Western Sichuan The Baima Temple - Qiongxi, - Pingluoba Areas Would Be Sec Gas Reservoir Geochemical Studies

The southern part of the West Sichuan Depression is one of the major gas-producing provinces in Sichuan Basin. There previously existed several different opinions about the accumulation of the gas. In order to get a better understanding of its gas accumulation, the research was carried out in this paper in the case of the migration and accumulation of the gas from the T₃X² section in Pingluoba, Qiongxi and Baimamiao gas fields. First, based on oil-gas geochemical analysis results, and combined with the geological background of the study area, the source, maturity and genetic type of the gas from the T₃X² section was studied through the characteristics of natural gas components, carbon isotope ratio and biomarkers in the reservoir bitumen from the corresponding gas-producing section. Second, directed by the theory of petroleum system, based on the correct gas-source correlation and combined with the research on the structure evolution history, the reservoir pore evolution history and the source rock thermal evolution history, the gas reservoir forming process was expounded from dynamic view, and the charging time of the gas was inferred.The gases from the T₃X² section in west Sichuan are dry(gas dry index> 0.97), the methane carbon isotope ratio is less positive, the ethane carbon isotope ratio is more positive(>-28 %o),and the nitrogen content is lower. Combined with the research on the bitumen reservoir, it was found that the gases belong mainly to the oil-cracked gas of the oil (including wet gas and the condensate) coming from the T₃X¹ section source rock and part of the T₃X³ section source rock. But a few kerogen-cracked gas from the indigenous kerogen was accumulated at the same time.The T₃X¹ section source rock in the deeply-buried part of west Sichuan depression is immature and lower mature at the end of the Triassic, is mature during the late middle-Jurassic, is high mature or postmature at the end of Jurassic. But the T₃X¹ section source rock in the tectonic high part of west Sichuan depression is immature and lower mature at the end of the late Triassic, is mature at the end of Jurassic and is high mature at the end of early Cretaceous. The T3X section source rock in the deeply-buried part of the west Sichuan depression is mature at the end of the Jurassic, is high mature at the end of early Cretaceous. But the T₃X³ section source rock in the tectonic high part of the west Sichuan depression was immature and lower mature at the end of the Jurassic, was mature at the end of early Cretaceous, and is high mature at present.The results from the research on the hydrocarbon source rock thermal evolution history, the biomarker of the reservoir bitumen, the analysis of the fluorescent thin section and the inclusion study show that there are three periods of oil-gas charges, which took place during late Indo-Chinese epoch, early and middle Yanshan epoch and late Yanshan to Himalayan...