

fraction can include clay, silt, carbonate, pyrite, 

etc. The organic fraction (kerogen) appears as 

nano-size particles, called macerals, and 

hydrocarbons. 

In some cases organics appear as inclusions in 

the inorganic background, and other times, the 

inverse. 

Vanorio et al., June 2008, The Leading Edge. 

Confocal Laser Scanning Microscope image of 

an organic-rich shale. Monterey Formation. 


6

What the heck is shale porosity/permeability? 

• Network of permeable kerogen? 

• Inter-granular pores? 

• Micro/nano fractures? 

• Does hydrocarbon move via Darcy flow or molecular diffusion? 


Wang, et a., SPE 124253 


7

Porosity in Organic-rich Shale 

Nano-scale image of pores within Kerogen. 

Wang, et a., SPE 124253 


8


Fossil fragment with micropores 

Nanopores around in-organic grains. 

Intergranular micro and nano-pores 

Nanopores in organic material. 

Loucks, et al.,, Journal of Sedimentary Research, 2009, v. 79, 848–861 


9


Nanopores in organic material. 

Loucks, et al.,, Journal of Sedimentary Research, 2009, v. 79, 848–861 

10 



. 

Loucks, et al., Journal of Sedimentary Research, 2009, v. 79, 848–861 

Nanopores in organic matter. 

Loucks et al. observe that organic 

porosity increases with maturity. 

Diameter of CH 4 ~ 0.4 nm 

Methane 

11 


Organic-rich Shales, Imaging and Nanoindentation 

Ahmadov, et al., The Leading Edge, January 2009. 

12 


Kerogen Moduli Inferred from Nanoindentation 

€ 

Y 

µ 

Plausible 

Poisson’s Ratio 

K 

M 

Ahmadov, et al., The Leading Edge, January 2009. 

13 


Change of texture with maturity 

Mature Bakken Postmature Bakken 

Ahmadov, 2011, Ph.D. Dissertation, Stanford Univ. 

14 


Example Compositions 

Mineral Barnett (%) Marcellus (%) 

Quartz 35-50 10-60 

Clays (mostly illite) 10-50 10-35 

Calcite, dolomite, 

siderite 

0-30 3-50 

Feldspars 7 0-4 

Pyrite 5 5-13 

Phosphate, gypsum trace trace 

Mica 0 5-30 

A Comparative Study of the Mississippian Barnett Shale, Fort Worth Basin, and Devonian Marcellus Shale, Appalachian 

Basin, Bruner and Samosna, DOE/NETL-2011/1478. 

15 


Example Compositions 

16 


What parameters are we interested in? 

Quantity: Two rocks with the same TOC … 

Dead 

Carbon 

TOC 

Live Carbon 

Live 

Carbon 

H/C = 1.15 H/C= 0.75 

Dead 

Carbon 

… but different Hydrocarbon-Generative Potential 

17 



maturation 

gas window 

Quality; Maturity 

very oil prone 

oil prone 

inert 

gas prone 

oil window ca. 60–160 o C 

gas window ~ 150-200 o C 

Alginite: Fresh-water algae 

Exinite: Pollen, spores 

Cutinite: Land-plant cuticle 

Resinite: Land-plant resins 

Liptinite: land-plant lipids, 

marine algae 

Vitrinite: Land woody and 

cellulose materials 

Van Krevelen 

Diagram 

18 



maturation 

Quality; Maturity 

very oil prone 

oil prone 

inert 

gas prone 

Type II marine shales give 

most production 

High maturity gives better 

gas delivery 

It has been suggested that 

shale in the gas window has 

more gas and improved gas 

mobility – modified pore 

structure? Reduced kerogen 

volume? Microcracks? 

Bob Cluff (SIPES 1832) SIPES 2009 

Annual Meeting, Hilton Head, S.C. 

19 


Vitrinite is a type of maceral with a shiny appearance resembling glass (vitreous). It is formed 

diagenetically by the thermal alteration of lignin and cellulose in plant cell walls. Chemically, 

it is composed of polymers, cellulose and lignin. It is therefore common in sedimentary rocks 

with a terriginous origin, containing plant matter. 

