ABSTRACT:

Although coal-gas interactions have been comprehensively investigated, majority of these studies usually assume that these interactions are under conditions of invariant total stress where effective stresses scale inversely with applied pore pressures and under the assumption of equal gas sorption effect on both matrix and fracture in coal. Permeability models with such assumptions fail to explain results from stress-controlled laboratory tests and are limited in their ability to explain and match in situ data. Through our persistent efforts of almost a decade, we have removed all of these constrained conditions, proposed the local impact of coal-gas interactions on permeability, and developed new relations between coal porosity and volumetric strains under conditions of variable stress. The cubic relation between porosity and permeability is then introduced to relate coal storage capability (porosity) to coal transport characteristics (permeability) also under variable stress conditions. We implement these two relations into a sequence of finite element models to represent the geomechanics of coal-gas interactions including single through dual poroelastic models. These models couple the transport and sorption of a compressible fluid within a deformable medium where the effects of deformation are rigorously accommodated. This paper reports our novel framework on geomechanics of coal-gas interactions.

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