1
C.H. Sondergeld1, K.E. Newsham2, J.T. Comisky2, M.C. Rice2, and C.S. Rai1
1Mewbourne School of Petroleum and Geological EngineeringUniversity of Oklahoma
2Apache Corp
Petrophysical Considerations in Evaluatingand
Producing Shale Gas Resources
SPE Unconventional Gas Conference, 23-25 Feb, Pittsburg Pennsylvania
2
Increasing Scale
ParticleMotion
Storage
Capacity
Sorption Diffusion Darcy Pipe =SlippageBrownian
Nano-Porosity Interparticle-Porosity Wellbore =Fracture Porosity
Flow
Capacity
ElectrochemicalGradients
Random vibration
Viscous
Flow
Type
Pore
Type
1 micron
Hydraulic
Fracture
10 0.1 0.001Free molecularflow
ContinuumFlow
SlippageFlow
TransitionFlow
KnudsenFlow
Regime
Exploitation of Gas Shales Involves Gas Flow at Many Scales
Ultimate supply is governed by flow at the smallest scales.
3
Pore sizes from NMR and SEM imaging
Ion-milling- SEM backscattered image
Moncrieff, 2009
2
1 3S
T V r
0.05 m ms
free
capillary
claybound
3 100r nm to nm
NMR and SEM agree!
4
Parameter Desired Result
Dehydration Effects (Sw) < 40% SwDepth Shallowest Depth in Dry gas Window
Fracture Fabric and Type Vertical vs. horizontal orientationOpen vs. Filled with silica or calcite
Gas Composition low CO2, N, and H2SGas-Filled Porosity (Bulk volume gas) > 2% Gas Filled Porosity
Gas type (biogenic, thermogenic, or mixed) Thermogenic
Internal Vertical Heterogeneity Less is betterMineralogy > 40% Quartz or Carbonates
< 30% ClaysLow expandablilty
Biogenic vs. detrital silicaOGIP (free and sorbed) > 100 BCF/section
Permeability > 100 nanoDacryPoisson's Ratio (static) < 0.25
Pressure > 0.5 psi /ftReservoir Temperature > 230 F
Seals Fracture Barriers Present Top and BaseShows High gas Readings-ProductionStress < 2000 psia Net Lateral Stress
Thermal Maturity Dry gas window > 1.4 RoThickness > 30 m
Total Organic Content (and Type) > 2%Wettability Oil prone wetting of kerogen
Young's Modulus > 3.0 MMPSIA
Desirable Gas Shale Characteristics
5
Compositional Variation in Shales (limey system)
TransmissionFTIR
16 minerals
6
Compositional Variations in Shales
FTIR predict more clay and less quartz! Better agreement with logs andpoint counting.
We
igh
t%
7
TOC from Logs: Modified Passey Method
• Passey method under predictsTOC in mature and over-maturegas shale
• Use Multiplier ‘C’
• This example …
Vro = 2.2, LOM = 14.5, max ∆logR = 1.0
Predicted TOC =
∆ logR x 10(2.297 – 0.1688 x LOM) x C
TOC∆ logRLOM
Un-Modified Passey Passey with C = 4
8
Brittleness from Composition and Velocities
Vp&Vs EMatched Mineralogy
Brittleness Index= (Qtz / (Qtz + Carb + Clay)
BRITTLENESS INDEX= (Ebrit + brit)/2
Ebrit = ((E-1)/(8-1))*100brit= ((-0.15)/(0.4-0.15))*100
(Rickman et al. 2008)
Brittleness fromcomposition similar to
that from sonic logs
9
Intrinsic properties should not dependon sample size.
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
0.1 1 10 100
K,
md
particle size, mm
sh-12 sh-05
Shale
Cui et al. 2009Luffel et al. 1993
nd
d
TGA_FTIR Data for Shales
• Equilibration time iscomposition dependent but<300 minutes
• Only water detected
100 oC27 oC
100 oC
100 oC
42 oC
72 oC
100 oC 1 hr
3 hr
6 hr
9 hr
H2O
Removes residual hydrocarbonsand water but retains TOC,matrix, and clay bound water.Useful in determining heattreatment before porosity andpermeability measurements.
11
Porosity Comparison
2435.00
2440.00
2445.00
2450.00
2455.00
2460.00
2465.00
2470.00
2475.00
2480.00
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
De
pth
,m
As Received Core Porosity,%
Lab 1 Lab 2 Lab 3
2435.00
2440.00
2445.00
2450.00
2455.00
2460.00
2465.00
2470.00
2475.00
2480.00
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
De
pth
,m
Dry Core Porosity,% BV
Lab 1 Lab 2
“As Received” Comparison Dry Comparison
Wide variation in simple properties among labs, greater than a factor of 2 onas received samples. Real or procedural?
