Geochemistry and Reservoir Characteristics of Jurassic Lacustrine Shale in the Sichuan Basin: Insights from Paleoenvironmental Constraints on Pore Structure

Pore structure directly affects the occurrence and migration of shale hydrocarbon, and the lack of research on the mechanism of the pore structure is an important reason for the hindrance of shale hydrocarbon exploration. By analysing the geochemistry and reservoir characteristics of Jurassic lacustrine shales in Sichuan Basin, this study recovers their paleoenvironments and further discusses paleoenvironmental constraints on pore structure. The results show that the Lower Jurassic lacustrine shales in the Sichuan Basin are in a warm and humid semi-anoxic to anoxic lake environment with high productivity, a strong stagnant environment, and a rapid sedimentation rate, with water depths ranging from about 11.54–55.22 m, and a mixture of type II/III kerogen is developed. In terms of reservoir characteristics, they are dominated by open-slit pores, and the pores are relatively complex. The percentage of mesopores is the highest, while the percentage of macropores is the lowest. Further analysis shows that paleoclimate controls the overall pore complexity and surface relaxation of shales by influencing the weathering rate of mother rocks. Paleoredox conditions control the proportion and complexity of shale pores by influencing TOC content. The research results will provide theoretical basis for improving the exploration efficiency of lacustrine shale resources and expanding exploration target areas.