Effect of CO2/N2 Mixture Composition on Interfacial Tension of Crude Oil.

Abstract

CO2-enhanced oil recovery (EOR) has demonstrated significant success over the last decades; it is one of the fastest-growing EOR techniques in the USA accounting for nearly 6% of oil production. A large quantity of CO2 gas is required for the EOR process and sometimes other gases such as hydrocarbons, air, flue gases, CO2, N2, and mixtures of two or more gases are used for injection. It is also realized that the injection of CO2 and N2 combines advantage in reducing CO2 concentrations in the atmosphere and improving the oil recovery by sequestering it underground. However, there are a number of variables involved in the successful design of the CO2-EOR process. The objective of this study is to investigate the effect of CO2/N2 mixture composition on interfacial tension (IFT) of crude oil. Experiments were performed to measure the IFT of the CO2/N2 mixtures and crude oil for different compositions of gas by varying the system pressure at a fixed temperature. The effect of CO2/N2 mixture composition and pressure on the IFT of crude oil is evaluated. The experimental results show that an increase in the mole fraction of CO2 in the gas mixture results in a decrease in IFT between CO2–oil, irrespective of the system pressure. However, because of an increase in the mole fraction of N2 in the gas mixture, an increase in IFT was observed and this change is opposite to the effect of the CO2 mole fraction. Also, the change in IFT is consistent with the pressure, which means that the IFT decreases with an increase in the pressure at a given temperature. The effect of the CO2 mole fraction is more profound compared to the N2 fraction and with the pressure at which experiments were conducted in this study. The finding of this study helps in designing the CO2-EOR process in which achieving miscibility conditions is vital for taking advantage of the CO2 injection. Also, the presence of N2 and its influence on the IFT that must be considered in the CO2-EOR were addressed in this study.