Genetic,sources And Transportation And Accumulation Patterns Of Natural Gas In The Maokou And Jialingjiang Formations In Southern Sichuan Basin

The Maokou formation of the middle Permian and the Jialingjiang Formation of the lower Triassic are important productive formations in southern Sichuan,and the source of their gas has been controversial.In this paper,by using the methods of petroleum geology and organic geochemistry of oil and gas,combines organic geochemical analysis and geological background to discuss genetic types and sources of natural gas of Maokou Formation and Jialingjiang Formation,which the main research content include the hydrocarbon source rock evaluation,the natural gas geochemical characteristics and gas source correlation three aspects.Meanwhile,the gas transportation and accumulation mode is established.The following conclusions are drawn:(1)The Maokou and Jialingjiang Formation have many sets of source rocks related to reservoir formation,among which the source rocks of Longmaxi,Longtan and Maokou Formation have the conditions to form large and medium-sized gas reservoirs,while the source rocks of Jialingjiang Formation have certain hydrocarbon generation ability,but they do not have the conditions to generate large quantities of hydrocarbons.(2)The genetic types of natural gas in Maokou formation and the Jialingjiang Formation are similar.They belong to the source rock pyrolysis gas.The natural gas sources of Maokou Formation were different in different structures in Southern Sichuan Basin.The natural gas without the source fault of Longmaxi formation only comes from the source rock of Maokou formation,while the natural gas with the source fault of Longmaxi formation comes from the source rocks of Maokou Formation and Longmaxi Formation of Lower Silurian.The gas sources of the Jialingjiang Formation in different structures are different and in Hejiang-Tanghe area mainly comes from the source rocks of Maokou Forrnation,Longtan Forrnation and Jialingjiang Formation.The natural gas in Zigong and Qijiang area mainly comes from the source rocks of Longtan Forrnation and Jialingjiang Formation.(3)There are two modes of natural gas accumulation in Maokou formation,which are the self-generation and self-accumulation and the dual-source co-storage accumulation.The natural gas migration channels of Maokou formation are fractures and faults.The natural gas in Jialingjiang Formation is a mixed source accumulation model of lower product and upside reservoir.The lower Permian natural gas is transported up the overlying rock by the hydrocarbon source fault,and it accumulates in the carbonate reservoir of Jialingjiang Formation.