Vitrinite Reflectance, R o : percentage of light reflected from polished vitrinite samples, 

usually at wavelengths of 546 nm. R o is sensitive to temperature ranges that are responsible 

for hydrocarbon maturation; R o increases with thermal maturity of a source rock. 

20 


€ 

Passey’s 1 Method of TOC Estimation 

DlogR = log 10(Rd/Rd baseline)+0.02*(dtc − dtc baseline) 

(2.297−0.1688LOM ) 

TOC = DlogR*10 

Rd = deep resisitivity (ohm-m) 

Rd baseline = deep resistivity in non-source shale 

dtc = sonic (usec/ft) 

dtcbaseline = sonic in non-source rock 

LOM = level of maturity 

TOC = total organic carbon (weight fraction) 

Sondergeld 2 et al find that Passey sometimes underpredicts TOC in 

mature and overmature gas sand 

1. Q. R. Passey, S. Creaney, J. B. Kulla, F. J. Morettand J. D. Stroud, AAPG Bulletin, V. 74, P 1777-1794, 1990 21 

2. Sondergeld et al., SPE Unconventional Gas Conference, 23-25 Feb, Pittsburg Pennsylvania 


Scale sonic and resistivity where 50 usec/ft 

equal 1 decade resistivity (ohm-m) 

22 


The method employs the overlaying of a properly scaled porosity log 

(generally the sonic transit time curve) on a resistivity curve (preferably a 

deep-reading tool). In water-saturated, organic-lean rocks, the two curves 

parallel each other and can be overlain, since both curves respond to 

variations in formation porosity; however, in either hydrocarbon reservoir 

rocks or organic-rich non-reservoir rocks, a separation between the curves 

occurs. The separation in organic-rich intervals results from two effects: the 

porosity curve responds to the presence of low-density, low-velocity kerogen, 

and the resistivity curve responds to the formation fluid. In an immature 

organic-rich rock, where no hydrocarbons have been generated, the 

observed curve separation is due solely to the porosity curve response. In 

mature source rocks, in addition to the porosity curve response, the resistivity 

increases because of the presence of generated hydrocarbons. The 

magnitude of the curve separation in no-reservoirs is calibrated to total 

organic carbon and maturity, and allows for depth profiling of organic 

richness in the absence of sample data. This method allows organic richness 

to be accurately assess in a wide variety of lithologies and maturities using 

common well logs.” 

23 


LOM (maturity) Estimation from R0 

24 


What’s the Shale-Gas Geoscience Question? 

Porosity 

Matrix Perm 

Overall goal: high-flow gas wells in shale! 

Quartz,Calcite,Clay,TOC 

Content 

What determines a good (high-flow) well? 

Fractures 

Brittleness 

Tectonics 

Gas Content 

Maturity 

TOC 

Deposition 

Kerogen composition, 

Chemical & thermal history 

25 


What’s the Shale-Gas Question? 

Basin 

Model 

What can we hope to detect from measurements? 

Porosity 

Matrix Perm 

Gas Content 

TOC 

Maturity 

Fractures 

Brittleness 

Azimuthal Anisotropy 

Low density 

High resistivity 

Low impedance 

High 

Impedance 

High Ur, Low K, Th 

Uplift 

Increased 

VTI anisotropy 

26 


Shale Anisotropy 

27 


What is Anisotropy? 

A rock is anisotropic when it has properties that depend on 

direction. 

• P- and S-wave velocity 

• P- and S-wave attenuation 

• Permeability 

• Electrical resistivity 

• Thermal conductivity 

Seismic waves see anisotropy, but in a more 

complex way than permeability or 

resistivity. Seismic propagation depends on 

the direction of propagation and the 

direction of polarization relative to the 

symmetry axes of the rock anisotropy. 

We define anisotropy at the scale of the measurement 

28 


Why Worry about Anisotropy? 

• It is everywhere. 

• It affects amplitudes, traveltimes, and ray paths 

• It changes fluid substitution procedures 

• It affects the seismic signature of pore pressure 

• It responds to stress 

It might also be a diagnostic of shale properties. 

29 


Practical Challenges 

• Predict / infer anisotropy from sparse data -- e.g. well logs 

• Incorporate anisotropy in seismic acquisition and imaging. 

• Understand seismic anisotropy for seismic interpretation 

(lithology, fluids, pressure, stress) 

• Map permeability anisotropy for reservoir management. 

