Nanopore Structural Characteristics and Their Impact on Methane Adsorption and Diffusion in Low to Medium Tectonically Deformed Coals: Case Study in the Huaibei Coal Field

Coupled with isothermal adsorption and the Steele potential function, the characteristics of nanopores and their impact on methane adsorption and diffusion in low- to medium-rank tectonically deformed coals (TDCs) were revealed by high-pressure mercury intrusion and low-pressure N2/CO2 gas adsorption. The specific surface area (SSA) of low to medium TDCs is mainly provided by micropores ( 50 nm, 99.68–99.91%). The fractal characteristics of nanopores can be divided into four groups, i.e., D1 (>100 nm), D2 ( 8 nm), and D4 ( D2, indicating that the heterogeneity of seepage pores is stronger than that of adsorption pores. For scaly coals, D2 ≈ D1, demonstrating the close heterogeneity and connectivity in adsorption and seepage pores, which are beneficial for coalbed methane (CBM) desorption and diffusion. However, D2 > D1 for wrinkle and mylonitic coals, indicati...