Reservoir Characteristics Of Neogene Youshashan Formation In Nanyishan Oilfield,Tsaidam Basin

In this paper,the Neogene Youshashan formation in Tsaidam Basin is taken as the research target layer,and the research area is mainly the Nanyishan area in the northwest of Qaidam Basin.Through collecting literature,consulting data,on-site core description and systematic sampling analysis,using geophysical methods such as logging,on the basis of oil and gas reservoir geology,combined with the relevant theories of sedimentary petrology and other disciplines,this paper makes a detailed description and Research on the characteristics of Neogene Youshashan formation carbonate reservoir in Nanyishan Oilfield.In this paper,the reservoir rocks of Neogene Youshashan formation in Nanyishan oilfield are divided into four types,include: Algae Limestone,limestone(dolomite),mudstone,sandstone,each type of lithology can be subdivided into 2-4 kinds of lithology,so this paper divided into 12 kinds of lithology;The algal limestone is mainly composed of algal agglomerates and algal laminated sedimentary structures;Limestone,mudstone and sandstone are mainly massive and horizontal bedding.Through on-site core description and statistical analysis of porosity and permeability data of each lithology,it is concluded that algal limestone and limestone are the favorable lithology for reservoir.Through the research on the microstructure of the reservoir stratum,11 types of reservoir space are classified,including primary intergranular pores,intergranular dissolved pores,intercrystalline pores,necking throats,and tubular throats.After the lithology statistics of the oil groups in the study area,it was found that oil groups I and II were mainly dominated by limestone(dolomite),while oil groups III,IV and V were mainly dominated by mudstone.Combined with the results of single well core fine description and logging interpretation in the study area,seven kinds of sedimentary structures and sedimentary microfacies with typical characteristics are divided,and then the plane distribution of sedimentary facies is studied.It is considered that the distribution of dominant facies zones of Neogene Youshashan formation in Nanyishan oilfield is relatively contiguous.By analyzing and studying the thin sections of the target layer samples in the study area,it is found that dissolution and cementation,which are beneficial to the development of pores,are common,and the effects of various diagenesis on the physical properties of the reservoir are described in detail.Based on the determination of stable carbon and oxygen isotopes in the samples,three diagenetic environments can be divided into lake bottom diagenetic environment,atmospheric fresh water diagenetic environment and burial diagenetic environment.