30 


Sources of Anisotropy 

31 


Layering Anisotropy 

This will be present in all sedimentary 

basins. Anisotropy results from the 

contrasting layers, from the intrinsic 

anisotropy within layers, from 

superimposed fractures, and from stress 

differences. 

Intrinsic fabric anisotropy 

(e.g.shale) tends to dominate 

over the layering effect. 

The Backus Average is our 

primary rock physics tool for 

layered systems 

32 


Fabric Anisotropy 

Here we show a photo of beach sand, poured into a clear 

container. Even though it is relatively homogenous and 

well-sorted, there is a subtle fabric that translates into 

seismic anisotropy. 

If you can see a fabric, then there probably is anisotropy. 

Sand photograph 

Seismic Vp vs. confining pressure 

Vega, 2003, Ph.D. Dissertation, Stanford Univ. 

Horizontal 

Vertical 



Mylonite 

horizontal 

vertical 

Jones, 1983, Ph.D. Dissertation Stanford 



Gneiss 

horizontal 

vertical 

Jones, 1983, Ph.D. Dissertation Stanford 



Shale 

horizontal 

vertical 

fast S 

slow S 

Tosaya, 1982, Ph.D. Dissertation Stanford 


Shale Anisotropy 

Sources of shale anisotropy: 

• Alignment of platy clay minerals 

• Alignment of the domains (clusters of clay) 

• Alignment of non-spherical pores and microcracks 

• Alignment of fractures at scales much larger than the grains and 

pores 

• Fine-scale lamination of shaly materials with different stiffnesses 

• Lenses of kerogen 

Shale often has VTI symmetry 

37 


Aligned Fabric Anisotropy 

Bandyopadhyay, 2009, Ph.D. dissertation, Stanford 

38 


Deposition/Compaction Hypotheses 

• Shale anisotropy should increase with effective stress/depth/compaction as clay grains 

become more and more aligned -- (Tosaya, 1982) 

• Dispersed sedimentation in a low energy environment leads to strong preferred 

orientation at the onset of sedimentation. 

• Bioturbation can randomize the texture 

• Flocculated clay aggregates have random orientation of clay particles. These aggregates 

might eventually collapse and align with compaction 

• Lab experiments seem to confirm some increase in anisotropy with compaction, but not 

to the extent of simple rock models. 

• Overpressure: disequilibrium compaction can slow alignment of grains, causing lower 

anisotropy. However, late-stage overpressure can open cracks in the fissile and increase 

anisotropy. 

Tosaya, 1982, Ph.D. Dissertation Stanford 


39 


Organic-Rich Shale Anisotropy 

Presence of organic compounds requires a low energy 

environment, a rapid burial of organic materials, and anoxic 

bottom water for the preservation of the organic material – all 

favoring fabric alignments. Elastic anisotropy in organic-rich 

rocks is well established in Geophysics literature (Vernik and 

Landis, 1996; Vernik and Liu, 1997). 


40 


Velocity Anisotropy from Thinly Layered Kerogen 

Velocities in kerogen-rich Bakken shales (Vernik, 1990) and other low porosity 

argillaceous rocks (Lo et al., 1985; Tosaya, 1982; Vernik et al., 1987). Compiled 

by Vernik, 1990. 

Stanford Gary Rock Mavko Physics – Stanford Laboratory Rock Physics - Gary Laboratory Mavko 

F.24

A negative correlation is often found between the clay fabric intensity and the 

quartz content in shale. 

Increasing 

alignment 

Data from Curtis et al., 1980. 

Clay orientation distribution from XRD. 

from: Bandyopadhyay, 2009, Ph.D. Dissertation, Stanford 

Data from Johnston and Christensen, 1995. 

Anisotropy vs. quartz fraction. 

Johnston, J. E., and N. I., Christensen, 1995, Journal of Geophysical Research B, 100, 5991–6003. 

Curtis, C. D., S. R., Lipshie, G., Oertel, and M. J., Pearson, 1980, : Sedimentology, 27, 333-339. 

42 


Velocity Sensitivity to Effective Pressure 

Vertical Vp 

Increasing 

maturity 

Vernik and Liu, 1997, GEOPHYSICS, 62, 521–532. 

