Stress-damage-flow coupling model and its application to pressure relief coal bed methane in deep coal seam

Long-distance pressure relief gas drainage technology has recently been applied in mining areas with multiple coal seams of low permeability in China. This study briefly described a coupled stress–damage–flow model, which combined the evolution of stress, damage, and gas permeability with the deformation of coal and rock. The coupled model was then used to investigate the deformation and fracture characteristics of overburden strata, the evolution of gas permeability and gas flow in target coal seams. The effectiveness of long-distance pressure relief gas drainage was evaluated on the basis of the calculated results from a dynamic modelling of extraction of protective coal seam at great depths. The numerical results revealed that the stress was remarkably relieved in the target coal seam above 67 m away from the coal seam being mined. Moreover, the range of stress relief extended above 70 m and the gas permeability increased by more than 2000 times. The modelled results reasonably well agreed with the field results observed in the PANYI coal mine. It was concluded that the long-distance pressure relief gas drainage technology could effectively improve the safety and productivity in underground coal mines, especially in mining areas with multiple coal seams of low permeability.