Parametric Optimization of Gas drainage via Cross-measure boreholes in Floor Strata in a Coal Mine: A Multiphysics Simulation Study

Effective gas drainage in coal mines necessitates the precise optimization of borehole parameters to reduce gas pressure and prevent gas outbursts. However, current drilling designs predominantly rely on field experience rather than site-specific quantitative analysis of geological conditions, leading to limitations in adaptability. This study establishes a COMSOL-based multiphysics coupling model that integrates stress-permeability interactions, gas adsorption-desorption kinetics, and fracture-induced permeability evolution to evaluate the gas drainage performance of cross-measure boreholes in floor strata. Simulation results indicate that directional borehole spacing is the most influential factor: reducing the spacing from ۲۵ m to ۲۰ m significantly increases gas drainage efficiency by ۳۱.۴%, while extending the drainage duration from ۹۰ days to ۲۷۰ days expands the influence radius by more than ۳۵%. In contrast, variations in borehole diameter (۷۵-۱۱۵ mm) and negative pressure (۱۰-۹۰ kPa) exert a negligible impact on gas pressure (with a variation of less than ۵%), reflecting limited sensitivity. The optimal borehole location is determined to be at the lower boundary of the mining-induced fracture zone. A gradient layer analysis further confirms that the perforation depth should match the range of the plastic deformation zone (۱۵-۲۵ m). The proposed parametric optimization strategy provides a quantitative framework for directional drilling design, enabling the matching of borehole layout with the scale of fracture development. These findings contribute to enhancing the accuracy of gas control and the engineering adaptability of gas drainage systems under complex geological conditions.

کلیدواژه ها:

floor strata ، cross-measure boreholes ، borehole parameter optimization ، stress–permeability coupling ، multiphysics simulation