Vernik, GEOPHYSICS, 1994, 59, 555-563 

Vernik and Landis, 1996, AAPG Bulletin, 80, 531–544. 


Pressure sensitivity indicates 

cracks. For these samples, 

higher maturity samples have 

more stress sensitivity. 

43 


Anisotropy Sensitivity to Pressure, Maturity 

Vp anisotropy 

Increasing 

Peff 

Vanorio et al., 2008 


Vernik, GEOPHYSICS, 1994, 59, 555-563 

Vernik and Landis, 1996, AAPG Bulletin, 80, 531–544. 


More crack anisotropy at 

higher maturity. 

Less “intrinsic” anisotropy at 

higher maturity. 

44 


Lab data: Anisotropy vs. Effective Pressure 

Colored by TOC 

Niobrara 

Vernik and Liu, 1997, GEOPHYSICS, 62, 521–532 

45 


Lab data: Anisotropy vs. Effective Pressure 

Colored by R0 

Niobrara 

Vernik and Liu, 1997, GEOPHYSICS, 62, 521–532 

46 


Vertical Fractures 

47 


Fracture Anisotropy 

48 


Fracture Permeability 

High Pp 

Natural or induced fractures can dominate shale perm; they are 

usually necessary for economically interesting flow in shale. 

These fractures also impact Vp, Vs, Vp/Vs ratio, attenuation, 

and anisotropy. 

49 


Fracture Permeability 

Low Pp 

Effective stress closes fractures, decreasing permeability and 

increasing seismic velocities. 

50 


Fractures/ 

Brittleness 

51 


Predicting/measuring Brittleness 

Brittleness increases the chances of naturally occurring fractures, as 

well as success of hydrofracs. Brittle materials accommodate strain 

(deformation) by breaking. In constrast, ductile materials 

accommodate strain by “flowing.” Not only are ductile materials less 

likely to create permeable fractures, ductile materials will also allow 

man-made fractures to close or “heal.” 

Important practical issue is how to determine geomechanical 

properties from geophysical measurements. 

52 


Brittleness: Examples 

Low Clay (tight sandstone) High Clay Fraction 

Porosity .01 

Clay .12 

Porosity .05 

Clay .31 

Porosity .05 

Clay .63 

In these examples, ductility depends on (1) composition and (2) 

confining stress. 

Brittle failure has little or no plastic flow before failure. 

Jizba, 1991, Ph.D. Dissertation, Stanford University. 

Jizba, 1991, Ph.D. 

dissertation, Stanford 

Univ. 

53 



Brittleness is a complex function of lithology, composition, TOC, 

effective stress, temperature, diagenesis, thermal maturity, 

porosity, … 

54 


Fractures Usually Prefer Certain Lithofacies 

Joint Sheared Joint 

Brittle facies often 

accommodate strain by 

fracturing, while shales 

might accommodate 

strain ductily. 

J-M. Florez, 2005. Ph.D. 

Dissertation, Stanford Univ. 


Quantifying Brittleness 

Because material failure is important in many technologies, there 

are many attempts to define or quantify a Brittleness Index, e.g. 

€ 

B 1 = σ c 

σ t 

where 

€ 

€ 

€ 

€ 

B 2 = σ c − σ t 

σ c + σ t 

σ c 

σ t 

q 

Kahraman, 2003, Engineering Geology 65 (2002) 269–283 

B 2 = qσ c 

= Uniaxial compressive strength 

= Tensile € strength 

= Amount of fines in impact test 

56 



‘Halliburton’ Brittleness Index 

€ 

( ) /2 

B = E Brit +ν Brit 

E Brit =100( E static −1) 

/ ( 8−1) 

( ) / 0.15−0.4 

ν Brit =100 ν static −0.4 

Rickman et al., 2008, SPE 115258, SPE Annual Meeting 

( ) 

57 



€ 

€ 

€ 

Because material failure is important in many technologies, there 

are many attempts to define or quantify a Brittleness Index, e.g. 

