0 2 4 6 8 10 12 140

0.5

1

1.5

2

2.5

3

Effective Stress(MPa)

Per

mea

bili

ty(m

d)

Permeability VS Peff

HeCH

4CO

2

0 2 4 6 8 10 12 140

0.5

1

1.5

2

2.5

3

Effective Stress(MPa)

Perm

eab

ility

(md

)

Permeability v.s. Peff

HeCH

4CO

2

0 2 4 6 8 10 12 140

0.5

1

1.5

2

2.5

3He

Effective Stress(MPa)

Perm

eab

ility

(md

)

086!He!adsorption086!He!desorption079!He

0 2 4 6 8 10 12 140

0.5

1

1.5

2

2.5

3

CH4

Effective Stress(MPa)

Perm

eab

ility

(md

)

086!CH

4!adsorption

086!CH4!desorption

079!CH4

0 2 4 6 8 10 12 140

0.5

1

1.5

2

2.5

3

CO2

Effective Stress(MPa)

Perm

eab

ility

(md

)

086!CO

2!adsorption

086!CO2!desorption

079!CO2

0 2 4 6 8 100

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Effective Stress

Perm

eabi

lity

k=1

Pp

=1MPa

Pp

=3MPa

Pp

=6MPa

Pp

=8MPa

0 2 4 6 8 100

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Effective Stress

Perm

eabi

lity

k=0.6

Pp

=1MPa

Pp

=3MPa

Pp

=6MPa

Pp

=8MPa

0 2 4 6 8 10 12 14 16 180

0.002

0.004

0.006

0.008

0.01

0.012

0.014

Time (hours)

Volu

met

ric S

trai

n (s

hrin

kage

)

Creep!087, P c=13MPa, P p=1MPa

HeN

2CH

4CO

2

0 1 2 3 4 5 6 7 8 9 10!0.07

!0.06

!0.05

!0.04

!0.03

!0.02

!0.01

0

0.01

0.02

0.03

Pore Pressure (MPa)

Swel

ling

Shrin

kage

Introduction Effects of Adsorbed Gases on the Physical and Transport Properties of Low-­Rank Coal, PRB, WY: Implications for Carbon Sequestration and Enhanced Coalbed Methane Recovery

Yi Yang1*, Mark Zoback11Department of Geophysics, Stanford University, Stanford, CA 94305, *alecyang@stanford.edu

Motivation

Sample Location and Discription

Experiment Setup

In this study we examine the adsorption of He, N2, CH4 and CO2 on the mechanical and flow properties of sub-­bituminous coal from the Powder River Basin, Wyoming. Lab measurements were conducted on one-­inch diameter core samples of coal under hydrostatic conditions. The coal samples were vacuum dried before each test, then saturated by a test gas until steady state was reached. Measurements of adsorption, swell-­ing strain, elastic stiffness, creep strain and permeability of both intact and crushed samples were carried out at a series of either increasing pore pressure or increasing effective stress. Our results show that the ad-­sorption of CO2 is much larger than CH4, which is larger than N2. Hyster-­esis is observed among pure component adsorption and desorption iso-­therms which are Langmuir-­type adsorption isotherms. Permeability shows a moderate decrease with increasing effective stress for He, CH4 and CO2. At constant effective stress, permeability decreases when the saturating gas changes from He to CH4 and CO2. Hysteresis of perme-­ability with increasing and decreasing effective stress is not observed in crushed samples. The coal swells when CH4 displaces He and swells more when CO2 displaces He. The same is true of viscoplastic creep. Vis-­coplastic creep is greater in the presence of CH4 than He and more with CO2 than with CH4.

Origin: PRB, WY, Fort Union Forma on, Roland and Smith Coal Zone

Rank: sub-­‐bituminousMicrofracture and cleatsSo , easy to break

Origin: PRB, Montana, Wyodak-­‐Anderson coal zone

Rank: sub-­‐bituminousMicrofracture and cleatsHard (as rock)

Origin: PRB, WY, Surface Mining

Rank: sub-­‐bituminousMicrofracture and

cleats

House A

ir

Oil

Axial

Command

Con!ning

Data

Gas

Quizix

Quizix

Adsorp on and Swelling of Coals

-­‐ Volumetric Method

Mechanical Proper es of Coals

-­‐ Stress and Strain

-­‐ Ultrasonic P and S wave veloci es

Flow Proper es of Coals

-­‐ Darcy Flow

Velocity Coreholder

Coal Sample Viton and Copper

Adsorption and Swelling

0 1 2 3 4 5 6 7 8 90

10

20

30

40

50

60

70

80

Pore Pressure (MPa)

Adso

rptio

n (c

c/g)

0 1 2 3 4 5 6 7 8 9 100

2

4

6

8

10

12

14

16

18

20

22

Pore Pressure (MPa)

Sorp

tion

(cc/

g)

N2!ads

N2!des

CH4!ads

CH4!des

CO2!ads

CO2!des

Adsorption Effects on the Mechanical Properties

Adsorption Effects on the Transport Properties

Adsorption of CO2 is much larger than CH4, which is larger than N2, for both intact and crushed coal samples.

