Methane release and energy evolution in coal and its implication for gas outburst

Gas outburst is a common underground geological hazard that poses a serious threat to coal mine safety production. To elucidate the influence of methane release behavior and energy evolution on gas outburst in coal, the microscopic pore parameters and macroscopic methane release law of six coal rank samples were studied by full-scale pore test, Scanning electron microscopy-Pores and Cracks Analysis System analysis and temperature measurement experiments during methane desorption. The results show that with the increase in coal rank, pore complexity, and the chaos of pore direction distribution first decrease and then increase. The pore volume and pore area of low/high-rank samples are relatively large, with well-developed pores, especially micropores, which are prone to gas accumulation and have great potential for outburst. The evolution of methane desorption-diffusion performance with coal rank is corresponding to pore development degree, methane in high rank coal is rapidly transferred at a high diffusion rate. The desorption prediction model related to temperature change can accurately characterize the relationship between temperature variation and desorption amount in the process of methane desorption. With the increase in coal rank, the desorption heat value and gas expansion energy of samples show a U-shaped trend of decreasing first and then increasing. In high-rank coal seams, large methane potential energy accumulates, posing considerable outburst potential and threats. The research findings can provide certain guidance for the prediction and forecasting of gas outburst disasters.