The Characteristics Of Chang 6₂ And Chang 6₃ Reservoirs And Its Oil Control In Foguyuan,Ordos Basin

According to the core observation,the sandstone in foguyuan area is mainly gray and grayish green,and the mudstone is mainly grayish black and black;there are a large number of plant fossil fragments in the hand specimens,and bivalve fossils are also found;all the above phenomena show that the target layer in the study area is in the underwater reduction environment.Combined with the reports,literatures and core observation in the adjacent area,it is considered that the front subfacies of meandering river delta developed in foguyuan area,and Chang 6₂²have the most developed underwater diversion channel.Due to the high density of well pattern,uniform thickness of small layers and no large-scale structural fluctuation in the study area,this paper establishes the sedimentary sand thickness index(F_f)based on the logging curve shape,and divides the main sedimentary microfacies developed in the study area into underwater distributary channel microfacies(F_f>0.60),underwater natural dike microfacies(0.3<F_f<0.6)and interdistributary bay microfacies(F_f<0.3).Through the observation of ordinary thin section,cast thin section,fluorescent thin section and scanning electron microscope,combined with high-pressure mercury injection and nuclear magnetic resonance,it is considered that the petrological characteristics of the whole reservoir in the study area are low mineral maturity and high structural maturity.The dissolution pores are dominant in Chang 6₂and Chang 6₃formations,followed by residual intergranular pores,and the pore throat of Chang 6₂²is the largest and the connectivity which is the best,and saturation of movable fluid is also the highest,Chang 6₃²is only behind Chang6₂².The layer in the study area is in stage A of late diagenesis,which dominated by lautonite cementation and chlorite cementation.The physical properties of the target formation in the study area are controlled by many factors,among which the physical properties of the underwater distributary channel micro channel reservoir are the best,and the distributary Bay micro channel reservoir is the worst.The more quartz particle content and laumontite content,the greater the porosity of the reservoir.Permeability is mainly related to the characteristics of pore structure.The larger the pore throat,the higher the permeability.Taking the sand body thickness,sedimentary sand thickness index,porosity,permeability and oil saturation as the basic parameters to evaluate the reservoir classification,the correlation between them and the stable oil production in the first year is established,and the comprehensive evaluation parameter(F)is established.The larger the F value is,the better the evaluation parameter is.When the comprehensive average parameter(F)is greater than 0.75,the reservoir belongs to class I reservoir,and the comprehensive average parameter(F)is between 0.55 and 0.75 When the interval is 0.35-0.55,the reservoir belongs to class III.when the comprehensive average parameter(F)<0.35,the reservoir belongs to class IV.Chang 6₂²formation is the most developed formation of type I and type II reservoirs,followed by Chang6₃²formation,which is the development place of high quality reservoirs.