Hysteresis is observed among pure component adsorption and de-­sorption isotherms which are Langmuir-­type adsorption isotherms.

Permeability shows a moderate decrease with increasing effective stress for He, CH4 and CO2.

At constant effective stress, permeability decreases when the satu-­rating gas changes from He to CH4 and CO2.

The coal swells when CH4 displaces He and swells more when CO2 displaces He.

Viscoplastic creep is greater in the presence of CH4 than He and more with CO2 than with CH4.

0 5 10 15 20 250

2

4

6

8

10

12

14

Steps

Pres

sure

(MPa

)

Pore Pressure(MPa)Confining Pressure(MPa)

0 5 10 15 20 250

2

4

6

8

10

12

14

16

18

20

Steps

Pre

ssu

re (

MP

a)

Pore Pressure(MPa)Confining Pressure(MPa)

Bulk modulus of intact PRB coal samples as a functionof effective pressure. Pore pressure is constant and equal to 1 MPa. Interestingly, static bulk modulus decreases by a factor of 2 after the coal is saturated with CO2.

0

2

4

6

8

10

12

14

0 2 4 6 8 10

Bulk Modulus (GPa)

Effective Pressure (MPa)

Static and Dynamic Bulk Modulus Intact PRB Coal Samples

Static -­ Helium Static -­ CO2 Dynamic -­ Helium Dyamic -­ CO2

Static bulk modulus is determined by measuring changes in volumetric strain in response to changes in effective pressure. Dynamic bulk modulus is calculated from ultrasonic P and S wave velocities and the sample density.

Conclusions

4 5 6 7 8 9 100

2

4

6

8

10

12

14

16

18

Effecitve Pressure (MPa)

M Modulus(GPa)

6WDWLF +HOLXP

6WDWLF &2 CH4

??

??

He

CO2

CO2

Effect of CO2 and He on the P-­wave Velocity* of Coal

*As determined from Hagin and Zoback static measurements

M-­Modulus of Intact PRB coal samples as a function of effective pressure, as determined mesurement on the left.Obvious difference of M-­modulus, which larged depend on P-­wave velocity, can be detected when coal is saturated withHe and CO2 , it would be interesting to investigate the behavior when coal is saturated with CH4

0 5 10 15 20 250

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.01

Time (hours)

Volu

met

ric S

trai

n (s

hrin

kage

)

Creep!097, P c=13MPa, P p=1MPa

HeN

2CH

4CO

2

4 5 6 7 8 9 10 11 12 13!0.05

!0.04

!0.03

!0.02

!0.01

0

0.01

Confining Pressure (MPa)

Volu

met

ric S

train

He!adsHe!desN

2!ads

N2!des

CH4!ads

CH4!des

CO2!ads

CO2!des

References

Swelling During Gas Injection

0 2 4 6 8 10 12!1.6

!1.4

!1.2

!1

!0.8

!0.6

!0.4

!0.2

0 x 10 !3 Swelling(P p=1MPa, P conf=2MPa)

Time(hours)

Volu

met

ric S

trai

n (S

wel

ling)

HeCH 4HeCO 2

Permeability and Effective Stress

Volumetric Method

Swelling-­‐-­‐Crushed Coal

D ype Ash Content(%) Ro% OC

WY_1 CRUSHED -­‐-­‐ 0.31% 1.78

M CRUSHED 1.36 0.31% 56.56

WY_2 N AC 4.61 0.28% 57.58

WY_1 WY_2

2>CH4>N2 Feasibility of CO2

Effect Stress Related Sorption Induced

Reservoir Depletion-­>Pp Decrease-­>Peff Increase-­>Fracture Closure-­>Permeability Decrease

Gas Desorption-­>Matrix Shrinkage-­>Fracture Opening-­>Permeability Increase

Permeability Measurement Procedure Permeability Measurement Setup

CO2

Visco-­plastic deformation (creep) measured on crushed sample under hydrostatic conditioin, with different gas saturation.

Visco-­plastic deformation (creep) measured on intact sample under hydrostatic conditioin, with dif-­ferent gas saturation.

Creep behavior of crushed coal sample as a function of time. Pore pressure was held at 1MPa during the test, while the confining pressure was kept constant at 13MPa to main-­tain the effective stress. Lateral and axial changes of the sample was recorded to calculate volumetric strain. CO2 shows most time dependent visco-­plastic deformation.

Creep behavior of intact coal sample as a function of time. Pore pressure was held at 1MPa during the test, while the confining pressure was kept constant at 13MPa to maintain the effective stress. Lateral and axial changes of the sample was recorded to calculate volumetric strain. CO2 shows most time dependent visco-­plastic deformation.