12
Grain Volumes measured by two labs
2.00
2.20
2.40
2.60
2.80
3.00
2.00 2.20 2.40 2.60 2.80 3.00
La
b2
AR
Bu
lkD
en
sity,
gcc
Lab 1 AR Bulk Density, gcc
2.40
2.50
2.60
2.70
2.80
2.90
2.40 2.50 2.60 2.70 2.80 2.90
La
b2
AR
Gra
inD
en
sity,
gcc
Lab 1 AR Grain Density, gcc
“As Received” Bulk Density “As Received” Grain Density
Bulk volume measurement is consistent, whereas grainvolume measurement is different. This produces differencesin reported porosities.
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1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
0.1 1 10 100
K,m
d
particle size, mm
sh-12 sh-05
1.0E-12
1.0E-09
1.0E-06
1.0E-03
1.0E+00
0 5 10
Porosity, %
k,
md
crushed
barnett
crushed2
BC-CA
marcellus
Y_gs
syn
Gas Shale Permeability
After Cui et al. 2009
Strong particle size dependence
After Wang and Reed, 2009
Wide range in measured permsreflecting techniques and sampling ?
nd
d
pd
d
nd
14
Composite of TRA permeabilities and porositiesfor a number of gas shales.
Very limited dynamic range. Shales from Canada, Illinois, Texas and Arkansas
0.001
0.01
0.1
1
10
0 5 10 15
k,m
d
Porosity, %
TRA-GasShale
hr1
b1
b2
b3
b4
sws
swgh
swgm
ofr
rl1
d
15
Pressure dependence of shale permeability:
0.0001
0.0010
0.0100
0.1000
1.0000
10.0000
100.0000
0 10 20 30 40 50 60
k,m
d
Pconf, MPa
A B C Y1 y2 y3 y4 y5 wel pier
K
d
nd
16
Pressure dependence suggest microcrack influence
Walsh’s theory (1981) predicts linear dependence in this variable space. Singlesmooth plane in Al2O3 is the upper bounding red line. All other plugmeasurements including “whole” plugs and fractured shales fall below this.
13 2
1 lno o o
k h P
k a P
fracturedsurfaces
17
0
10
20
30
40
50
60
70
80
90
0 10 20 30 40
Yo
un
g's
Mo
du
lus
,E
,G
Pa
Pressure, MPa
v
h
45
Zun
Pathi
Enz
h1
h2
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0 10 20 30 40
n
Pressure, MPa
v
h
45
Zun
Pathi
Enz
h1
h2
Elastic Properties (Young’s modulus, Poisson’s ratio)
Wide range in mechanical properties driven by anisotropy and composition.
Horiz45o
Horiz45o
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Anisotropy
p-wave anisotropy
Both approach 30-50% in gas shales!
2 2
22
p _h p _v
p _v
v v
v
2 2
22
s _h s _v
s _v
v v
v
Consistent with mechanical properties, Young’s modulus anisotropy!
Symmetry TI to Orthorhombic
0
0.1
0.2
0.3
0.4
0.5
0 0.1 0.2 0.3 0.4 0.5
Barnett
Floyd
1:1
s wave anisotropy
horizontal
45o
vertical
19
0
1
2
3
4
5
0.5 1 1.5 2 2.5 3
Eh/Ev
nxy
/ nzx
FloydBarnettBaxter
Effect of Anisotropy on Closure Stress
xy =0.25, zx= 0.375 and Eh = 2Ev produces a h = v
Frac containment becomes difficult!
1H zx
h v
v xy
E
E
Austin Slate
0
100
200
300
400
500
600
700
0 20 40 60 80 100
Angle
Fa
ilu
reS
tre
ng
th,M
Pa
.
40k
30k
20k
10k
5k
20
2435.0
2440.0
2445.0
2450.0
2455.0
2460.0
2465.0
2470.0
2475.0
2480.0
0.0 20.0 40.0 60.0 80.0 100.0
De
pth
,m
AR Water Saturation
Lab 1 Lab 2 Lab 1 Sw Corrected to Lab 2 Porosity
Saturation changes with heating and time
Saturation estimates areaffected by accuracy ofporosity measurements
Mavor, 2009
21
Mineralogy varies considerably in a particular shale
TOC estimation by Passey et al. (1990) method works well with a multiplier
Logs require independent mineralogy calibration , FTIR fast and sufficient
Core handling and preparation needs to be standardized
Permeability on crushed samples reflect grain size more than matrix perms
Permeability measurements on cores display a strong crack component
Variable salinities render Archie saturation calculations questionable
Anisotropy is strong (30-50%) and influences closure stress estimatesand fracture containment
Recommend a committee to create standards and protocols for shale measurementsrevisit the GRI recommendations, we can’t afford to crush ¾ lb of shale!
Conclusions and Recommendations