A comprehensive study of multiscale pore structural characteristics in deep-buried coals of different ranks

The pore structure characteristics of coal significantly influence its gas adsorption and desorption capacity, as well as gas migration, playing a crucial role in the development of coalbed methane and the management of gas-related disasters. To investigate the pore distribution characteristics of coal in-depth, pore data for coal samples with varying degrees of metamorphism were obtained using low-pressure nitrogen adsorption (LPGA-N₂), low-pressure CO₂ adsorption (LPGA-CO₂) methods, and mercury intrusion porosimetry (MIP). Multiscale pore size distributions were constructed for three types of coal samples. By combining Scanning Electron Microscopy (SEM) and the Pore-Crack Analysis System (PCAS), which derived SEM images, pore numbers, pore area, heterogeneity coefficient, curvature coefficient, fractal dimension, and porosity data, a quantitative analysis of the multiscale pore distribution characteristics of the three coal samples was conducted. The results indicate that multiscale pore size distribution diagrams are an effective method for studying the multiscale pore characteristics of coal, allowing for quantitative investigation of pore distribution characteristics at different scales. YW coal exhibited the highest micropore content (0.0723 cm³/g), followed by DLT (0.0333 cm³/g) and JG (0.0205 cm³/g). For mesopores, JG had the highest content (0.0182 cm³/g), and for macropores, DLT had the largest volume (0.627 cm³/g). This comprehensive analysis enhances the understanding of coal's multiscale pore structure and its intrinsic link to adsorption properties. This research is significant for further understanding the pore structure characteristics of coal and revealing the intrinsic link between coal pore characteristics and adsorption properties. The findings are crucial for developing more effective gas drainage schemes, improving gas management in coal mines, ensuring safe production, and reducing greenhouse gas emissions.