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

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.