Analysis of fault orientation and gas migration characteristics in front of coal mining face: Implications for coal-gas outbursts

Abstract

Coal in a natural geological mass is typically heterogeneous, potentially containing widely distributed faults that affect gas migration and are closely associated with the occurrence of coal-gas outbursts. In this study, the permeabilities of intact and heterogeneous coals during the mining process were described using a dual-porosity model and modified transversely isotropic permeability model, respectively. Numerical simulations based on these models revealed a high gas pressure gradient in front of the working face largely owing to the blocking effect of a low-permeability zone along the fault that led to the formation of a high-pressure gas zone; field measurements confirmed that the gas content in this zone was 2–3 times that in ordinary coal. When close to the fault, a considerable quantity of gas was observed within the working face, then the gas emission increased by 2.4 times once the low-permeability zone along the fault was obliterated. Finally, the proposed model was employed to explain how concurrent increases in shear stress and gas pressure affect the stability of a fault and promote coal-gas outbursts. The proposed model can be applied to conduct theoretical assessments informing measures to prevent gas-related dynamic disasters in coal mines.