Research on Combined Perforation and Blasting Technology for Increasing Permeability in Low-Permeability Hard Coal Seams

To address the low efficiency and uncontrollable fracture expansion in gas extraction from low-permeability hard coal seams, a synergistic permeability enhancement technology integrating loose blasting and hydraulic perforation (LBHP) is proposed. Combined with theoretical analysis, ANSYS/COMSOL numerical simulations and field trials, the synergistic mechanism of active prefracturing by loose blasting and hydraulic expansion optimization was revealed, and key process parameters were optimized. The optimal spacing between control holes and blast holes is determined to be 3 m through numerical simulation. Simulation results show that the LBHP technology increases coal seam equivalent permeability by 3.8 times (from 2 × 10 − 17 m 2 to 7.6 × 10 − 17 m 2 ), and the effective gas extraction radius reaches 6.44 m (172% higher than traditional technology) under optimal parameters. Field trial data in Jiulishan Mine verify that, compared with single hydraulic perforation, the LBHP technology improves per-meter coal flushing volume by 14.3%, operation efficiency by 21.4%, methane extraction concentration by 23.4%, and pure methane flow rate by 35.12%. The LBHP technology realizes active control of coal seam fracture network, providing a new technical solution for efficient gas control in deep low-permeability hard coal seams with important engineering application value.