Hydrocarbon Kitchen Evolution of the Lower Cambrian Qiongzhusi Formation in the Sichuan Basin and Its Enlightenment to Hydrocarbon Accumulation

The research on the hydrocarbon kitchen evolution of the Lower Cambrian Qiongzhusi Formation can provide important sustain for natural gas accumulation dynamics and exploration direction of the Sinian-Cambrian. Based on thermal history of the Sichuan Basin, the maturity and hydrocarbon generation histories of source rocks of the Qiongzhusi Formation were reproduced, the hydrocarbon kitchen evolution regularity was revealed, the coupling relationship between hydrocarbon generation processes, pale structure and large-scale reservoir formation was established, and the favorable zones of natural gas development in the Sinian-Cambrian were pointed out. The results show that the source rocks of the Qiongzhusi Formation experienced three stages of oil generation, including the Late Caledonian Movement Cycle, the Middle to Late Hercynian Movement Cycle and the Late Indosinian Movement Cycle to Early Yanshanian Movement Cycle; and four stages of gas generation, including the Late Caledonian Movement Cycle, the Middle to Late Hercynian Movement Cycle, the Late Hercynian Movement Cycle to Middle Indosinian Movement Cycle and the Middle Indosinian Movement Cycle to Early Yanshanian Movement Cycle. During the Late Caledonian Movement Cycle, two hydrocarbon kitchens were developed in northern and southern to southwestern Sichuan Basin, respectively, and the latter was the main hydrocarbon generation center; During the Late Caledonian Movement Cycle to the Late Hercynian Movement Cycle, hydrocarbon kitchen in northern Sichuan Basin migrated westward and was the main hydrocarbon generation center. The hydrocarbon generation intensity of hydrocarbon kitchen in southern to southwestern Sichuan Basin increased slightly and the kitchen did not migrate. During the Late Hercynian Movement Cycle to the Late Yanshanian Movement Cycle, a new hydrocarbon kitchen was developed in northwestern to central Sichuan Basin, which had large hydrocarbon intensity and wide area, and this stage was the most important hydrocarbon generation stage. The Sinian-Cambrian natural gas reservoirs were mainly formed by secondary cracking of crude oil. The space-time coupling of massive hydrocarbon generation, high-quality reservoirs in the platform margin and the high tectonic belt have laid a solid foundation for the large-scale accumulation. This research can provide basic parameters for gas exploration and exploitation. For the next exploration of the natural gas of the Sinian-Cambrian system, the high-quality reservoirs in the margin belt of the north central trough should be considered, and the shale gas exploration should be carried out at the positions where the three source rock kitchens are developed.