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By using the data of logging, cuttings logging, thin section identification and analysis in the study area to study the four characteristics of the Nantun Formation reservoir and their relationship, the lower limit standard of effective reservoir physical property is established by the logging interpretation model of the reservoir mud content, porosity, permeability and saturation, and the mercury injection method, oil production method, oil test analysis method and cumulative frequency statistics method. The lower limit standard of effective reservoir electrical property is determined by using fluid identification chart. The results show that the lithology of the second member of Nantun Formation is mainly sandy conglomerate, and the first member of Nantun Formation is mainly sandstone, and the sandstone is more developed. The oil content is mainly full of oil, oil spots and oil stains. The reservoir porosity is between 4~20% and permeability is 0.01~100 mD, showing low porosity and low permeability. The lower limit of effective reservoir in Nantun Formation is porosity of 7%, permeability of 0.05mD, sonic time difference of 63μs/ft, density of 2.55 g/cm3 and water saturation of 20%.

Carbon dioxide miscible flooding has become one of the important technologies for improving oil recovery. The Minimum Miscible Pressure (MMP) is the key parameter to realize miscible flooding. As the MMP in the research area is higher than the formation fracture pressure, miscible flooding cannot be formed. To address this problem, it is necessary to find a way to reduce the MMP. Citric acid isobutyl ester is chosen to reduce the MMP of carbon dioxide and crude oil in this research. The effect of citric acid isobutyl ester on reducing the MMP was measured by the method of long-slim-tube displacement experiment. The experiment results show that the MMP is 29.6 MPa and can be obviously reduced by injecting the slug of citric acid isobutyl ester. The MMP could decrease gradually with constantly adding the injected slug of citric acid isobutyl ester, but the decrease becomes smaller and smaller. The optimum injected slug size of the chemical reagent is 0.003 PV. Under the condition of the slug size, the MMP is reduced to 23.5 MPa and the reduction is 6.1 MPa.