Effect of Tectonic Deformation on the Pore System and Methane Adsorption of Anthracite Coal

Tectonic deformation significantly alters the physical structure of coals, holding great importance to the coal mining industry and coalbed methane. In this study, eight anthracite coal samples with varying degrees of deformation were collected to investigate the effects of tectonic deformation on the pore system and CH₄ adsorption of anthracite coals. In addition, low-temperature gas adsorption (N₂ and CO₂), Raman spectroscopy, and CH₄ isothermal experiments were performed. The results revealed that coal samples with higher degrees of deformation exhibited larger ratios of D-band intensity to G-band intensity (I_D/I_G), indicating increased molecular defects induced by tectonic deformation. As the deformation degree of the coal samples increased, the mesopore volume increased from 0.00044 cm³/g (primary coal) to 0.0019 cm³/g (scaly coal). Conversely, the micropore volume tended to decrease with the increasing deformation degree of the coal samples. Moreover, the impact of deformation degree on the CH₄ adsorption capacity of anthracite coals was complex. With the deformation degree increasing, the Langmuir volume initially decreased from 32.0 to 24.55 cm³/g and then rose to 30.14 cm³/g. This complexity arose from the differential effects of tectonic deformation on various pore types, where micropores and mesopores collectively determined the CH₄ adsorption capacity of anthracite coals. This study analyzed the influence of tectonic deformation on the pore structure and CH₄ adsorption capacity at the molecular level, providing valuable insights for evaluating the in situ CH₄ content in anthracite coal seams.