Application of three-dimensional numerical simulation for law of gas drainage through high-level boreholes in lower protective coal seam

Aiming at inferring the drainage effects of boreholes at different horizons under low protective coal seam, the 3D stope model including three kinds of boreholes was established and FLUENT was used to solve seepage and diffusion equation for gaining methane distribution of "Y" ventilation face in space and the drainage effects of boreholes at different position was compared. The results showed that the gas concentration was the lowest near two intake airways and increased along the depth of goaf. Besides, gas tended to float upward on the whol, and a lot of gas of high concentration was accumulated in the upper of the entry at the back of face. Finally, around high level crossing hole which had better drainage effects and large control scope, the gas concentration decreased evidently. Through the stereoscopic drainage with all drill holes, the gas-riched area above goaf became smaller, and the effect of gas redistribution was obvious. The research conclusion accords with monitoring record in site, hence for the working face which has similar near-distance low protective coal seam, the high level hole should be considered as main drainage pattern.