Impact of Air Leakage on Three-Dimensional Gas Distribution in a Longwall Goaf: A Computational Fluid Dynamics Study of High-Level Drainage Roadways

Gas extraction through high-level drainage roadways stands as a critical technology for preventing and controlling coal mine gas disasters. However, significant variations in coal seam thickness or improper layout of these roadways can frequently lead to air leakage problems due to the connectivity of coal-rock fractures, compromising their effectiveness. This study established a three-dimensional numerical model based on Fluent to systematically compare the characteristics of gas distribution within the goaf and the patterns of gas accumulation at the upper corner of the working face under both normal extraction and air leakage conditions in the high-level drainage roadway. The results demonstrate that under different working conditions, the gas distribution in the goaf exhibits a gradient evolution characteristic, progressing from the intake side to the return side and from the bottom to the top, and the gas mass fraction follows a trend of initial increase followed by stabilization. The maximum gas mass fractions in the goaf under normal extraction and air leakage conditions of the high drainage roadway are 2.01 × 10 − 2 and 2.928 × 10 − 2 , respectively. Air leakage significantly reduces the extraction efficiency and gas interception function of the high-level drainage roadway. Specifically, it manifests as a 6.82% expansion of the effective gas distribution range within the goaf, a 45.77% increase in the peak gas mass fraction, and a 58.25% rise in the gas mass fraction at the upper corner. In response to the air leakage issue, a collaborative control strategy integrating supplemental extraction and grouting sealing is proposed. This research reveals the “short-circuit effect” of air leakage in the high-level drainage roadway on gas migration within the stope and the mechanism behind the attenuation of extraction efficiency, providing theoretical support and technical guidance for air leakage prevention, control, and disaster management in similar mines.