A Casestudy On Sedimentary Facies And Reservoir Characteristics Of Chang 8 Reservoir Group In Shanzhuang Area,Ordos Basin

Taking Chang 8 oil layer group of Yanchang Formation in Shanzhuang area as the research object,with using core analysis,slice identification observation analysis,scanning electron microscope test,logging and other data to finely divide and compare the characteristics of sedimentary facies,sand body distribution,reservoir characteristics,and pore evolution were comprehensively studied,and the comprehensive evaluation of the reservoir was finally carried out.According to the drilling data,the Chang 8 oil layer group is divided into 2 large cycles,each of which has a thickness of about 40m,and is divided into sub-sections of Chang 81 and Chang 82,of which Chang 81 is subdivided into three layers and Chang82 is subdivided into two layers,the thickness of the strata in the respective zones in the study area is relatively stable.According to the provenance analysis of the study area,it is found that the study area is mainly controlled by two-way provenances in southwest and northeast.The study found that the sedimentary facies of shallow water delta and lake mainly developed in the sedimentary period of the study area,and the subfacies were mainly the outer front of shallow water delta and the deposit of shallow lake.The Chang 8 oil layer mainly experienced two sedimentary periods of Chang 81 and Chang 82.Among them,the lake basin range was relatively shrunken and the sand body was well developed in the Chang 81 sedimentary period,while the water body range was large and the sand body was poorly developed in the Chang 82 sedimentary period.The main lithology of the reservoir sandstones in the Chang 8 oil layer in the study area is a set of gray-green fine sandstones.The rock type is mainly detrital feldspar sandstone and feldspar detrital sandstone,and some areas contain a small amount of feldspar sandstone;generally speaking,Debris types are mainly metamorphic rock debris,then magmatic rock debris,and the lowest content is sedimentary rock debris;interstitial material mainly includes clay mineral cement,carbonate cement,siliceous cement;pore type Mainly intergranular pores and feldspar dissolved pores,followed by debris dissolved pores and a small amount of micro-cracks.The reservoir porosity is mostly distributed between 5%and 8%,the average porosity is 6.02%,and the average permeability is 0.58×10^-3?m².Reservoir physical properties differ in different periods.Overall,Chang 81 reservoir physical properties are better than Chang 82.The types of diagenesis in the study area mainly include metasomatism,compaction,dissolution and cementation.After quantitative inversion of reservoir pore evolution,it is concluded that the original porosity in the study area is in the range of37.76%to 40.18%.The average pore loss caused by compaction is 22.75%,and the average pore loss caused by cementation and metasomatism is 9.89%,the average porosity increase rate caused by dissolution is 3.37%,and the existing porosity is between 5.98%and 18.85%.The favorable diagenetic facies belt of Chang 8 oil layer group in Shanzhuang area is mainly diagenetic facies of intergranular pores of chlorite thin film,diagenetic facies of illite cemented dissolved pores,and common type III and II+III reservoirs.