A Study On Geochemical Characteristics Of Reservoir Forming Geochronology Of Upper Triassic In Western Sichuan Depression

The west sichuan depression belongs to a typical Superimposed foreland basin. It has experienced complicated tectonic movement since Upper Triassic Xujiahe Formation. Numerous oil and gas pools are widely distributed in this field. Because of specific complicated geological situation and experienced complicated geological changes, bringing up clastic reservoirs the Formation Time,the characteristics of Fluid Evolution and distribution are very complicated,and also determines serious heterogeneity of reservoir distribution in the field.By studying the Characteristics of Upper Triassic,Jurassic and Cretaceous strata rock combination in the west sichuan depression, the clastic rock gas-bearing system in west sichuan depression is divided into three reservoir-forming system, namely the Xiaotangzi and Ma'antang formation—the second and third member of Xujiahe Formation reservoir-forming subsystem;the third—fourth and fifth member of Xujiahe Formation reservoir-forming subsystem;the fifth member of Xujiahe Formation—Jurassic—Cretaceous reservoir-forming subsystem. The fourth member of Xujiahe formation is divided into two reservoir-forming subsystem: that is the third member of Xujiahe Formation—upper and middle sub-member of the fourth member of Xujiahe Formation;middle and lower submember of the fourth member of Xujiahe Formation—the fifth member of Xujiahe Formation.System research on the oil and gas accumulation elements, including study on the characteristics of source rocks in upper Triassic,such as the organic carbon content,chloroform bitumen"A",Kerogen Types,vitrinite reflectance,etc; The organic carbon content of the source rock in Xujiahe formation is very high, organic matter type is dominated by III, with a little II organic matter.the source rock has high maturity, most of which are into high mature stage,and a little of them are into over-mature stage. Study on the characteristics of reservoir porosity evolution in the second and fourth member of Xujiahe Formation,the period of reservoir capability in the second member of Xujiahe Formation are the Xujiahe formation of third early sedimentary period—Terminal of Middle Jurassic and himalayan period; the period of reservoir capability in the fourth member of Xujiahe Formation are the Xujiahe formation of third early sedimentary period—Terminal of early cretaceous and himalayan period. Research on the peak stage of hydrocarbon generation and expulsion,the second member of Xujiahe Formation has two peak stage of hydrocarbon generation and expulsion: the fourth member of Xujiahe Formation and Middle—Late Jurassic; the fourth member of Xujiahe Formation also has two peak stage of hydrocarbon generation and expulsion: the Xujiahe formation of fourth middle sedimentary period—the Xujiahe formation of fourth terminal sedimentary period and Middle—Late Yanshanian.Which are the favorable basis for analysis on reservoir forming geochronology of each reservoir-forming system.Research on the history of generation and expulsion hydrocarbon of source rock, evolution history of reservoir porosity, sealing ability of Caprock, trap characteristics, hydrocarbon inclusionand isotopic dating by using macroscopic and microscopic, qualitative and quantitative, dynamic and static, geological analysis and experimental means combine together. which determine the reservoir forming geochronology of the Xujiahe formation of second and the fourth. The reservoir forming geochronology of the Xujiahe formation of second has three periods:that is the Xujiahe formation of fifth sedimentary period,Terminal of Middle Jurassic—early cretaceous and himalayan period.The reservoir forming geochronology of the Xujiahe formation of fourth also has three periods:that is the Xujiahe formation of fifth sedimentary period, Late Jurassic—Terminal of early cretaceous and himalayan period.