Microscopic Pore Structure Characteristics and Methane Adsorption of Vitrain and Durain

During reservoir evaluation, the microscopic pore structure of low-rank coal is mainly characterized in order to study the coalbed methane diffuse and migration mechanisms and control. The low-rank coals are very different in pore type and size, so it is necessary to use various techniques to describe their pore structure. For vitrain and durain of the Coal Member of the Yan’an Formation from Huanglong Coalfield, their chemical composition and microscopic pore structure characteristics were studied, and the factors of influencing the pore size distribution (PSD) were explored. Obviously, vitrain and durain are different in chemical composition. Vitrain has higher moisture content, volatile yield, and vitrinite group content than durain. Vitrain and durain mainly contain vitrinite and inertinite, respectively. The pore structure characteristics (e.g., pore types and PSD) of vitrain and durain were systematically by mercury intrusion porosimetry (MIP), low-temperature nitrogen adsorption, and carbon dioxide (CO2) adsorption. The vitrain and durain samples with a micropore size of