MULTIPHYSICS OF COAL-GAS INTERACTIONS
The advance of our understanding on coal-gas interactions has changed the way how we treat coalbed methane: from a mining hazard to an unconventional gas resource to a concurrent by-product of CO2 sequestration. When solid coal is removed from or a liquid (supercritical carbon dioxide) is injected into a coal seam, a chain of reactions is induced: gas sorption and flow, coal deformation, porosity change, permeability modification, and so on. In this lecture, we define this chain of reactions as coupled multiphysics. The term coupled multiphysics implies that one physical process affects the initiation and progress of another. The individual processes, in the absence of full consideration of cross couplings, form the basis of very well-known disciplines such as elasticity, hydrology and heat transfer. Therefore, the inclusion of cross couplings is the key to mathematically formulate the coupled multiphysics of coal-gas interactions. Although coal-gas interactions have been comprehensively investigated, all of these prior studies focus on one or more individual processes. They usually assume that these interactions are under conditions of invariant total stress where effective stresses scale inversely with applied pore pressures. Here we started with a new cross coupling relation between coal porosity and four (mechanical, hydrological, chemical and thermal) volumetric strains under variable stress conditions. A cubic relation between porosity and permeability is then introduced to relate coal storage capability (changing porosity) to coal transport property (changing permeability) also under variable stress conditions. These two relations (porosity model and permeability model) have been the key cross couplings that couple the multiphysics of coal-gas interactions. We implemented these two relations into a series of finite element models for the coupled multiphysics of coal-gas interactions from single poroelastic model to dual poroelastic model. These models couple the transport and sorption of a compressible fluid within a deformable 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. We applied these models to investigate the injectivity of CO2 under different in situ conditions, and reported the results in this lecture.
JI-SHAN LIU ZHONG-WEI CHEN YU WU DEREK ELSWORTH
School of Mechanical Engineering, The University of Western Australia, WA, 6009, Australia Department of Energy and Mineral Engineering, The Pennsylvania State University, 110 Hosier Building
国际会议
The 7th International Symposium on Rockburst and Seismicity in Mines(2009年第七届国际岩爆与微振动性学术研讨会)
大连
英文
17-32
2009-08-21（万方平台首次上网日期，不代表论文的发表时间）