Pore structure evolution of low-rank coal in China

Abstract In China, low-rank coalbed methane (CBM) resources are in the early stage of exploration. The evolution of pore structure for these coals around the first coalification jump is incomplete. Here systematic experiments were conducted to analyze the reservoir of low-rank coal (lignite and subbituminous coal) from China's major low-rank basins, thus revealing the pore structure evolution of low-rank coal in China. Scanning electron microscopy (SEM) demonstrates that there are obvious differences in the pore types of different rank coals. Well-developed cell lumina provides a large amount of macropore space in coals with R o o is 2 spectrum shows a series of complex changes from trimodal to bimodal to trimodal and finally to bimodal, indicating that the pore size distribution undergoes continuous changes. With the continuous coalification and physical compaction, the porosity decreases rapidly with vitrinite reflectance increases from 0.42–0.68%, and the adsorption capacity shows an increasing trend with the increase of coal rank under the control of moisture content, pore type, and specific surface area. Understanding the evolution of pore structure in the early stage of coalification will provide a scientific reference and foundation for exploration and development of low-rank CBM.