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

Abstract

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.