Characterizing Matrix Permeability and Porosity in Barnett Shale
Peter Polito, Athma Bhandari, & Peter Flemings Bureau of Economic Geology, The University of Texas at Austin
Outline 1. Key points 2. Motivation 3. Barnett characterization 4. Experimental permeability and porosity
a. Permeability and porosity methods b. Permeability results c. Multi-scale behavior d. Porosity results
5. Experimental insights 6. Problems and challenges
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Key Points
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Permeability anisotropy Flow parallel to bedding ~1x10-19 m2 Flow perpendicular to bedding ~2x10-21 m2
Stressed porosity in flow-parallel sample decreases from 7.0% to 5.3% with increasing stress
Helium and stressed (argon) porosity values generally agree
More work is needed to better understand the relationship between crushed and whole plug permeability and porosity
Motivation
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Motivation
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Wide variation in our understanding of matrix permeability
Barnett Characterization
2336 m
2344 m
Loucks & Ruppel, AAPG 2007
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Barnett Characterization
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Parameter Value
TOC 3.9 %wt
Thermal maturity 1.89 % R0
3.8 cm
bedding
Pulse-decay Permeability Method
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Pulse-decay Porosity Method
880
920
960
1000
1040
1080
1120
0 2 4 6 8 10
Por
e P
ress
ure,
Pp
(psi
a)
Time
Pu1
Pf
Pi
Upstream pressure
Downstream pressure
Vus1 Vus2 Vds Vp
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%
Helium Porosity
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%
Vr Vc
Vp
Stress states
The challenge of studying low permeability materials
10.3 MPa
6.9 MPa
17.2 MPa
27.6 MPa
41.4 MPa
Pc
Pp
Stress state 1
Stress state 2
Stress state 3
Stress state 4
Pre
ssur
e
Pulse decay test sequence
Pp
Pc
~4 days ~4 days ~4 days ~4 days
Argon gas
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Pulse-decay Permeability Method
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k : Sample permeability [m2] c : Gas compressibility = 1/avg. pore pressure [Pa-1] µ : Gas viscosity [Pa s] φ : Core plug porosity [-] L : Core plug length [m] s : Pressure decay slope[s-1] a : Ratio of pore to upstream reservoir volume b : Ratio of pore to downstream reservoir volume
(Hsieh et al. 1981; Dicker & Smits, 1988; Jones, 1997)
( )2
,c L skf a bµφ
=
( ) ( ) ( )321, ( 0.4132 ) 0.0744 0.05783
f a b a b ab a b ab a b ab= + + − + + + + +
Upstream pressure
Downstream pressure
∆P0
∆P Pp, av
k = 2.3e-21m2 k = 2.3 nD
Barnett 2V : permeability vs. stress
The challenge of studying low permeability materials
~42 hrs
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Bhandari et al., in review
Pc-Pp (MPa)
0 5 10 15 20 25 30 35 40Pe
rmea
bilit
y (m
2 )0
5e-22
1e-21
2e-21
2e-21
3e-21
3e-21
Pc-Pp (psi)
0 10002000
30004000
5000
Perm
eabi
lity
(nd)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
The challenge of studying low permeability materials
Barnett 6H1: Permeability
kh = 9.7x10-20 m2
kv = 2.3x10-21 m2
25 hrs
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Bhandari et al., in review
Barnett 6H1 : permeability vs. stress
The challenge of studying low permeability materials
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Bhandari et al., in review
Pc-Pp (MPa)
0 5 10 15 20 25 30 35 40
Perm
eabi
lity
(m2 )
0.0
2.0e-20
4.0e-20
6.0e-20
8.0e-20
1.0e-19
1.2e-19
Pc-Pp (psi)
0 10002000
30004000
5000
Perm
eabi
lity
(nd)
0
20
40
60
80
100
120
The challenge of studying low permeability materials
Barnett 6H1: Multiscale behavior
25 hrs
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Bhandari et al., in review
Time (min)0.01 0.1 1 10 100 1000 10000
Pres
sure
(MPa
)
6.4
6.6
6.8
7.0
7.2
7.4
7.6
Multiscale behavior
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Layering with higher TOC
Barnett permeability summary
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6H1
2V
Bhandari et al., in review
Barnett permeability summary
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6H1
