Optimization and Application of Drilling Parameters Based on Gas–Solid Coupling Simulation

The layout of directional high-level long boreholes in fracture zones for extracting pressure-relieved gas from goaf is a key technology to address the gas concentration exceedance in upper corners. To solve the gas exceedance issue at Fengtai Mine’s upper corner, this study established a gas–solid coupling model using COMSOL Multiphysics 6.3 based on actual mine parameters. The research investigated the influence patterns of different extraction parameters (negative pressure, borehole diameter, and extraction duration) on coal seam gas pressure and effective extraction radius (critical gas pressure 0.74 MPa). The results demonstrate the following. The effective extraction radius shows positive correlations with extraction negative pressure, borehole diameter, and extraction time while exhibiting a negative correlation with gas pressure. When borehole diameter exceeds 203 mm, extraction negative pressure surpasses 25 kPa, and extraction duration extends beyond 90 days; the effective extraction radius stabilizes, with the gas pressure influence range ceasing to decrease significantly with further parameter increases. Field validation results showed that, during the observation period, both pure gas extraction volume and mixed gas volume exceeded those of high-level drainage galleries. The gas concentrations in both the upper corner and return airflow remained within safe limits, effectively resolving the gas exceedance issue. This achievement not only established an efficient gas control system for the Fengtai Mine but also provides valuable parameter optimization methods and engineering experience for similar coal mines. The implementation has significantly enhanced gas control efficiency and safety production levels in the mining area.