Determination of Rational Pattern Space for Gas Pre-Drainage Borehole in Mining Seam

In order to provide the basis for the design of the gas pre-drainage borehole space in the mining seam,taking the mining seam as the double medium of the porous fractures,in comprehensive consideration of the gas penetration flow and diffusion desorption processing,a gas flow equation was established and the max space between the boreholes to meet the requirements of the pre-drainage time and the seam gas pre-drainage rate was calculated as for the rational pattern space for the gas pre-drainage boreholes in the mining seam.The applied study was conducted on the coal mining face in No.8 seam of Du'er'ping Mine and the results showed that as the space between the boreholes increased,the seam gas pre-drainage rate would be in the reduction tendency at the same time.And within a pre-drainage time of 200 d,under the requirement of the seam gas pre-drainage rate of 30%,the 5 m space between boreholes applied in the coal mining face would be most rational and economic.