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The minimum miscible pressure is one of the key factors to realize miscible flooding. As the minimum miscible pressure 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 minimum miscible pressure. Citric acid isopentyl ester can not only be dissolved in crude oil, but also be dissolved in carbon dioxide. Therefore, citric acid isopentyl ester was chosen to reduce the minimum miscible pressure in this research. The effect of citric acid isopentyl ester on reducing the minimum miscible pressure was measured by the method of long slim tube displacement experiment. The minimum miscible pressure in the research area was 29.6 MPa. The experimental results show that the minimum miscible pressure could decrease significantly with increasing the injected slug size of citric acid isopentyl ester, but the decrease became smaller and smaller. The optimum injected slug size of the chemical reagent is 0.003 PV. Under the condition of the slug size, the minimum miscible pressure was 24.1 MPa. The reduction was 5.5 MPa. The reduction rate was 18.58%. The research results have important guiding significance for enhancing oil recovery in the research area. [ABSTRACT FROM AUTHOR]

As the minimum miscibility pressure in the research area is higher than the formation fracture pressure, it is impossible to form the miscible flooding. To address this problem, the effect of two chemical reagents (citric acid isobutyl ester, citric acid isopentyl ester) on reducing the minimum miscibility pressure (MMP) of carbon dioxide and the crude oil was determined through the long slim tube displacement experiment. The experimental results show that the minimum miscibility pressure could decrease significantly with increasing the injected slug size of the chemical reagents, but the decrease became smaller and smaller. The chemical reagents had an optimal injected slug size of 0.003 PV (pore volume). At such slug size, the minimum miscibility pressure for citric acid isobutyl ester was reduced by 6.1 MPa and for citric acid isopentyl ester the reduction was 5.5 MPa. The minimum miscibility pressure was reduced by 20.61% and 18.58%. The addition of citric acid isobutyl ester slug could greatly reduce the minimum miscibility pressure, with a better effect. The recovery of the miscible flooding experiment scheme after injection of citric acid isobutyl ester slug was higher by 6.5%–11.6% than that of the scheme without citric acid isobutyl ester injection. Therefore, the citric acid isobutyl ester was recommended as the best chemical reagent to reduce the minimum miscibility pressure. The research results are of certain guiding significance for the overall realization of miscible flooding to enhance oil recovery in the research area. • Two chemical agents were prepared by optimizing the preparation process. • The minimum miscibility pressure decreased significantly with increasing the injected slug size of the chemical reagents. • The chemical reagents had an optimal injected slug size of 0.003 PV. In this case, the MMP was reduced by 20.61% and 18.58%. • The recovery after injection of citric acid isobutyl ester was higher by 6.5% to 11.6% than that of without injection. [ABSTRACT FROM AUTHOR]