Molecular Simulation Investigation into the Construction of Nanopore Structures in Coal and the Occurrence Mechanism of Gas

Coalbed methane serves as a vital clean energy resource that plays a notable role in mitigating imbalances in the energy supply and demand and improving energy structure optimization. Methane is predominantly confined within the microporous structure of coal, posing challenges for its desorption process. Comprehending the microscale flow mechanisms of methane is essential for optimizing desorption efficiency. Herein, molecular models of the coal micropore structures were developed by using experimental techniques to investigate their adsorption characteristics and the adsorption/diffusion behavior of methane. The findings reveal that most of the coal micropores are smaller than 10 nm, with the highest concentration observed in the 2–4 nm range. The adsorption capacity of the gas decreases with increasing temperature, while it increases with the pressure and the degree of coal metamorphism. Methane adsorbed in the coal matrix pores has a lower propensity for desorption than methane in the coal body pores. Additionally, gas diffusion in pore-free spaces follows a decreasing trend with pressure and the degree of coal metamorphism.