Research for reducing the Minimum Miscible Pressure of crude oil and carbon dioxide by injecting citric acid isobutyl ester

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.

A New Evaluation Way for the Adaptability of CO2 Flooding Reservoirs Based on Cluster Analysis

Carbon dioxide miscible flooding in oil reservoirs is a general method of enhancing oil recovery, nevertheless, not all reservoirs adapt to this method. Therefore, evaluating the adaptability of carbon dioxide flooding reservoirs becomes an important problem which is urged to be solved. Through the research of carbon dioxide flooding situation and displacement mechanism, twelve factors which influenced the oil displacement effect could be obtained. Compared factors with oil recovery by means of the advanced analysis of SPSS, and chose ten factors to be the evaluating indices which could apply in cluster analysis. Through building mathematical model and clustering reservoirs, the adaptability of carbon dioxide flooding could be evaluated comprehensively. Apply this method to cluster nine typical reservoirs which have adopted carbon dioxide flooding, the results show that, this method can evaluate the adaptability of carbon dioxide flooding reservoirs, which is corresponding to the real exploitation effect.

Characteristic Analysis of the Transition Zone in Carbon Dioxide Miscible Flooding

Study on the characteristic of the transition zone in CO2-oil system has important meaning for the research of CO2 miscible flooding. In this paper, one of crude oil samples in Xinjiang oilfield was taken as an example. The minimum miscible pressure (MMP) of CO2-oil system was confirmed through laboratory experiment and numerical simulation separately. And the characteristic of the transition zone was analyzed. The transition zone size and interfacial tension in miscible process were quantified. And their variation tendencies along with the change of the pressure and CO2 injection volume were studied. The results show that it is easier to reach miscible state in higher pressure and CO2 injection volume. This work provides a reference for the further research of CO2 miscible flooding.

Use CO2 Soluble Surfactant to Decrease the Minimum Miscibility Pressure of CO2 Flooding in Oil Reservoir

According to the mechanisms of carbon dioxide miscible flooding and previous researchers’ work on synthesis of CO2-soluble surfactant, Citric acid isoamyl ester was synthesized, and it’s oil solubility and the rate of viscosity reduction both in oil-water system and oil were evaluated. And then we found that this compound can solve in oil effectively; the optimum mass of Citric acid isoamyl ester introduced in oil-water system is 0.12g when the mass ratio of oil and water is 7:3 (crude oil 23.4g, formation water 10g) and the experimental temperature is 50°C , the rate of viscosity reduction is 47.2%; during the evaluation of the ability of Citric acid isoamyl ester to decrease oil viscosity, we found that the optimum dosage of this compound in 20g crude oil is 0.2g when the temperature is 40°C, and the rate of viscosity reduction is 7.37% at this point.