Study on parameter optimization and permeability enhancement effect of ultra-high pressure hydraulic slotting in coal seams

In response to the core engineering challenge of low gas drainage efficiency and extended extraction cycles commonly encountered in the No.8 low-permeability outburst coal seam of the Wulunshan Coal Mine in Guizhou, this paper focuses on the mechanisms and practical application effects of ultra-high pressure hydraulic slotting for pressure relief and permeability enhancement. Adopting a systematic research approach combining theoretical analysis, COMSOL fluid-solid coupling numerical simulation, and field experiments, the study investigates the controlling effect of slotting spacing on pressure relief and permeability enhancement, optimizes key engineering parameters, and verifies the technical application value. It confirms the significant effectiveness of ultra-high pressure hydraulic slotting technology in expanding the pressure relief range and improving gas drainage efficiency. The results show that: based on the actual geological conditions of the coal seam, numerical simulations are conducted for three slotting spacing scenarios—3 m, 5 m, and 7 m—simulating the evolution of the gas pressure field over a 120-day extraction period. The results indicate that a 3 m spacing enables the earliest connectivity of pressure relief zones and eliminates blind areas of pressure relief. Field experiments are carried out in the 1809 transportation roadway of the mine, comparing three types of boreholes: dense slotting with 3 m spacing, sparse slotting with 7 m spacing, and non-slotting boreholes, using a GF-100 system for construction. The results demonstrate that a single slot created by ultra-high pressure hydraulic slotting achieves an average equivalent pressure relief radius of 1.35 m, significantly increasing the exposed surface area and permeability of the coal mass. Compared to non-slotting boreholes, slotting boreholes maintain a stable gas drainage concentration of 35%-52%, with the pure gas extraction volume increasing by approximately 1.94 times. Moreover, the dense slotting mode with 3 m spacing outperforms the sparse slotting mode with 7 m spacing across all indicators. The optimized ultra-high pressure hydraulic slotting technology can form extensive pressure relief zones and develop fracture networks, significantly enhancing gas drainage efficiency and delaying flow attenuation. This provides a reliable technical approach and practical basis for efficient gas control under similar geological conditions.