Study and application of reasonable parameters for hydraulic punching of layer penetration boreholes in Changping Coal Mine

Aiming at the application of hydraulic punching technology in soft, low permeability, and high gas coal seams in Changping Coal Mine, there are problems such as large workload, poor permeability enhancement effect, and the formation of "blank zones" in the pressure relief and permeability enhancement areas caused by workers' blind construction. By using a combination of theoretical analysis, numerical simulation, and on-site practice, the threshold pressure for punching and breaking coal was calculated. The simulation analysis determined the reasonable key parameters for hydraulic punching through layered drilling, providing theoretical support for engineering applications; and the application effect of key parameters was investigated in the 5302 bottom extraction roadway of Changping Coal Mine. The research results show that the threshold value of incident pressure for punching and breaking coal in the No. 3 coal seam of Changping Coal Mine is 4.26 MPa, the reasonable hydraulic punching water pressure is 15 MPa, the punching angle is 60 & DEG;, the diameter of the punching hole is not more than 0.8 m, and the punching time is 120 min; when the punching water pressure is lower than 4.0 MPa, effective coal flushing cannot be achieved. When the water pressure is between 4.0 and 15.0 MPa, the total amount of coal flushing is positively correlated with the punching water pressure; under the determined reasonable parameter punching conditions, the extraction influence radius is 8.9 m, the effective extraction radius is 5 m, and the average pure gas extraction volume is 0.089 m(3)/min. Under this parameter, hydraulic punching technology effectively improves the permeability characteristics of coal seams, which is conducive to long-term gas extraction and has a significant effect on pressure relief and drainage promotion.