Hydrocarbon Accumulation Evolution of the Cambrian Longwangmiao Formation in the Penglai Gas-Bearing Area, Sichuan Basin

Research on hydrocarbon accumulation in the Cambrian of the Penglai gas-bearing area of paleo-uplift within the central Sichuan Basin remains relatively insufficient. In this study, the hydrocarbon charging history and accumulation evolution model of the Longwangmiao Formation of the Penglai gas-bearing area were established through the integration of petrography, fluid inclusion geochemistry (including microthermometry and Laser Raman spectroscopy), and basin simulation techniques. The findings indicate that the pores in the Longwangmiao reservoirs are extensively filled with solid bitumen. Additionally, multiple generations of diagenetic minerals, such as dolomite, quartz, and pyrite, indicate a complex fluid evolution history. The simulation of the hydrocarbon generation history, combined with homogenization temperatures and salinities of fluid inclusions within diagenetic minerals, reveals that the study area has undergone three crucial hydrocarbon accumulation evolution stages: (1) From the Early Triassic to the Early Jurassic (250–175 Ma), mature oil charged the reservoir, leading to paleo-oil accumulation. (2) From the Late Jurassic to the Late Cretaceous (159–98 Ma), crude oil underwent thermal cracking into gas. (3) From the Late Cretaceous to the present (82–0 Ma), continuous uplift has led to the adjustment of the gas reservoirs. These findings provide critical insights into the gas accumulation patterns and offer guidance for identifying high-potential exploration targets of the paleo-uplift within the central Sichuan Basin.