Abstract
Coal seam contains a large number of fractures, whose shape and structure of fissures are complicated, and they are the main channels for gas migration. Therefore, the quantitative analysis of the internal relationship between the microstructure and the macroscopic permeability is the key issue to increase the drainage volume. Some investigators discussed the permeability of coal seams based on the fractal theory, but the mechanisms of gas migration under the influence of fissure microstructures and coal deformation are still unclear. Moreover, most of the multi-process coupling analysis in the stage of Coal Bed Methane (CBM) mining was not taken into account. In this paper, the effects of fissure structures on the coal gas drainage rate in multi-field coupling are studied. Aiming at the mechanisms of gas drainage under the joint action of fracture structure, in-situ stress and adsorption deformation, we propose a two-scale multi-field coupling model, which takes into account the influences of micro fracture and pore structure. On this basis, we obtained the pressure evolution rule of coal seam pore system and fissure system and the distribution rule of coal seam displacement with drilling positions. Meanwhile, the effects of coal seam maximum fracture length, maximum pore diameter, the fractal dimension for fractures and fractal dimension for pores on coal seam extraction are discussed.
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