Study On The Characteristics Of Chang 7 Reservoir Of Yanchang Formation In Longdong Area,erdos Basins

In this paper,the shale of the Chang 7 Member of the Yanchang Formation in the eastern part of the Ordos Basin is elected as the object of study.With reference to a large number of literature and geological data of the study area,through field exploration,core description,special lithology sampling,the paper was guided by basic theories such as sedimentology,petroleum geology,and reservoir geology.This paper made full use of a variety of test and analysis methods such as thin section analysis,organic geochemical analysis and scanning electron microscopy to comprehensively evaluate the Chang 7 member shale,in order to find the favorable area of shale oil reservoir in this area.The thickness of Chang 7 member shale in the study area is about 100m-120m.The sedimentary facies types are mainly semi-deep lake-deep lake sediments and braided river delta deposits,which are favorable phase zones for organic-rich shale development.The lithology types developed in the sedimentary environment are mainly black mudstone,oil shale,carbonaceous mudstone and silty mudstone.According to the lithology and oilfield's actual requirements,the Chang 7 oil formation can be further divided into three small layer members,from Chang 7₁ to Chang 7₃,of which the regional marker bed“Zhangjiatan shale”is located in the Chang7₃ member position.There are three sources in the study area,the Qinling fold belt in the south is the main source supply area.Through the core description,the key well joint profile is established.It is found that there are multiple sedimentary centers in the study area and mud shale with a thickness of more than 60m is developed in the west of Jiyuan,east of Huachi,and Huanxian.Analytical and experimental data show that the type of shale organic matter is mainly type I and type II₁ kerogen,with high organic carbon content,low maturity and easy oil generation,and oil shale with high organic matter content has been found in the study area.As a place to store oil and gas,the storage space types of shale reservoirs in the study area are complex and diverse.Common pore types include intergranular pores,intragranular pores,organic pores and micro-cracks.Reservoir physical property analysis shows that the main distribution of mud shale porosity is between 6%and 10%,and the pores are well developed.The permeability of the reservoir is generally low,and the range is mainly between 0.1×10^-3?m² and 1×10^-3?m².Generally low.X-ray diffraction of whole rock analysis shows that the average brittle mineral content of mud shale exceeds 40%,and the shale reservoir can be modified easily.The oil-bearing conditions of shale oil reservoirs are very harsh,which are not only closely related to the organic matter type and maturity of shale,organic carbon content,lithofacies and reservoir space combination,but also shale thickness and fractureability.On basis of fully exploring the above factors,this paper establishes a shale oil reservoir evaluation system with organic carbon content and shale thickness as the main parameters,from which two shale oil reservoirs are preferred.Class area,3 category II areas and 1 prospect area.