Distribution Characteristics Of Source-Reservoir Assemblage Of Lucaogou Formation In Jimsar Sag,Junggar Basin

Jimsar Sag is one of the earliest areas in China to explore and develop tight oil,and the Permian Lucaogou Formation is the main target stratum of the sag.The study of source-reservoir assemblage and its distribution characteristics is very important for predicting the sweet point in tight oil.Previous studies on the source-reservoir assemblage of Lucaogou Formation in this area were mainly confined to the upper and lower sweet spots in terms of horizon,and focused on the spatial configuration relationship between source rock and reservoir.However,the study on the whole Lucaogou Formation is not systematic enough,and there are few studies on the differences of source-reservoir assemblage in reservoir formation.Therefore,it is difficult to form an overall understanding of tight oil accumulation in this area.In this thesis,the characteristics of source-reservoir assemblage of Lucaogou Formation in this area are systematically classified and evaluated from the aspects of fine-grained rock lithology identification,isochronous stratigraphic division and correlation,source rock characteristics evaluation,reservoir characteristics evaluation,tight oil accumulation analayses and so on.Based on the analysis of rock-electric relation of standard wells,the identification charts of 3 categories and 6 subcategories of lithology are established.On the basis of dividing the paleosalinity cycle of Lucaogou Formation by environmental geochemical parameters,and combining with the characteristics of lithologic assemblage,the Lucaogou Formation is subdivided into 8sections,and the stratigraphic correlation in the whole area was completed by using oil shale and other marker layers.The study of source rocks shows that the types and abundance of organic matter in Lucaogou Formation are similar,which is mainly affected by sedimentary environment.The source rocks formed in the period of high salinity water have high hydrocarbon generation efficiency,while the source rocks formed in the period of low salinity water are relatively low.On the whole,the quality of source rocks in the lower member of Lucaogou Formation is better than that of the upper member.The study of reservoir shows that siltstone and argillaceous siltstone are the best reservoirs in Lucaogou Formation,in which the upper member of Lucaogou Formation has a large thickness and good transverse continuity,while the lower member has a small thickness and poor lateral continuity.The study of sedimentary facies indicates that delta,shoreshallow lake and semi-deep lake facies were mainly developed in the sedimentary period of Lucaogou Formation.Mouth bar microfacies in delta front and sand flat microfacies in shoreshallow lake are important microfacies for the development of high-quality reservoirs,and they are most widely distributed in section B and G.Reservoir peforphysical properties are mainly controlled by lithology and dissolution,and also affected by the peak of hydrocarbon generation.The analysis of accumulation model shows that the oil and gas in the upper member of Lucaogou Formation experienced long-distance vertical and horizontal migration,while the oil and gas in the lower member are mainly formed by near source or within source.Based on the above factors and oil test data,the source-reservoir assemblages of Lucaogou Formation are divided into 3 categories and 7 subcategories,among which typeⅠ₂and typeⅡ₂are the most favorable for tight oil accumulation.Based on this,the favorable areas for tight oil accumulation of Lucaogou Formation in Jimsar Sag are predicted.