Sandstone Reservoir Evaluation Of Shanxi Formation In The Middle East Of Ordos Basin

Ordos Basin is the second largest sedimentary basin in China,and the Shanxi period is an inland Craton basin with complicated cycles and many cycles.This paper takes the sandstone reservoir of the Shanxi Formation in the Middle-Eastern Ordos Basin as the research object.Based on the thorough investigation of domestic and foreign literature data and the digestion and absorption of previous research results,the overall research ideas and technical routes of reservoir evaluation work are used as guidance,combining previous research results with field surveys,core data,and logging data to divide the sedimentary facies in the study area;the reservoir petrology,hole features,physical properties,and diagenesis were thoroughly analyzed by means of casting thin slices,scanning electron microscopy,and mercury injection experiments;Finally,on the basis of the above research results,the grey correlation method was used to quantitatively analyze and classify the target area in the study area.The study shows that the Shanxi Formation in the Middle-Eastern part of the Ordos Basin mainly develops deltaic plain and delta front deposits.The two are roughly bordered by Tao 14-Tao 5-Shan 87-Hengshan County-Mi 42-Jia County,the delta plain is developed in the north and the delta front is developed in the south.The paper observes core coring data from 11 core wells and finds that both the cross-bed layering and hydrostatic horizontal layering with strong hydrodynamic effect in this area are more developed.The type of sandstone is mainly feldspar lithic sandstone,with high content of interstitials,high structural maturity,low compositional maturity,quartz content is high but not dominant,and argillaceous content in interstitials accounting for 68.69%,clay minerals are dominated by the smectite mixture layer,and sandstone structure maturity is medium-good.There are few pore and cracks,mainly developed dissolved pores and kaolinite intergranular pores,intergranular pores are not developed,throat types are mainly micro-throat,cracks mainly develop microfractures and mica fractures,and are now mostly in the late diagenetic stage A-B period.The overall pore structure can be divided into three categories:Type I is the low discharge pressure,medium-fine throat type;Type II is the low pressure,fine-micro throat type;Type III is the middle pressure,micro-throat Type,the permeability is mainly distributed between 0.1-1x10^-3?m²,which is a typical ultra-low porosity and ultra-low permeability tight sandstone reservoir.The paper study on the basis of reservoir petrological characteristics,pore and crack characteristics,physical properties,and diagenesis,using grey relational theory to classify reservoirs in the study area into three categories:Type I reservoirs,the porosity and permeability are better,mainly in the sedimentary environment of distributary channel and underwater distributary channel;Type II reservoirs are generally porous and infiltrated,it is mainly located in a mixed sedimentary environment of sand and mud,such as natural dike and underwater natural dyke;Type III reservoirs,with low porosity and permeability,mainly in sedimentary environments such as crevasse fans and mat sands,where the sand bodies are relatively pure but the thickness is small.