B 1 = σ c 

σ t 

B 2 = σ c − σ t 

σ c + σ t 

B 2 = qσ c 

€ 

€ 

σ c 

σ t 

q 

Kahraman, 2003, Engineering Geology 65 (2002) 269–283 

Correlate with penetration rate of rotary 

drills 

Correlates with penetration rate of percussive 

drills 

= Uniaxial compressive strength 

= Tensile strength 

= Amount of fines in impact test 

58 



In terms of overconsolidation ratio 

€ 

OCR = σ V max 

σ V 

(only valid for layered rocks and max principal stress is vertical) 

€ 

€ 

€ 

Brittleness: 

( ) OC 

( ) NC 

B = σ c 

σ c 

σ V Vertical stress 

σ V max Vertical stress at max burial 

= OCR b 

Nygard et al., Marine and Petroleum Geology 23 (2006) 201–212 

59 


Brittleness: Composition 

Composition: There is anecdotal evidence that (1) silica 

(siltiness) and (2) calcite content increase brittleness. One 

index that is sometimes quoted: 

€ 

B ( % ) = 

An intuitive extension to calcite: 

€ 

B ( % ) = 

Q 

Q + Carbon + Clay 

Q + Calcite 

Q + Calcite + Carbon + Clay 

60 


Quartz and Calcite are more brittle than clay and TOC 

Dolomite (dolostone, dolomicrite) more brittle than calcite 

61 


Brittleness: Composition 

⎛⎛ 

⎜⎜ 

⎝⎝ 

Issue: How to measure brittleness from logs? Calcite and quartz each have 

distinctly different Vp/Vs than shale. However when added, they might cancel 

changes in Vp/Vs. 

VP VS ⎞⎞ 

⎟⎟ ≤ 

⎠⎠ sand 

V ⎛⎛ ⎞⎞ P 

⎜⎜ ⎟⎟ ≤ 

⎝⎝ VS ⎠⎠ shale 

V ⎛⎛ ⎞⎞ P 

⎜⎜ ⎟⎟ 

⎝⎝ VS ⎠⎠ limestone 

Increasing 

stiffness 

Increasing Vp/Vs 

Increasing gas 

Increasing 

porosity 

62 


Poisson’s ratio Young’s Modulus (GPa) 

quartz .07 94 

calcite .31 79 

dolomite .23 121 

clay .35 36 

rubber ~0.48 .01 

copper 0.34 117 

steel 0.30 210 

glass 0.2-0.3 50-90 

cork ~0 0.03 

63 


€ 

Beware of Poor Legacy Assumptions 

€ 

σ v 

σ h 

• Sediments deform plastically 

during burial – not elastically 

• Therefore the horizontal stress is 

NOT the elastic expression: 

σ h ≠σ v 

σ h ≠σ v 

⎡⎡ ν ⎤⎤ 

⎣⎣ ⎢⎢ 1−ν ⎦⎦ ⎥⎥ 

⎡⎡ C ⎤⎤ 13 

⎢⎢ 

⎣⎣ C ⎥⎥ 

⎦⎦ 33 

64 


Modeling 

65 


€ 

€ 

Modeling Composition 

Density: 

ρ = ∑ xiρ i 

ρ = ( 1− k −φ)ρ 

mineral + kρker +φρ fluid 

k = ρb −( 1− φ) 

ρmineral − φρfluid ρk − ρmineral k ≈ ρ b − ρ mineral 

ρ k − ρ mineral 

; when φ ≤ .03 

66 


€ 

Modeling Composition 

Elastic Modulus: Voigt-Reuss-Hill average 

⎡⎡ 

K = 0.5 ∑ xiK i + ∑ xi /Ki ⎣⎣ ⎢⎢ 

⎡⎡ 

µ = 0.5 ∑ xiµ i + ∑ xi /µ i 

⎣⎣ ⎢⎢ 

( ) −1 

( ) −1 

⎤⎤ 

⎦⎦ ⎥⎥ 

⎤⎤ 

⎦⎦ ⎥⎥ 

67 


Mineral Properties 

density Bulk 

modulus 

Shear 

modulus 

Young’s 

modulus 

Poisson’s 

ratio 

quartz 2.65 37 44 94 .074 

feldspar 2.62 37 15 40 .324 

calcite 2.71 70 30 79 .313 

dolomite 2.87 75 49 120 .232 

siderite 3.96 124 51 135 .32 

clay 2.55 25 9 36 .279 

pyrite 4.93 147 133 306 .15 

kerogen 1.30 6 5 12 .19 

A Comparative Study of the Mississippian Barnett Shale, Fort Worth Basin, and Devonian Marcellus Shale, Appalachian 

Basin, Bruner and Samosna, DOE/NETL-2011/1478. 

