Sedimentary Facies And Reservoir Characteristics Of Fine-Grained Sedimentary Rocks

The western part of the Qaidam Basin is the key oil and gas exploration and development area in the Qaidam Basin.It has the characteristics of mixing,wide distribution,rapidly variable facies and strong heterogeneity.The division of fine-grained sediments,the distribution characteristics of sedimentary facies,and the research on the diagenetic evolution stage of reservoirs have not been thoroughly studied,which hinders the oil and gas exploration progress of the Shangganchaigou Formation-Xiayoushashan Formation in this area.Based on the data of cores,rock slices,mineral X-ray diffraction,porosity and permeability experiments and trace elements,this paper comprehensively analyzes the lithological characteristics,laminar development characteristics and deposition of fine-grained sediments of the Shangganchaigou Formation-Xiayoushashan Formation in the western Qaidam Basin.According to the distribution characteristics of facies,the research on reservoir characteristics and diagenetic evolution characteristics was carried out,the diagenetic stage of fine-grained sediments reservoirs was clarified,the controlling factors for reservoir development were determined,reservoir evaluation standards were established,and finally favorable area development was carried out.cloth forecast.The research indicates that there are four types of fine-grained sediments in the Shangganchaigou Formation-Xiayoushashan Formation in the western Qaidam Basin,among which the mixed rock is the most developed,followed by the lime-bearing dolomite.It can be further divided into 9 categories;the fine-grained sediments in the study area are widely developed with silty laminae,clay laminae and carbonate laminaehey,and they form 2 kinds of laminae set: clay laminae + silty laminae,carbonate laminae + clay laminae.It was widespread development of carbonate laminae +clay laminae in the Shangganchaigou Formation-Xiayoushashan Formation and the relative development of clay laminae +silty laminae in the Shangganchaigou Formation.In the study area,three independent sedimentary systems developed during the depositional period of the Shangganchaigou Formation-Xiayoushashan Formation.Xianshuiquan area near Altun Mountain is a semi-deep lake sedimentary area is a semi-deep lake sediments with developed mud from intermediate depth lake and sandy debris flows.Jiandingshan-Fengxi-Nanyishan-Xiaoliangshan area in the northern part of the study area is dominated by shallow lake sediments,and shallow lake lime mud flats,calcite dolomite flats and sand flats are widely developed,and algal limestone are widely developed;the Youquanzi-Huangguamao-Kate area in the south of the study area is dominated by shallow lake sediments influenced by meandering river deltas with sand flats and algal mats developed.The dominant reservoir rock type of Neogene fine-grained sediments in the western Qaidam is massive/laminated lime dolomite,followed by massive/laminated siltstone;the reservoir space is dominated by intercrystalline pores,dissolution pores,primary porosityan and crack.It belongs to the ultra-low porosity-low permeability tight reservoir as a whole.The fine-grained sediments of the Neogene Shangganchaigou Formation-Xiayoushashan Formation in the study area are mainly in Period B of early diagenesis to t Period A of middle diagenesis.The sedimentary microfacies,reservoir burial depth,diagenesis and laminar development characteristics jointly affect the reservoir quality.Based on the physical properties and diagenetic evolution characteristics of Neogene fine-grained sediments reservoirs in the western Qaidam Basin,the evaluation criteria for fine-grained sediments reservoirs in this area are established.The Youquanzi-Huangguamao,Fengxi-Nanyishan areas are selected as favorable reservoir distribution areas for fine-grained sedimentary rocks of the Shangganchaigou Formation,and the Xianshuiquan,Youquanzi-Huangguamao,Fengxi-Nanyishan and Jiandingshan areas are selected as favorable reservoir distribution areas of Xiayoushashan Formation.