Impact of methane gas diffusion in coal on elastic modulus and porosity: Modeling and analysis

Energy-consuming countries pay more attention to the recovery and utilization of coalbed methane (CBM) because it is a kind of clean energy with abundant reserves. Methane gas diffusion, a core link affecting the recovery efficiency of CBM, is a thermodynamic process affected by complex factors. Therefore, the study of methane diffusion dynamics is of great significance for the analysis of gas flow evolution and the prediction of CBM production. In this work, a constitutive model of methane-saturated coal is developed from the perspective of non-equilibrium thermodynamics. Several factors that affect methane diffusion are considered in this model, including methane concentration, diffusion pore length, pore resistance, and temperature. To verify the correctness of the model, three typical metamorphic coal samples are selected for the methane diffusion experiment. During the gas diffusion of methane-saturated coal, the time evolution of methane concentration and elastic modulus are tested. Comparing the theoretical results of the model with the experimental data, we find that they are in good agreement. Finally, the effect of model parameters on methane diffusion rate in coal is analyzed, and the evolution of coal elastic modulus and porosity during the methane diffusion process is predicted.