Permeability evolution of gas-infiltrated coal under varied stress paths

Ghazal Izadi, Shugang Wang, Derek Elsworth, Jishan Liu, Yu Wu, Denis Pone

Research output: Contribution to conferencePaper

2 Citations (Scopus)

Abstract

We explore the conundrum of how permeability of coal decreases with swelling-induced sorption of a sorbing gas, such as CO2. We show that for free swelling of an unconstrained homogeneous medium where free swelling scales with gas pressure then porosity must increase as pressure increases. The volume change is in the same sense as volume changes driven by effective stresses and hence permeability must increase with swelling. An alternative model is one where voids within a linear solid are surrounded by a damage zone. In the damage zone the Langmuir swelling coefficient decreases outwards from the wall and the modulus increases outwards from the wall. In each case this is presumed to result from micro-fracturing-induced damage occurring during formation of the cleats. We use this model to explore anticipated changes in porosity and permeability that accompany gas sorption under conditions of constant applied stress and for increments of applied gas pressure. This model replicates all important aspects of the observed evolution of permeability with pressure. As gas pressure is increased, permeability initially reduces as the material in the wall swells and this swelling is constrained by the far-field modulus. As the peak Langmuir strain is approached, the decrease in permeability halts and permeability increases linearly with pressure. The rate of permeability loss is controlled by crack geometry, the Langmuir swelling coefficient and the void "stiffness" and the rate of permeability increase is controlled by crack geometry and void "stiffness" alone. Correspondingly, this represents a mechanistically plausible model for the evolution of permeability in swelling materials.

Original languageEnglish (US)
StatePublished - Dec 1 2010
Event44th US Rock Mechanics Symposium and the 5th US/Canada Rock Mechanics Symposium - Salt Lake City, UT, United States
Duration: Jun 27 2010Jun 30 2010

Other

Other44th US Rock Mechanics Symposium and the 5th US/Canada Rock Mechanics Symposium
CountryUnited States
CitySalt Lake City, UT
Period6/27/106/30/10

Fingerprint

Coal gas
Swelling
swelling
permeability
coal
gas
Gases
void
Sorption
volume change
Porosity
Stiffness
damage
stiffness
Cracks
crack
sorption
porosity
Geometry
geometry

All Science Journal Classification (ASJC) codes

  • Geology
  • Geotechnical Engineering and Engineering Geology

Cite this

Izadi, G., Wang, S., Elsworth, D., Liu, J., Wu, Y., & Pone, D. (2010). Permeability evolution of gas-infiltrated coal under varied stress paths. Paper presented at 44th US Rock Mechanics Symposium and the 5th US/Canada Rock Mechanics Symposium, Salt Lake City, UT, United States.
Izadi, Ghazal ; Wang, Shugang ; Elsworth, Derek ; Liu, Jishan ; Wu, Yu ; Pone, Denis. / Permeability evolution of gas-infiltrated coal under varied stress paths. Paper presented at 44th US Rock Mechanics Symposium and the 5th US/Canada Rock Mechanics Symposium, Salt Lake City, UT, United States.
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Izadi, G, Wang, S, Elsworth, D, Liu, J, Wu, Y & Pone, D 2010, 'Permeability evolution of gas-infiltrated coal under varied stress paths', Paper presented at 44th US Rock Mechanics Symposium and the 5th US/Canada Rock Mechanics Symposium, Salt Lake City, UT, United States, 6/27/10 - 6/30/10.

Permeability evolution of gas-infiltrated coal under varied stress paths. / Izadi, Ghazal; Wang, Shugang; Elsworth, Derek; Liu, Jishan; Wu, Yu; Pone, Denis.

2010. Paper presented at 44th US Rock Mechanics Symposium and the 5th US/Canada Rock Mechanics Symposium, Salt Lake City, UT, United States.

Research output: Contribution to conferencePaper

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T1 - Permeability evolution of gas-infiltrated coal under varied stress paths

AU - Izadi, Ghazal

AU - Wang, Shugang

AU - Elsworth, Derek

AU - Liu, Jishan

AU - Wu, Yu

AU - Pone, Denis

PY - 2010/12/1

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N2 - We explore the conundrum of how permeability of coal decreases with swelling-induced sorption of a sorbing gas, such as CO2. We show that for free swelling of an unconstrained homogeneous medium where free swelling scales with gas pressure then porosity must increase as pressure increases. The volume change is in the same sense as volume changes driven by effective stresses and hence permeability must increase with swelling. An alternative model is one where voids within a linear solid are surrounded by a damage zone. In the damage zone the Langmuir swelling coefficient decreases outwards from the wall and the modulus increases outwards from the wall. In each case this is presumed to result from micro-fracturing-induced damage occurring during formation of the cleats. We use this model to explore anticipated changes in porosity and permeability that accompany gas sorption under conditions of constant applied stress and for increments of applied gas pressure. This model replicates all important aspects of the observed evolution of permeability with pressure. As gas pressure is increased, permeability initially reduces as the material in the wall swells and this swelling is constrained by the far-field modulus. As the peak Langmuir strain is approached, the decrease in permeability halts and permeability increases linearly with pressure. The rate of permeability loss is controlled by crack geometry, the Langmuir swelling coefficient and the void "stiffness" and the rate of permeability increase is controlled by crack geometry and void "stiffness" alone. Correspondingly, this represents a mechanistically plausible model for the evolution of permeability in swelling materials.

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Izadi G, Wang S, Elsworth D, Liu J, Wu Y, Pone D. Permeability evolution of gas-infiltrated coal under varied stress paths. 2010. Paper presented at 44th US Rock Mechanics Symposium and the 5th US/Canada Rock Mechanics Symposium, Salt Lake City, UT, United States.