Mechanisms of Stress, Temperature, and Gas Pressure on Gas Transport in Coal: An Apparent Diffusion Coefficient-Based Study

As mining operations get deeper, the evolving dynamics of stress, temperature, and gas pressure significantly influence gas transport within coal seams. It is necessary to assess the impact of dynamic changes in environmental conditions on gas transport to promote the development of coalbed methane and coal mine gas extraction technology. This study involves conducting methane desorption experiments under varied stress, gas pressure, and temperature conditions and calculating the apparent diffusion coefficient, considering the seepage effect based on the theoretical models and the observed apparent transport coefficient. The results show that gas transport transitions from diffusion-dominated to seepage-dominated processes as stress exceeds the critical value, with the apparent diffusion coefficient exhibiting an exponential decline. Elevated temperatures enhance gas transport by increasing molecular energy, resulting in an exponential diffusion coefficient rise, as Arrhenius’s formula describes. While the apparent diffusion coefficient increases linearly with gas pressure, the overall impact is less pronounced than the temperature and stress, as it depends on coal properties and competing mechanisms. Furthermore, a comprehensive formula was derived to calculate the apparent diffusion coefficient under varying environmental conditions, integrating the effects of the temperature, stress, and gas pressure. These findings provide a macroscopic understanding of gas transport mechanisms and offer practical parameters for optimizing coalbed methane extraction and mitigating gas hazards.