The Oil-bearing Characteristics And Main Controlling Factors In The Second Member Of Funing Formation In Gaoyou Sag And Jinhu Sag

The Gaoyou sag and Jinhu sag in the Subei Basin have developed multiple stratums of shale,with great potential for shale oil resources.Accurate evaluation of oil contents and characterization of its spatial distribution are the keys to clarifying the distribution of shale oil resources and selecting favorable exploration targets.The shale in E₁f₂ has strong heterogeneity in many aspects,such as lithofacies,hydrocarbon generation quality,storage conditions and oil contents.The lack of accurate parameters to characterize oil contents and the unclear understanding of the main controlling factors of oil contents restrict the further development of shale oil exploration in the study area.In this paper,based on a large number of core observations,petrology,organic geochemistry,and reservoir tests,the oil-bearing property and mobility of the shale in the second member of the Funing Formation（E₁f₂）,Gaoyou sag and Jinhu Sag,Subei Basin,are quantitatively characterized.The heterogeneity characteristics of lithofacies,hydrocarbon generation,reservoir and oil-bearing property of E₁f₂ are discussed.The controlling effect of above-mentioned different factors on the oil-bearing property of shale is analyzed.Based on experiments such as X-ray diffraction,rock thin section,conventional pyrolysis,nitrogen adsorption,nuclear magnetic resonance,and argon ion polishing-field emission scanning electron microscopy,this paper describes the heterogeneous characteristics of lithofacies,hydrocarbon generation and reservoir of the shale oil formed in E₁f₂ in the study area.A total of 24 types of lithofacies and 4 types of pore structures have been identified in E₁f₂.Ye 1 and 2 sub-members have better hydrocarbon generation quality than the other.The restoration model of light hydrocarbon losses during the stage of sample preservation and sample pretreatment is established,and the light hydrocarbon losses in the Gaoyou sag and Jinhu sag are 0.4～1.2 times the measured oil contents.Shale oil in different occurrence states by multistep pyrolysis method and two-dimensional nuclear magnetic resonance experiments is quantitatively characterized.The total oil contents,free oil contents and movable oil contents are 2.831,1.861 and 0.774 times corrected pyrolysis hydrocarbon.Comparing various artificial intelligence methods,the Random Forest method was selected to predict shale oiliness parameters.Vertically,the shale in the Ye 4 sub-member of Jinhu sag has the best oil-bearing property and mobility.The average total oil contents in the deep concave zone is 2.88 mg/g,and the average OSI is43.04 mg/g.The shale in Ye 5 sub-member of Gaoyou sag has the best oil-bearing property and mobility.The average total oil contents in the deep concave zone is 4.28mg/g,and the average OSI is 138.11mg/g.In the rich shale oil interval,the oil-bearing property and mobility of the shale in Gaoyou sag are better than those in Jinhu sag.On the plane,the deep concave zone of Gaoyou sag and Jinhu sag has the best oil-bearing property and mobility,and oil-bearing property and mobility become worse in a ring-like shape toward the slope.The relationship between lithofacies,hydrocarbon-generating quality,reservoir quality,abnormal pressure and oil-bearing property is discussed,so as to clarify the differences in the controlling effects of different factors on shale oiliness.High organic matter abundance（TOC>2%）,good organic matter type（Type I and II₁）and moderate maturity（Ro=0.8～1.1%）are the main controlling factors for the oil-bearing property heterogeneity of the shale in E₁f₂.The hydrocarbon generation conditions of shale oil in the Gaoyou sag are better than those in the Jinhu sag.Lithofacies control the pore characteristics and physical properties of shale reservoirs.Type I and II pore-structured shales in E₁f₂ have the best oil-bearing property,and are mainly developed in the organic-rich-felsic fine-grained mixed sedimentary rocks in the Gaoyou Sag and in the organic-rich-carbonate fine-grained mixed sedimentary rocks in the Jinhu Sag.These lithofacies are also favorable lithofacies for the enrichment of shale oil in E₁f₂.