Coal Pores: Methods, Types, and Characteristics

Coal pores are the locations of coalbed methane occurrence and enrichment and the main storage space targeted in CO2 sequestration. The systematic investigation of the coal pore structure and its development is of great significance to provide insights into coalbed methane generation, coal mine gas outburst mechanisms, and coal seam CO2 sequestration. In this study, coal pore testing technologies and methods, pore classification methods, and coal pore structure characteristics and their main control factors were systematically investigated and summarized. The results show that direct test methods, indirect fluid injection test methods, and X-ray and spectroscopic methods have been used for the quantitative characterization of the pore structure. However, each testing method has limitations. Therefore, a comprehensive method for the quantitative characterization of the full-scale pore structure must be developed, especially for the accurate quantitative characterization of closed pores in coal. The in situ measurement of pores in coal is one of the future research trends. Classification methods of pores in coal mainly include the classification of the genetic pore type, pore size, and pore morphology. Metamorphism, tectonic deformation, and macerals are the main internal factors affecting the pore distribution in coal. The effect of tectonic deformation on the macromolecular structure and micro- and ultramicropores of coal must be further studied. In addition, molecular mechanics simulations, molecular dynamics simulations, and quantum chemistry calculations of the dynamic response of the macromolecular structure and micro- and ultramicropores during gas adsorption and desorption must be carried out.