Practice of gas drainage by high-level directional borehole in Qinglong Coal Mine

Aiming at problems of gas drainage by high-level borehole such as too many boreholes, insufficient single borehole depth, uncontrollable borehole trajectory, low gas drainage concentration and discontinuous drainage, in order to effectively prevent and control gas concentration overrunning in upper corner of 21602 mining face in Qinglong Coal Mine, gas drainage was carried out by use of high-level directional borehole technology. Design and construction schemes of high-level directional borehole were introduced, and the best borehole layout parameters were determined through field practice. The results show that high-level directional borehole has the characteristics of high gas drainage concentration, large drainage volume and high drainage rate, and gas drainage effect of high-level directional borehole tends to stabilize first and then decreases with the increase of mining distance. When the final hole of high-level directional borehole is 39 m away from roof and 55 m away from right side of return airway, gas drainage effect is the best with gas drainage volume fraction reaching 30.5%, gas drainage flow reaching 18 m3/min and gas drainage pure volume reaching 2.374 m3/min. Gas volume fraction in upper corner is reduced to the range from 0.2% to 0.4%, which is up to 0.72% before extraction. It effectively solves problem of gas concentration overrunning in upper corner.