Pore structure evolution of tar-rich coal with temperature-pressure controlled simulation experiments

Tar-rich coal, with a tar yield of 7–12%, has significant potential for hydrocarbon resources. In this study, typical tar-rich coal samples from Daliuta mining area were selected as the research object to conduct temperature–pressure controlled simulation experiments that simulated stratigraphic conditions. The pore characteristics of the tar-rich coal during coal metamorphism were studied, and the pore evolution law of the tar-rich coal was revealed. The findings demonstrate that this experiment successfully simulates all coal ranks, from low coal rank to high coal rank. Tar-rich coals contain pores of five different genetic types. Gas pores and fissures exhibit a tendency toward growth, while cellular pores are gradually broken and collapsed by compaction, showing a tendency to reduce pores. Mold pores and intergranular pores remain basically unchanged. According to the quantitative analysis of pore structure, each pore has a different evolutionary pattern. Macropores are the primary source of pore volume, micropores are the most active pore component in evolution, and mesopores exhibit a diminishing and then growing "U" shape characteristic. Three phases of tar-rich coal pore evolution—Ro, max < 0.9%, Ro, max = 0.9–3%, and Ro, max > 3%—can be distinguished, and there is a strong correlation between these stages and the coalification jumps.