Numerical Test of Gas Pre-drainage with Dense Boreholes in Outburst Coal Seam

The dense borehole pre-drainage technology is a preventive measure for coal and gas outburst.In order to enhance the pre-drainage efficiency and rationally arrange borehole,the solid-gas coupled RFPA2D-GAS numerical test system is applied to study the variation regularity in gas pressure and drainage radius under different factors.These factors include coal seam permeability coefficient,space between boreholes,borehole diameter,gas content coefficient and pre-drainage time.It can be concluded that if large permeability coefficient and large borehole diameter are used with small space between boreholes and small content coefficient in the coal seam,then the lowered range in gas pressure and drainage radius will be large.It is required the shortest pre-drainage time to avoid the outburst danger of coal seam.If the pre-drainage time prolongs,the lowered range in gas pressure and drainage radius increase.An engineering practical experiment is found to approve to this numerical test.