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

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~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

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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