Study On Features Factors Of Chang 7 Reservoir Of Yanchang Formation In Qingcheng Area,Ordos Basin

Ordos Basin is an ultra-large multi-cycle petroliferous basin and an important energy base in China,which is of great significance for ensuring China’s energy security.The research area in this paper belongs to Qingcheng Oilfield in Ordos Basin,which has entered the early stage of large-scale development of one million tons,but the reservoir physical property research of Chang 7 member of Yanchang Formation is relatively weak.It may become a factor restricting the sustainable development of oilfield in the later period.This paper takes the Chang 7 formation of Qingcheng Oilfield as the research object,combines the tectonic history and sedimentary characteristic background of Ordos Basin,adopts the lithology analysis method for the key Wells,adopts the idea from point to line and then connected,and divides the sedimentary facies of Chang 7 formation of Qingcheng oilfield.The macroscopic and microscopic characteristics of Chang 7 reservoir rock are analyzed by observing the core and thin section of rock and using the logging data.The sedimentary environment,lithology,rock particle strength,sorting,grinding,micropore and so on are studied.The relationship between the porosity and permeability of Chang 7reservoir was found and the reservoir classification was carried out based on logging interpretation data.SPSS system cluster analysis was adopted to study the heterogeneity of Chang 7 reservoir physical properties,and the following results were obtained:（1）The samples of black shale and chlorite indicate that the sedimentary environment of Chang 7 formation is deep lake and reducing environment;（2）The lithology is mainly lithic feldspar sandstone with stable clastic components and mica as the main interstitial material;（3）The granularity of rock particles is mainly fine sand and silty sand,with medium sorting and poor roundness;（4）Chang 7 reservoir is a low-porosity to ultra-low permeability reservoir with poor physical properties.The seepage capacity is controlled by micro-pore roar,but micro-fractures are developed.（5）There is a near linear relationship between porosity and permeability,and the average oil saturation is 61%;（6）The reservoir physical properties are very heterogeneous.Then it is concluded that the sedimentary background of Chang 7 reservoir in Qingcheng oilfield is a large inland depressed lacustrine basin,and the sedimentary facies are semi-deep lacustrine-deep lacustrine facies.Chang 7₁ and Chang 7₂ are the main reservoirs of this member,and their physical properties are generally poor,the sandstone types are mainly Lithic arkose and Lithic Arkose,which are brittle and easy to form a large number of three-dimensional micro-fractures under in-situ stress,and most oil and gas reservoirs are lithologic ones.