Thermal evolution and hydrocarbon generation histories of black shale in Lower Carboniferous Baizuo Formation, Southern Guizhou Depression

The thermal evolution and hydrocarbon generation histories of the Lower Carboniferous Baizuo Formation in the Southern Guizhou Depression were studied with petroleum geology, geochemical data and petroleum system simulation in order to evaluate the hydrocarbon generation potential of black shale. Results showed that the black shale of the Baizuo Formation has relatively high organic matter abundance and low hydrocarbon potential. The organic matter in the black shale is mainly of type Ⅱ₂, and has reached the high-maturity and over-mature stages. The black shale entered the threshold of hydrocarbon generation during the Middle Carboniferous (about 312 Ma) and the mature stage in the early Triassic (about 238 Ma), and reached the maximum burial depth (about 9 000 m) in the early Jurassic (196 Ma), with a maximum temperature of about 200℃. They reached the oil generation peak in the Middle Permian (291-270 Ma) and the gas generation peak in the Late Triassic (262-208 Ma), respectively. The process of oil cracking to gas during the high thermal evolution provided sufficient methane gas and storage space for shale gas enrichment. However, tectonic uplift and erosion since 196 Ma had a certain destructive influence on shale gas enrichment.