Identification and prevention of gas source in goaf: Stable carbon hydrogen isotope tracer method and numerical simulation of gas flow field.

This article focuses on identifying and controlling gas sources in the goaf—the mined-out area behind the working face—in the 28 118 fully mechanized mining face of the Tunlan coal mine in Shanxi Province, China. Using stable carbon and hydrogen isotope analysis of desorption gas from multiple coal seams, the study quantitatively determined that the primary gas sources in the goaf and upper corner are the mined 8# coal seam and the lower adjacent 9# coal seam. Numerical simulations with COMSOL Multiphysics optimized large-diameter borehole extraction parameters—20 m spacing, 10 kPa negative pressure, and 550 mm diameter—demonstrating improved gas extraction efficiency compared to traditional buried pipe methods. Field application of combined large-diameter borehole and directional long borehole extraction technologies significantly reduced gas concentrations in the upper corner by 46.77% and decreased the contribution of gas from the lower adjacent seam by over 40%, effectively mitigating gas accumulation risks in the mining face.