Application on anti-reflection technology of long borehole along coal seam with medium pressure hydraulic slotting

In deep wells gas extraction with high geostress, low gas permeability, and prominent medium hard coal seams, the volume of gas drainage drilling projects is large, the drainage time is long, and gas disasters are frequent. In order to solve these problems, based on the study of the medium pressure hydraulic slotting mechanism, equipment composition and technical process of slotting, the pressure relief and anti-reflection technology for medium pressure hydraulic slotting in long boreholes along coal seams was proposed, and the engineering practice was carried out in No.1 coal seam of 220108 working face in Xinji No.2 Coal Mine. The results show that the medium pressure hydraulic slotting increases the volume of exposed space in coal mass, and the equivalent radius of the slotting can reach 1.25 m to 1.95 m; the initial velocity of gas emission from the slotting increases by 7.3 times, and the attenuation coefficient of gas emission decreases by 73.1%; the drainage concentration of slotting borehole is increased by 1.8 times, and the drainage volume is increased by 1.3 times, so as to achieve continuous high-concentration drainage. Compared with unslotting ordinary boreholes, the extraction radius of drainage for 15 d and 30 d is increased by 34.8% and 32.2%, respectively, which can effectively shorten the time of drainage compliance, reduce the amount of gas control projects, and solve the problem of unbalanced mining replacement, and achieve safe and efficient mining of strong outburst coal seams.