Study on high efficient gas drainage technology of directional fracturing by cutting slots in steep coal seam

Due to the special geological conditions and mining technology of the steeply inclined coal seam, when the horizontal slicing mining method is adopted, a large amount of gas will be released from the lower pressure relief coal body to flow to the working face, causing safety problems. In order to control the threat of gas in the bottom of the fully-mechanized mining face in steep coal seams and reduce the concentration of gas in the bottom of the steep coal seam flowing to the working face, it is proposed to combine water jet slotting with high pressure hydraulic fracturing to form a cutting slot with a directional orientation. A high-efficiency gas drainage technology in the bottom area of the sharply inclined coal seam by combining water jet slotting and high-pressure hydraulic fracturing to form grooves and directional fracturing to increase permeability is proposed. The engineering test was carried out in the south roadway of the east wing of the No. 45 coal seam at the +500 m level in the north area of Wudong Coal Mine of Shenxin Group, and the engineering test was carried out at the level of 40—400 m to the upper layer +525 m. Discussed and analyzed the principle and technological process of high-efficiency gas drainage technology for cutting slots in steeply inclined coal seams, formulated detailed on-site engineering test plans, and a complete set of technology and equipment suitable for high-efficiency gas drainage technology for cutting slots in steeply inclined coal seams has been selected. The results of the study show that: after adopting the cutting slot directional fracturing gas high-efficiency extraction technology to increase the penetration of the gas enriched area at the bottom of the steeply inclined coal seam, the cutting slot directional fracturing borehole can be used for gas drainage under the condition of 20 MPa water injection pressure. The scalar extraction rate is 6.7 times higher than that of ordinary gas drainage boreholes, and the scalar amount of gas extraction from slotted boreholes is 3.0 times higher than that of ordinary gas drainage boreholes; the direct perturbation radius of antireflection is about 6 m，and the radius of influence has reached more than 8 m in the 70 days drainage time. The radius of influence during the mining time has reached more than 8 m. The research results show that the application of this technology to control gas in the bottom coal body of a steeply inclined coal seam is effective, and it effectively guarantees the safe production of the upper slicing working face.