Study on gas drainage technology with high level borehole in cont iguous soft coal seams group

In order to solve the poor gas drainage effect of the high level borehole and the gas over limiat the top corner of the coal mining face and other problems in the high stress and contiguous softcoal seams group,a track inclinometer was applied to measure the borehole track.ln combination with the analysis on the parameter design of the site high level borehole,the siteconstruction and gas drainage effect the problemsexisted in the gas drainage technology of the high level borehole were obtained.The cause to make the poor gas drainage effect of the high leveborehole was analyzed.Based on the circumstances a gas drainage optirmized method of the high level borehole was provided. The results showed that the causes to make the poor gas drainage effect of the high level borehole would be the borehole highly deviated from the designed trackand the borehole seam section blocked.The gas drainage designed could be optimized with the control of the drling speed,reductionof the drlng length ,the borehole diameter increased,borehole reamed at the seam section and screen tube. In comparison the gas drainage efect of the high level borehole before and after the optimization,the daily drainage pure volume in average was highly upgraded by three times afer the optimzation and the optimized gas drainage effect was obvious.