Research On Tight Sandstone Oil Reservoir Microscopic Structure Of Chang 7 Member Of Triassic Yanchang Formation In Longdong Area,Ordos Basin

Chang 7 of the Triassic Yanchang Formation in Ordos Basin is a typical tight reservoir during the peak period of Lake Basin development.In order to solve the hot issue of obvious difference of oil reserves between different blocks in the same exploration area,this paper takes Chang 7 oil reservoir group in Longdong area as the target layer,combines the previous research results,carries out comprehensive research on the characteristics of sedimentary microfacies,physical properties,micropore throat structure,diagenesis,diagenetic facies reservoirs through core observation,thin section identification,high pressure mercury injection,constant velocity mercury injection and nuclear magnetic resonance and other experimental analysis techniques,analyses the formation mechanism of compact reservoirs,and classifies and evaluates the reservoirs.Longdong area is located on the slope of Yishan.Chang 7 of Yanchang Formation mainly develops deep lacustrine deposits.The lithology is dominated by mudstone and fine-grained sandstone.The reservoir is dominated by lithic feldspar sandstone with various fillings.The illite content is the highest,followed by chlorite,the sorting of sandstone is medium-poor,the compositional maturity and structural maturity are low,and the reservoir physical properties are poor as a whole.Reservoir pore types are mainly residual intergranular pore and dissolution pore.Various experimental methods show that Chang 7 reservoir in the study area has compact pore structure,strong heterogeneity,pore throat structure with large pore,fine roar,uneven distribution,and low mobile fluid saturation as a whole.The Chang 7 reservoir of Yanchang Formation in the study area has evolved to Medium Diagenetic A stage through compaction,cementation and dissolution.Based on the comprehensive analysis of diagenesis and rock association types,Chang 7 reservoir can be divided into five types of diagenetic facies: residual intergranular pore facies of chlorite film,dissolution facies of unstable components,weak dissolution micropore facies,illite cemented micropore facies and carbonate cemented compact facies.The physical properties of the first two types of reservoirs are relatively good,followed by illite cemented microporous facies and carbonate cemented dense facies.Based on the above analysis,the main reasons for densification of Chang 7 reservoir in Longdong area are sedimentation and diagenesis.The sedimentary microfacies control the development of dense reservoir and diagenesis changes the quality of reservoir.