Combined Effect of Multiple Slotting Spatial Parameters on Gas Extraction Efficiency: Numerical Analysis and Field Verification

Hydraulic slotting is an effective technology that enhances gas extraction operations and prevents gas disasters in coal mines. Slotting parameters and spatial arrangements substantially affect permeability enhancements. The pressure-release range and effective extraction area under different slotting spatial parameters were obtained by constructing a hydraulic slotting pressure-release permeability and three-dimensional (3D) slotting numerical models. These models quantitatively characterized the influence rules of multiple slotting spatial arrangement parameters on the extraction efficiency at a 3D scale, clarified the interactions of multiple slottings and their combined effects on pressure relief and permeability enhancement, and verified the results using field engineering tests. The results showed that hydraulic slotting significantly alters local stress and strain distributions, creating high-strain and high-stress zones with clear spatial attenuation. The process enhances fracture development, reducing gas pressure from 1 MPa to 0.08 MPa, thereby improving extraction efficiency. Enlarging the slot dimensions from 1.5 to 2.5 m increases the gas pressure-relief efficiency by up to 41% and nearly triples the impact radius. Wider slot spacing (1.5 m to 3.5 m) and additional slots (from one to three) further reduce the borehole gas pressure by 23% to 25%, optimizing hydraulic slotting technology for practical applications.