Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7206073 | International Journal of Rock Mechanics and Mining Sciences | 2018 | 12 Pages |
Abstract
At present, two types of experiments under stress-controlled conditions were normally conducted to measure coal permeability: constant confining pressure (CCP) tests and constant effective stress (CES) ones. The original rationale of this situation was to assume that the impacts of effective stresses and gas sorption-induced matrix swelling/shrinking on coal permeability could be separated and investigated individually. In this study, we collected coal permeability data measured under both conditions with a purpose to see if this original rationale was appropriate. This goal was achieved through collection of experimental permeability data under the CCP conditions; collection of experimental permeability data under the CES conditions; and comparison of those experimental data with solutions of the poroelastic theory. For CCP tests, the permeability ratios change from reductions (less than 1.0) to enhancements (greater than 1). These changes are bounded by an upper envelope and a lower one. The upper envelope is corresponding to the solution of free-swelling while the lower one zero-swelling. For CES tests, the permeability ratios also change within an upper envelope and a lower one. The upper envelope is equal to 1.0 corresponding to the solution of free-swelling while the lower one zero-swelling. Through these comparisons, we found that permeability data for both types of tests are confined within the poroelastic solutions for two extreme boundary conditions: free-swelling and zero-swelling. These findings suggest that permeability ratios for both constant confining tests and constant effective stress tests are primarily determined by the matrix-fracture interactions, including sorption-induced swelling/shrinking, through transient effective stresses in matrixes and fractures.
Keywords
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geotechnical Engineering and Engineering Geology
Authors
Rui Shi, Jishan Liu, Mingyao Wei, Derek Elsworth, Xiaoming Wang,