Coal source rock conditions and hydrocarbon generation model of Pinghu Formation in Xihu Depression, East China Sea Basin

Xihu Depression is the most important coal-forming oil and gas depression in the offshore of China. In recent years, oil and gas exploration has confirmed that the Pinghu Formation coal-series source rocks provide abundant oil and gas resources for Xihu Depression. Different from the Mesozoic coal-forming oil and gas basins in the Terrestrial, the offshore Cenozoic transitional phase of the Cenozoic sea-continental coal source rocks is unique in terms of parent material source, hydrocarbon generation conditions and evolution characteristics. Studies have shown that the source rocks of Pinghu Formation coal-bearing source are rich in tricyclic diiso-isoaspam, beta-flatane and pentacyclic triterpenoids, indicating conifers, ferns and angiosperms. Coal source rock and carbonaceous mudstones are rich in resin, high I_H, Ⅱ₁-Ⅱ₂ type kerogen, and wide-spread distribution characteristics; coal source rocks are rich in tricyclic diterpene iso-seapine, tetracyclic diterpenoid β-phytoplantans and pentacyclic triterpenoids orienes, indicating the source of multi-vegetative parent material of gymnosperms, ferns, and angiosperms; differences in organic matter composition, "internal heat and external cold" geothermal differences in sediment deposition velocity caused significant differences in the evolution of coal and mudstones in different tectonic zones. This difference determines that the coal-derived oil and gas resources have a distribution pattern of "simultaneous oil and gas and east-west oil", and the hydrocarbon-forming evolution of source rocks shows a pattern of "favorable oil production in the early stage and continued gas generation in the late stage".