Gas control technology of directional high-level long borehole at upper corner

For problems that normal roof high-level borehole hardly drilled to design position because borehole direction and dip-angle cannot be controlled, and had short effective extraction hole segment, many drainage blind areas, discontinuous drainage and so on, taking upper corner gas control of Wangjialing Coal Mine as research background, a group of directional high-level long borehole and four groups of normal high-level borehole were constructed for gas drainage in return airway of 20103 fully mechanized working face. Gas drainage effect of the two kinds of high-level boreholes were compared and analyzed. The results show that the effective drainage hole section of the directional high-level long borehole is long, the blind area of gas drainage is few, meanwhile, continuous drainage can be achieved. The average gas drainage flow from the directional high-level long borehole is 2.11 m3/min and the maximum value achieves 2.9 m3/min. Compared with normal high-level borehole, the average gas drainage flow from the directional high-level long borehole increases about 2.77 times, the gas drainage rate of working face increases nearly 2 times, and the effect drainage time increases about 3.15 times. The gas volume fraction at upper corner is reduced from more than 1.0% under the condition of only draining gas from normal high-level borehole to less than 0.6% only draining from the directional high-level long borehole, which verifies that the directional high-level long borehole has obvious technical advantages of controlling upper corner gas on working face.