CH4

N2

CO2

CO2

CH4

N2

He

N2

CH4

CH4

He

N2

CH4

N2He

He

N2

CH4

CH4

He

CO2

CO2

Crushed Coal

Crushed Coal

Crushed Coal

Intact Coal

Intact Coal

Intact Coal

Adsorption and corresponding swelling as a function of pore pressure. The effective stress was 3MPa during the measurement. The adsorption capacity of CO2 is much larger than CH4, which is larger than N2. The adsorption behavior of all three gases can be described as Langmiur type adosorption isotherm. The corresponding swelling is-­consistent with adsorption amount and Langmuir like.

Adsorption and corresponding swelling as a function of pore pressure. Adsorption capacity is less on intact coal comparing to crushed coal. Desorption is also measured and N2 and CH4 shows little hysteresis, while CO2 shows much difference between adsorption and desorption be-­havior. The corresponding swelling is consistent with ad-­sorption amount.

GC31B-­0885 AGU, Fall 2010,December 13th-­17th

Permeability measured as a function of effec-­tive stress, followed by a creep test

Gas flow at constant rate and pressure drop is measured to calculate permeability

Error Bar

Error Bar Error Bar

Error Bar Error Bar

CO2

1. For each gas, permeability reduces with increasing effective stress.2. Permeability reduces when saturated with CH4 and CO2.

Permeabiilty mesaured as a function of effective stress with dif-­ferent gas saturation. The injection rate is constant during the test, observation includes:

Permeability measured as a function of increasing and decreas-­ing effective stress with different gas saturation:

1. For each gas, permeability reduces with increasing effective stress.2. Permeability reduces when saturated with CH4 and CO2.3. Hysteresis is not obvious between adsorption and desorption.

Ini al Satura on

Sample saturated with He

Equilibrium

Equilibrium is achieved un l pressure stabilize

Gas Displacement

njec ng CH4 or CO2 to displace the gasPore pressure is maintained constant during injec on

Equilibrium

Equilibrium is achieved a er certain amount of me

Dynamic gas injection and corresponding swelling as a function of time. Obvious swelling is ob-­served when the saturation gas changed from He to CH4 or CO2 during gas injection process

Assumption: Permeability depends on effective stress when sample is saturated with He, rather than pore pressure, since He is assumed to be none adsorbed gas to coal surface.

Volumetric Method:1. Valves 1,2 open, vacuum the system for half an hour;;2. Close Valve 2, turn off the vacuum pump and then fill the reference cell with gas up to the desired pressure, then close valve 1;;3. Equilibrium when the pressure is constant in the system;;4. Open valve 2 to allow gas flow into the sample cell, then wait for equilib-­rium as mentioned in step 3;; 5. Close valve 2, and fill the reference cell with additional gas to the pres-­sure of interest;;

* Helium is used to measure pore volume before adsorbed gases

Sorption Procedure:Sorption of Gases are measured as a function of pore pressure, effective stress are maintained constant during test. Gas test order: N2,CH4,CO2

Biot, M.A., 1941. General theory of three dimensional consolidation. J. Appl. Phys. 12 (2), 155–164.

Clarkson, C. R.; Bustin, R. M. Binary Gas Adsorption/ Desorption Isotherms: Effect of Moisture and Coal Composition upon Component Selectivity. In Proceedings of the International Coalbed Methane Sympo-sium, University of Alabama, Tuscaloosa, AL, May 3-7, 1999; pp 91-115.

Hagin,P.N., and Zoback, M.D., 2010, Laboratory studies of the compressibility and permeability of low-rank coal samples from the Powder River Basin, Wyoming, USA: American Rock Mechanics Association, 10-170. Presentated at the 44th US Rock Mechanics Symposium and 5th U.S.-Canada Rock Mechanics Sympo-sium, held in Salt Lake City,UT June 27-30, 2010.

Lin, W, Tang,G.Q., and Kovscek, A.R., 2008, Sorption-Induced permeability changes of coal during gas-injection processes. August 2008 SPE reservoir Evaluation&Engineering.

Siemons, N., Busch, A., 2006. Measurement and Interpretation of Supercritical CO2 Sorption on Various Coals: International Journal of Coal Geology, 69 (2007), 229-242.Tang, G-Q., Jessen, K., and A.R. Kovscek, 2005, Laboratory and simulation investigation of enhanced coalbed methane recovery by gas injection, Paper SPE 95947, presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, October 8-12.

Tang, G-Q., K. Jessen, and T. Kovscek,, 2005. Laboratory and simulation investigation of enhanced coalbed methane recovery by gas injection. Paper SPE 95947, In the proceedings of the SPE Annual Technical Con-ference and Exhibition, Dallas, Texas, October 8-12.

White, C. M., Smith, D. H., Jones, K. L., Goodman, A. L., Jikich, S. A., LaCount, R. B., DuBose, S. B., Ozdemir, E., Morsi, B. I. and Schroeder, K. T., 2005, Sequestration of carbon dioxide in coal with enhanced coalbed methane recovery – A review: Energy and Fuels, DOI 10.1021/ef040047w, web release March 22, 2005.

Lin et al (2008)

Hagin and Zoback (2010)