2V
2V (GRI)
6H1 (GRI)
Bhandari et al., in review
Barnett permeability summary
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6H1
2V
2V (GRI)
6H1 (GRI)
Vermylen, 2011
Bustin, 2011
Kang et al., 2011
Kang et al., 2011
Bhandari et al., in review
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3.03.54.04.55.05.56.06.57.07.58.0
-1000 0 1000 2000 3000 4000 5000 6000
Poro
sity
, ᶲ (%
)
Effective confining pressure, Pc- Pp (psia)
6H1 stressed porosity
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3.03.54.04.55.05.56.06.57.07.58.0
-1000 0 1000 2000 3000 4000 5000 6000
Poro
sity
, ᶲ (%
)
Effective confining pressure, Pc- Pp (psia)
6H1 stressed porosity
6H1 HeP
2V HeP
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3.03.54.04.55.05.56.06.57.07.58.0
-1000 0 1000 2000 3000 4000 5000 6000
Poro
sity
, ᶲ (%
)
Effective confining pressure, Pc- Pp (psia)
6H1 stressed porosity
6H1 HeP
2V HeP
2V GRI
6H1 GRI
Insights from permeability measurements
Vertical permeability ~2 x10-21 m2
Horizontal permeability ~1 x10-19 m2
GRI permeability ~ 1x10-19 m2 (Core 2) Stress dependence on permeability comparable to
previous studies and is caused by: Pore throat decrease Closing of fractures (nano-scale)
Multi-scale permeability is result of: bedding or nanometer-scale fractures/damage (invisible to CT)
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Insights from porosity measurements
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Stressed porosity is comparable to helium and GRI porosity in sample 6H1 Modeling results show
40-45% of porosity in high-permeability layers or fracturing 55-60% of porosity in low-permeability layers or matrix
Helium and GRI porosity do not agree in sample 2V
Problems and challenges
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Acquiring unfractured shale plugs At our best, we can identify fractures >25 µm using CT Plugging success rate is ~10%
Testing duration To fully characterize a sample across multiple stress states, test
durations can stretch to months
Stressed porosity Interpreting pulse decay data to estimate stressed porosity
yields promising results but with greater uncertainty
References
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Bhandari, A.R., Flemings, P.B., Polito, P.J., Cronin, M.B., and Bryant, S.L., Anisotropy and stress dependence of permeability in the Barnett Shale: Transport in Porous Media, in review.
Brace, W.F., Walsh, J.B., and Frangos, W.T., 1968, Permeability of granite under high pressure: Journal of Geophysical Research, v. 73, p. 2225-2236.
Bustin, A.M., Cui, X., Ross, D.J.K., Pathi, V.S.M.: Impact of shale properties on pore structure and storage characteristics. SPE paper 119892 presented at the SPE Shale Gas Production Conference held in Fort Worth, Texas, 16–18 November 2008. doi:10.2118/119892-MS
Dicker, A.I., and Smits, R.M., 1988, A practical method for determining permeability from laboratory pressure-pulse decay measurements: SPE 17578, p. 285-292.
Hsieh, P.A., Tracy, J.V., Neuzil, C.E., Bredehoeft, J.D., and Silliman, S.E., 1981, A transient laboratory method for determining the hydraulic properties of tight rocks. 1. Theory: International Journal of Rock Mechanics and Mining Sciences, v. 18, p. 245-252.
Jones, S.C., 1997, A technique for faster pulse-decay permeability measurements in tight rocks: SPE Formation Evaluation, p. 19-25.
Kang, S.M., Fathi, E., Ambrose, R.J., Akkutlu, I.Y., Sigal, R.F., 2001: Carbon dioxide storage capacity of organic-rich shales. SPE Journal, SPE 134583, 16(4), 842-855. doi: 10.2118/134583-PA
Loucks, R.G., and Ruppel, S.C., 2007, Mississippian Barnett Shale: Lithofacies and depositional setting of a deep-water shale gas succession in the Fort Worth Basin, Texas: AAPG Bulletin, v. 91, p. 579-601.
Vermylen, J. P., 2011: Geomechanical Studies of the Barnett Shale, Texas, USA. PhD Thesis, Stanford University, Palo Alto, California, 143 pp.
Acknowledgments
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Collaborators: Drs. Steve Bryant, Hugh Daigle, Julia Reece, Kitty Milliken
Graduate Students: Michael Cronin, Chunbi Jiang
Industry Partner: Shell Oil
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