Dual poroelastic response of a coal seam to CO2 injection |
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| Authors: | Yu Wu Jishan Liu Derek Elsworth Zhongwei Chen Luke Connell Zhejun Pan |
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| Institution: | 1. State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou, Jiangsu, 221008, China;2. School of Mechanical Engineering, The University of Western Australia, WA 6009, Australia;3. Department of Energy and Mineral Engineering, Penn State University, USA;4. CSIRO Petroleum Resources, Private Bag 10, Clayton South, Victoria 3169, Australia;1. School of Mechanical and Chemical Engineering, The University of Western Australia, 35 Stirling Highway, WA 6009, Australia;2. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Hubei 430071, China;3. CSIRO Energy Flagship, Private Bag 10, Clayton South 3169, Australia;1. College of Petroleum Engineering, China University of Petroleum (Beijing), 18 Fuxue Road, Changping, Beijing 102200, China;2. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Hubei 430071, China;3. School of Mechanical and Chemical Engineering, The University of Western Australia, 35 Stirling Highway, WA 6009, Australia;4. IRC for Unconventional Geomechanics, Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang 110819, China;5. CSIRO Energy, Private Bag 10, Clayton South 3169, Australia;6. School of Mechanical and Mining Engineering, The University of Queensland, QLD 4072, Australia;7. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, 18 Fuxue Road, Changping, Beijing 102249, China;1. RWTH-Aachen University, Institute of Geology and Geochemistry of Petroleum and Coal, Lochnerstr. 4-20, D-52056 Aachen, Germany;2. Stanford University, Department of Geophysics, 397 Panama Mall, Stanford, CA 94305, USA;3. University of Calgary, Department of Geoscience, 2500 University Dr. NW, Calgary, Alberta, Canada;1. College of Mining Engineering, Liaoning Technical University, Fuxin, Liaoning 123000, China;2. State Key Laboratory for GeoMechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou, Jiangsu 221116, China;3. State Key Laboratory of Coal Resources and Safe Mining, China University of Mining & Technology, Xuzhou, Jiangsu 221116, China;1. Key Laboratory of Coal Methane and Fire Control, Ministry of Education, China University of Mining & Technology, Xuzhou, China;2. National Engineering Research Center of Coal Gas Control, China University of Mining & Technology, Xuzhou, China;3. Faculty of Safety Engineering, China University of Mining & Technology, Xuzhou, China |
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| Abstract: | Although the influence of gas sorption-induced coal deformation on porosity and permeability has been widely recognized, prior studies are all under conditions of no change in overburden stress and effective stress-absent where effective stresses scale inversely with applied pore pressures. Here we extend formalism to couple the transport and sorption of a compressible fluid within a dual-porosity medium where the effects of deformation are rigorously accommodated. This relaxes the prior assumption that total stresses remain constant and allows exploration of the full range of mechanical boundary conditions from invariant stress to restrained displacement. Evolution laws for permeability and related porosity are defined at the micro-scale and applied to both matrix and an assumed orthogonal, regular and continuous fracture system. Permeability and porosity respond to changes in effective stress where sorption-induced strains may build total stresses and elevate effective stresses. Gas accumulation occurs in both free- and adsorbed-phases and due to effective grain and skeletal compressibilities. A finite element model is applied to quantify the net change in permeability, the gas flow, and the resultant deformation in a prototypical coal seam under in situ stresses. Results illustrate how the CO2 injectivity is controlled both by the competition between the effective stress and the gas transport induced volume change within the matrix system and by the dynamic interaction between the matrix system and the fracture system. For typical parameters, initial injection-related increases in permeability due to reduced effective stresses may endure for days to years but are ultimately countered by long-term reductions in permeability which may decline by an order of magnitude. Models suggest the crucial role of stresses and the dynamic interaction between matrix and fractures in correctly conditioning the observed response. |
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