Numerical simulation on the gas drainage effect of hydraulic jet slotting for pressure relief

To elucidate the mechanism of pressure relief and permeability enhancement in low-permeability coal seams through hydraulic jet slotting, a fluid-solid coupling model for coal seam gas was established. This model incorporates the desorption-diffusion effect, Klinkenberg effect, coal skeleton compression effect, and matrix shrinkage effect. Numerical simulations were conducted using COMSOL software to analyze the optimal interlayer spacing between two slots created in a single borehole, the extent and degree of coal seam pressure relief, and the optimal borehole spacing for gas drainage under hydraulic jet slotting. The results indicate that the optimal interlayer spacing between two slots in a single borehole is from 2.0 m to 2.5 m. The optimal borehole spacing for gas drainage following the application of hydraulic jet slotting for pressure relief and permeability enhancement is approximately 10.0 m. Furthermore, the effectiveness of hydraulic jet slotting in relieving pressure and enhancing permeability is significantly superior to that of hydraulic flushing, with the gas drainage influence radius reaching approximately 5.5 m after 30 days of extraction. These findings provide theoretical guidance for the field application of hydraulic jet slotting as a pressure relief and permeability enhancement measure.