Discrimination And Hydrocarbon Expulsion Characteristics Of Effective Source Rocks Of E₂l₂ In Fushan Sag

The Fushan Sag has excellent rolling development results and great potential for exploreable resources.However,with the improvement of the degree of exploration,it is urgent to find advantageous exploration areas in order to seek new areas for increasing reserves and increasing production.Source rocks are the key to determining the potential of oil and gas resources.There are many sets of source rocks in the Fushan Sag,but the distribution and expulsion characteristics of effective source rocks are unclear,which restricts the understanding of resource potential and the selection of favorable resource fields.Therefore,this paper selects the main source rock layer in Fushan Sag—E₂l₂to carry out shale distribution characteristics and quality evaluation,and at the same time conducts effective source rock identification and hydrocarbon expulsion characteristics research to further deepen the systematic understanding of source rocks in the study area.It provides a resource knowledge basis for further research on the conditions of oil and gas migration,accumulation and accumulation in the Fushan Sag,and provides guidance for the selection of favorable resource areas in the study area.Through the statistics of the thickness of dark mudstones of different lithofacies,combined with the analysis and test data of organic matter abundance,the paper determines that dark（taupe,dark gray,grayish black,gray and black）mudstones are the main source rock types,combined with the constraints of sedimentary facies,the plane distribution characteristics of source rocks are predicted,and it is revealed that the areas with high thickness are mainly located in the Huangtong sub-sag in the west and the Bailian sub-sag in the east.According to the comprehensive evaluation of the organic geochemical characteristic parameters of the source rocks of each submember of E₂l₂,it is clear that the abundance of organic matter is relatively high,the organic carbon content is between 0.16%and 3.05%,the average is 1.71%,and the hydrocarbon generation potential is medium,the types of organic matter are mainly typeⅡ₁andⅡ₂,which are in the mature-high maturity stage.In general,the quality of source rocks in E₂l₂²is better than that of the E₂l₂¹.The hydrocarbon generation potential method is used to determine that the hydrocarbon expulsion threshold of source rocks of E₂l₂is R_o=0.66%,and the TOC lower limits of effective source rocks are 0.9%and 1.1%,The distribution of effective source rocks is mostly concentrated in the deep depressions of two sub-sags.,the thickest part is located in the Bailian sub-sag in the east of the Fushan Sag,up to more than 450m,extending from the center of the sag to the edge and the central uplift belt.According to the hydrocarbon expulsion model,when R_ois 0.80%,the source rock reaches the peak of hydrocarbon expulsion,and the maximum hydrocarbon expulsion efficiency can reach 97.7%.The Huangtong sub-sag in the west and the Bailian sub-sag in the east are the main hydrocarbon expulsion areas.The hydrocarbon expulsion intensity of the E₂l₂¹and E₂l₂²can reach up to 184.22×10⁴t/km²and45.39×10⁴t/km²,and the cumulative hydrocarbon expulsion amounts are 52.99×10⁸t and15.58×10⁸t.