Carbonate Rock Microbial Construction And Reservoir Characteristics Of Sinian Dengying Formation In The Eastern Sichuan Basin

Based on the Dong'an Kanggu section,Pengshui Liaojiacao section and well w,this thesis uses measurement of field outcrops,core observation,thin section identification,cathodoluminescence analysis,SEM and geochemical analysis to analyze the rock type,macrostructure,meso characteristics,micro fabrics,microbial types and structures,development environment,sedimentary microfacies,distribution and storage,reservoir space,physical properties,bitumen,diagenesis,diagenetic sequence and diagenetic fluid of Dengying Formation microbialites in the East Sichuan.Finally,this thesis discusses the characteristics of microbial formation,reservoir characteristics and the main controlling factors of reservoir development.The microbial construction can be divided into the microbial mound and the microbial stratum.The microbial mounds are mainly developed in the 2^nd member of Dengying Formation.They are mainly composed of thrombolite,stromatolite and spongiostromata.And most of them are superimposed.The 4^th member of Dengying Formation mainly develops the microbial stratum,which is mainly lamina-thin layer.The microfabric of the microbialites is divided into thrombolite,stromatolite,spongiostromata,coating fabric and dendritic fabric.A total of 11 types of cyanobacteria were identified.SEM shows spherical,spherical aggregates,rods and other forms of the cyanobacteria.Microbialites are developed in the limited water environment of anoxic reduction,arid climate and high salinity.The Dengying Formation in the study area is mostly platform margin or limited platform facies deposition.Microbialites are divided into 10 sedimentary microfacies,namely,thrombolite,stromatolite,thrombolytic stromatolite,spongiostromata,microbial grid rock,window lattice cohesive rock,cohesive aggregate rock,oncolite binding rock,spheric granular rock and grape-lacelike dolomite.The microbial mounds and shoals in the platform margin are developed in the eastern basin margin and near the Mianyang-Changning intracratonic sag in the west.The intra-platform microbial mounds and shoals can be seen in the Dazhou-Xuanhan area.The reservoir space types are mainly intergranular pores,dissolution pores and holes,and the reservoir physical properties of 4^th member are better than that of 2^ndmember.Reservoir bitumen is mainly developed on the top of the 4^th member of Dengying Formation,and it is distributed in spots or impregnations.It is filled in intergranular pores,dissolution pores and holes,and a small amount is distributed along sutures or cracks.There is also a small amount of reservoir bitumen development in the2^nd member of Dengying Formation.The diagenesis sequence is:microbial mud crystallization?microbial dolomite?seawater cementation?meteoric water dissolution and cementation during the syn-sedimentary stage?first stage tectonic rupture?first stage silicification?epigenic karstification?shallow burial dissolution and cementation?second stage tectonic rupture?first stage hydrocarbon filling?second stage silicification?medium and deep burial dissolution and cementation?second stage hydrocarbon filling.The diagenetic fluid is mainly sea water with high salinity,which is partially transformed by hydrothermal process.The reservoir of Dengying Formation in the study area is mainly controlled by the following three aspects.Firstly,the sedimentary microfacies such as thrombolite and stromatolite are the material basis for the development of high-quality reservoir.Secondly,the epigenic karstification caused by Tongwan movement and the dissolution during the burial period are important for the reconstruction of high-quality reservoir.Finally,hydrocarbon filling is conducive to the later preservation of reservoir space.