Study on the difference of gas drainage effect between cross-measure borehole and inseam borehole hydraulic punching

With the gradual increase in China's coal mining depth, coal seams exhibit high gas content, high gas pressure, and low permeability, exacerbating the difficulty of gas drainage. Hydraulic punching has become an effective means to improve the efficiency of coal seam gas drainage by relieving pressure and increasing permeability in coal seams. To solve the problem of low permeability and difficult gas drainage in the No. 3 coal seam of Changping Coal Mine, hydraulic punching was implemented in the 5302 floor drainage tunnel and 53 023 tunnel, which were used as the engineering background. First, based on the elastic mechanics strain softening model and the diffusion seepage coal seam gas flow theory model, the evolution equation of coal seam permeability and gas flow equation after hydraulic punching was established, and numerical simulation software was used to analyze the pressure relief and permeability enhancement mechanism and permeability distribution law of hydraulic punching. Then, the field tests of ordinary and hydraulic punching boreholes were conducted to compare the gas drainage effect. The results showed that the effective influence radius of hydraulic punching was 4–5 m, and the influence radius was 5–8 m. The reasonable punching water pressure was 17.51 MPa, and the reasonable punching time was 60 min. The gas drainage concentration of cross-measure borehole hydraulic punching and inseam borehole hydraulic punching was 1.77 and 1.49 times higher than that of ordinary borehole, respectively. From the gas drainage concentration index perspective, the drainage effect of cross-measure borehole hydraulic punching was the best. However, the gas drainage purity was 2.88 and 3.08 times, respectively. From the gas drainage purity index perspective, the drainage effect of inseam borehole hydraulic punching was the best. The coal seam driving efficiency in the area affected by punching increased by 37%. Hydraulic punching can effectively eliminate coal seam outburst hazards, improve coal seam permeability, and ensure the safe and efficient production of mining faces.