Hydrocarbon Migration And Accumulation Models Of The Fushan Depression

As an important hydrocarbon-bearing depression in Beibuwan Basin,the Fushan depression is a"small but rich"oil and gas-rich sag,in which Liushagang Formation serves as the primary source and reservoir.The oil and gas distribution in the Fushan depression has the laws of"East gas and west oil","deep gas and shallow oil"and"Central and Eastern enrichment".However,at present,the process of hydrocarbon migration,accumulation and reservoir forming model are not clear,which restricts the selection of exploration direction.Therefore,based on the analysis of the basic petroleum geological characteristics of Fushan depression,this study made geological analysis and numerical simulation of hydrocarbon generation and migration process,carried out a systematic analysis of the process of hydrocarbon migration and accumulation,revealed the main controlling factors and distribution law of oil and gas distribution.The results show that,the abundance and types of organic matter of source rocks in the Fushan depression are not very different,but due to the intrusion of igneous rocks,the maturity of source rocks in the Bailian sub sag is significantly higher than that in other areas.Typical wells in various regions are selected for burial history and thermal history simulation,calibrated with actual vitrinite reflectance（Ro,%）data and simulated data,and the hydrocarbon accumulation periods are analyzed in combination with inclusion homogenization temperature measurement data,burial history and thermal history.It is found that the reservoir forming period of the Bailian and Huangtong sub sag in the Fushan depression is earlier than that of the Huachang sub sag,and the reservoir forming time of the southern slope zone is the latest.The transportation path and fluid potential energy of Fushan depression are studied,and the dominant migration direction of hydrocarbon is analyzed using multi-factor normalization and superposition.The normalized fluid potential distribution shows that the oil and gas in Huangtong sub sag mainly migrates to the Northeast（Yong’an,Huachang）,Southeast（Hongguang）and Southwest（Chaoyang,Meitai）,while the hydrocarbon in Bailian sub sag mainly migrate to the North（northern sea area）,Southeast（Jinfeng）Southwest（Hongguang）and West（Huachang）.It is consistent with the comparison results of carbon component isotopeδ¹³C value,gammacerane index and planting ratio of source rock crude oil.According to the basin simulation and numerical simulation analysis of hydrocarbon migration,oil and gas migrated from the hydrocarbon generation sub sag of Bailian in the East and Huangtong in the west to the sub convex of Huachang and the southern slope zone.Vertically,The oil and gas generated in E₂l₂ migrated to E₂l₁ during fault activity.E₂l₃ is deeply buried and enters the gas generation stage.However,the extremely thick dark mudstone of E₂l₂as the caprock and the good sealing of deep fault prevent the migration of oil and gas to the shallow.The difference in the maturity of source rocks between the East and west of the Fushan depression results in the oil and gas distribution law of"East gas and west oil".The dominant migration path of oil and gas controls the oil and gas distribution law of"Central and Eastern enrichment"in the Fushan depression;The stratigraphic and structural factors result in the oil and gas distribution law of"deep gas and shallow oil".