Research on effective drainage radius and rational borehole spacing of parallel boreholes

In order to determine rational borehole spacing of parallel boreholes for gas drainage, a fluid-solid coupling model of gas drainage was established by deducing gas migration equation of coal seam, deformation equation of coal and rock, and coupling equation of seepage field and stress field. According to actual geological conditions of 21219 working face in a mine, variation law of gas pressure and effective drainage radius under influence of drainage superposition effect between parallel boreholes were numerically simulated by COMSOL Multiphysics software, and rational borehole spacing was obtained by combining with effective drainage radius of borehole. The numerical simulation results show that gas pressure of coal body after drainage increases with the increase of borehole spacing. As the distance between coal body and borehole decreases, gas pressure of coal body decreases slowly at first and then decreases rapidly. With the increase of drainage time, gas pressure decreases continuously and effective drainage radius increases. The field application results verify rationality of borehole spacing arrangement.