68 


Examples 

Quartz Calcite Dolomite Clay Kerogen Pyrite E Poisson’s 

Ratio 

40 10 5 30 10 5 62 0.19 2.65 

20 10 5 50 10 5 48 0.22 2.66 

10 10 5 60 10 5 49 0.24 2.66 

10 20 5 45 15 5 50 0.24 2.60 

10 30 5 40 10 5 56 0.25 2.67 

10 20 5 50 10 5 52 0.24 2.67 

10 30 5 40 10 5 56 0.25 2.67 

10 40 5 30 10 5 59 0.25 2.67 

10 40 5 25 15 5 56 0.25 2.60 

Density 

69 


Example computed trends 

70 


Example computed trends 

71 


Density vs. Kerogen 

Lab data (Vernik and Landis, 1996), plotted as bulk density vs. kerogen volume, from samples of Bakken shale. 

The four sets of lines are labeled with the assumed kerogen density, ranging from 1.0-1.6 g/cm 3 . The four black 

lines assume the measured porosity ~0.01, and oil in the pores. The dashed red lines assume the porosity is zero. 

The dashed blue lines assume that the porosity is saturated with gas. 

72 





74 




75 


Bedding-Plane Microcracks 

Adding horizontal cracks tends to decrease velocities – depends on fluid. 

Wet cracks 

Gas-filled cracks 

76 



Adding horizontal cracks modifies Vp/Vs – depends on fluid. 

Wet cracks 


77 



Cracks modify intrinsic anisotropy. 

Wet cracks 


78 



Velocities vs. angle of incidence. 

Wet cracks 


79 


Vertical Fracture Modeling 

Observed: 

Strong travel time anisotropy, 

not much amplitude variation 

Reduced travel time anisotropy, 

subtle amplitude variation 

small travel time anisotropy, 

more amplitude variation, 

Early troughs are stretched 

Azimuth From Fracture Normal 

80 


Vertical Fracture Modeling 

Interpretation 

Heavily 

fractured, 

brine 

Rotated 

minimal 

fractures 

No 

fractures 

Heavily 

fractured, 

brine 

Brine 

Gas 

Brine 

Fracture 

strike 

Brine 

Fracture 

strike 

Fracture 

strike 


81 


Vertical Fracture Modeling -- Amplitude 

Amplitude 

Brine 

Gas 

Brine 

Fracture 

strike 

Brine 

Fracture 

strike 

Fracture 

strike 


S08bSM07bM-0bBR0E-09b.tif 

82 


Vertical Fracture Modeling -- NMO 

Travel time 

Brine 

Gas 

Brine 

Fracture 

strike 

Brine 

Fracture 

strike 

Fracture 

strike 


S08bSM07bM-0bBR0E-09b.tif 

83 


Summary 

• Shale is defined by particle size. 

• Shale can have a very large range of compositions. 

• Shale can have a large range of P- and S-wave velocities 

- Composition 

- Porosity 

- Effective stress 

- Compaction 

• Shale Vp/Vs depends on composition, especially relative 

amounts of clay, silt, organics, and carbonate 

• Shale can have a large range of anisotropies 

- Small if bioturbated 

- Large if a pronounced fabric 

- Silt and cementation can reduce anisotropy 

• In kerogen-rich shales, properties depend on composition, TOC, 

and maturity, and fracatures. 

84 


Issues 

• Shale lab data are sparse, compared with sandstone and 

carbonate. 

• Logs are also more common in reservoirs than shales. 

• Other than models like soft-sediment and Raymer, we don’t 

have any comprehensive shale models. 

• Shale anisotropy depends on many factors and is difficult to 

predict. 

• Organic shales (oil shale and gas shale) can have a range of 

properties, depending on composition, TOC, maturity. 

• For gas and oil shales, it is not clear what the geophysical 

questions are: 

- TOC? 

- Maturity? 

- Geomechanical? 

85

Rock Physics of Shale - Stanford University

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