Shale Reservoir Quality Of The Second Member Of Funing Formation In Gaoyou Sag And Jinhu Sag,subei Basin

With the exploration and development of shale oil and gas resources in China,the continental shale oil shows great resource potential.Since the shale oil reservoir in the continental lake basin is obviously heterogeneous with complex lithology and lithofacies,the omni-directional evaluation of shale oil reservoir quality is a key part of the shale oil exploration and development.Shale oil has been seen in many wells of the second member of the Funing Formation（E₁f₂）in Gaoyou sag and Jinhu sag.In this paper,we selected multiple wells in E₁f₂ of Gaoyou and Jinhu sags in the Subei Basin to carry out fine core observation and description,thin section,argon ion polishing SEM,X-ray diffraction,nitrogen adsorption,high-pressure mercury injection and NMR techniques with fractal analysis methods to finely characterize the lithofacies,reservoir space,pore structure and reservoir physical property heterogeneity in the E₁f₂.The study shows that the vertical distribution of lithofacies in E₁f₂ shale reservoir is controlled by sequence framework,and the longitudinal variation of heterogeneity is obvious.The types and distribution of reservoir space are complex,dissolution pores and clay mineral intercrystalline pores are well developed in mineral matrix pores,organic matter pores are mainly developed in deep concave belts and diabase intrusive metamorphic belts in the study area,and structural microfractures are well developed,mainly in Ye 4 and Ye 5 sub-member.The pore diameter of shale reservoir in E₁f₂ member is mainly 10nm～200nm,and the average proportion of macropore in Jinhu sag is 11.04%higher than that in Gaoyou sag.The pore structure can be divided intoⅠ,ⅡandⅢtypes,in which the pore space development and the reservoir performance ofⅠpore structure is the best,the pore surface of Gaoyou sag is rougher than that of Jinhu sag,and the pore structure is more complex.There are more carbonate interbeds in the Gaoyou sag,mainly in each sub-formation of the deep southeast concave belts,while sandstone interbeds are more developed in the Jinhu sag,and the interbeds are mainly in the Ye 4 and Ye 5 sub-member in the center of each sub-sag.The reservoir physical properties are longitudinally and planarly heterogeneity,and the high-value areas are mainly in the interbeds development section in the study area,The average physical property of Gaoyou Sag is 5.02%,and that of Jinhu Sag is 5.61%,higher than Gaoyou Sag.The heterogeneity of the reservoir in the study area is mainly influenced by the mineral composition contents,organic matter hydrocarbon generation and diagenesis.Mineral composition mainly affects the type of reservoir space and physical properties of shale oil reservoirs,carbonate minerals and analcime contents can produce plenty of dissolution pores,resulting in the increase of physical properties;the sedimentary environment with high abundance of organic matter is not conducive to the development of reservoirs and the decrease of reservoir physical properties,high maturity organic matter can produce organic acid dissolution pores and organic matter pores in the process of hydrocarbon generation,which can improve the reservoir space of shale oil reservoir;the constructive diagenesis in the study area is mainly fracture,dissolution and clay mineral transformation,and destructive effects are mainly compaction and cementation.A large amount of diabase intrusions can be seen in E₁f₂ of Gaoyou sag,and the reservoir space and pore structure of the metamorphic belt above and below the intrusive body have been greatly improved,and the nitrogen adsorption capacity can reach 1.66 times of shale.Based on the analysis of the influencing factors of reservoir physical property heterogeneity,the evaluation criterion of the shale oil reservoir quality of the E₁f₂ in the study area is established,and the reservoir quality is divided into three categories,The reservoir quality score of Ye 4 and Ye 5 sub-member in Gaoyou sag and Jinhu sag is the highest,with an average of 0.85 and 0.88.The first category of reservoir is mainly in the deep depression zone of the two sags,which provides a reference for the subsequent shale oil exploration and development.