Influence of the roadway exposure time on the accuracy of gas content measurements in reconstructed and extended mines

The 100-year global warming potential of methane is 28 times higher than the value of carbon dioxide. Accurate gas content measurement is a precondition of coal mine reconstruction and extension designs for reducing methane emission due to that in these scenarios the stress and gas pressure distributions were unpredictably disturbed by previous mining activities. Longer roadway exposure time induce lower gas content and high measurement error. In this study, a coupling model considering the influence of gas transport, solid mechanics, and permeability evolution was established to predict the gas pressure distribution in coal seams. Based on this model, the influence of the roadway exposure time on the gas pressure distribution in an extended mine, Hulonggou Mine, was numerically studied with the software of COMSOL. The results show that the stress concentration area near the roadways can reduce the rate of gas emission. In addition, the gas pressure relief zone becomes increasingly larger as the emission time increases. For the studied coal seam, the boundary of the gas pressure relief zone is about 25–30 m to the center line after 25 years’ gas emission. At last, actual gas content measurements validated the simulated results. The results can help scholars properly predict the gas content and design the gas drainage plans for coal seams that have been excavated for several years.