Reservoir Characteristics And Favorable Reservoir Prediction Of Paleogene Shahejie Formation In Cangdong Sag

Cangdong sag studied in this paper is one of the two important oil-gas rich depressions in Huanghua depression of Bohai Bay basin.In recent years,the progress of oil and gas exploration is mainly concentrated in Kongdian formation of Paleogene in Cangdong sag.Compared with Kongdian formation,Shahejie formation,as a backup Exploration Series,has relatively less in-depth study.The low mature source rocks are widely developed in Cangdong sag during Shahejie period,and the existing oil and gas show up in the clastic rock sedimentary system of the third member of Shahejie Formation and the carbonate rock sedimentary system of the first member of Shahejie formation,showing good oil and gas exploration prospects.With the continuous enrichment of basic data and further exploration,the importance of in-depth study on the reservoir characteristics and distribution of Shahejie Formation in Cangdong sag is self-evident.In this paper,with the help of a variety of reservoir analysis and testing techniques,the general characteristics of carbonate reservoir and clastic reservoir developed in the first member of Shahejie Formation and the third member of Shahejie Formation in Cangdong depression are studied;the distribution characteristics of reservoir physical properties in plane and vertical are analyzed,and the key reservoirs are classified and evaluated and favorable reservoir prediction are made.Combined with the existing basic data,and using thin section analysis,SEM analysis and mercury injection analysis,(1)the results show that compaction,cementation,metasomatism and dissolution are the main diagenesis of Shahejie Formation reservoir in Cangdong depression.Based on the comprehensive study and analysis of vitrinite reflectance(RO),clay mineral assemblage and evolution law,as well as the occurrence and distribution of authigenic minerals in the collected samples,the diagenetic stage of the clastic reservoir developed in Shahejie formation of Cangdong depression is divided into early diagenetic stage a ? middle diagenetic stage A1,and the carbonate reservoir developed is divided into quasi syngenetic stage ? middle diagenetic stage A1.(2)According to the analysis of thin sections,the main types of reservoir space are primary intergranular pores and secondary solution pores.The variation of reservoir porosity and permeability is mainly caused by compaction and cementation in reservoir diagenesis.Later,in the area with larger burial depth,the reservoir is affected by the dissolution of acid fluid,resulting in secondary pores,which greatly improves the physical properties of the reservoir.In the carbonate reservoir developed in the first member of Shahejie formation,secondary pores and fractures are the main reservoir space.Under the control of the dissolution of acid fluid and the leaching under the unconformity surface,multiple secondary pore zones are developed longitudinally.(3)There are three main factors affecting the development of the reservoir,which are sedimentation,structure and diagenesis.Based on this,the classification and evaluation criteria for the development of Shahejie Formation reservoir in Cangdong sag are established,and the reservoir evaluation is carried out for the clastic reservoir in the third member of Shahejie Formation and the carbonate reservoir in the first member of Shahejie formation.The results show that the fan delta front sand body of the third member of Shahejie Formation in Cangdong sub sag steep slope zone,the shore shallow lake beach bar sand body around Kongdian uplift and the braided river delta front sand body around Nanpi sub saggentle slope are the favorable reservoir zones for clastic reservoir,and the grain debris Beach around Kongdian uplift in the first member of Shahejie formation is the favorable reservoir zone for carbonate reservoir.