Genetic Type And Distribution Pattern Of Crude Oil In The West Of Bozhong Subsag And Peripheral Area

Located in the northwest of Bozhong sag,the west of Bozhong subsag has developed a steep slope zone and a central strike-slip zone,and it is the main site of oil and gas accumulation.Based on the geochemical analysis data of cuttings and core samples,combined with drilling and seismic data,this paper studies the geochemical characteristics and development distribution rules of the hydrocarbon source rocks in this area,as well as the organic geochemical characteristics and sources of crude oil.On this basis,it classifies the types of crude oil and explores the geological control factors for oil and gas reservoir formation.The abundance,type and maturity of organic matter in source rocks were described in detail by the composition of kerogen elements,pyrolysis parameters of source rocks,maceral content and vitrinite reflectance.The result shows that three sets of hydrocarbon source rocks with high abundance of organic matter in the west of Bozhong subsag,mainly II type of organic matter,in the mature stage of evolution.The third member of Dongying Formation has the widest distribution range of hydrocarbon source rocks,and the third member of Shahejie Formation has the smallest distribution range of hydrocarbon source rocks,but its thickness is the largest.The sedimentary environment characteristics of source rocks and the input contribution of organic matter are discussed by using the biomarkers of saturated and aromatic hydrocarbons.Based on the overall analysis of the geochemical characteristics of crude oil,including physical properties,group composition,gas chromatography of saturated hydrocarbons,carbon isotopes composition and biomarkers characteristics,it is shown that crude oil is a mixed type(II)organic matter and sedimentary environment in weak oxidation-reduction.On this basis,the hydrocarbon source rocks and crude oil are compared and analyzed by cluster analysis and biomarkers scatterplot.The results show that the oil source rocks in the study area are mainly the source rocks of Shahejie Formation and Dongying Formation.The crude oil can be divided into three types by oil source comparison.There are both single source crude oil and mixed source crude oil.Finally,the source and controlling factors of crude oil in CFD6-2 reservoir are studied from the aspects of the development and distribution of hydrocarbon source rocks,the comparison of oil and source rocks,migration and accumulation.The results show that the source rocks of this oilfield are good source rocks,which can provide necessary material premise for oil and gas accumulation.The fault energy of oil source with long duration of activity penetrates to the basement and extends upward to the shallow Neogene system as the main channel of oil and gas vertical transmission.The late secondary faults will form fractures in the shallow part,which can distribute the oil and gas transmission to the Minghua Formation.