Interfacial interactions between Bakken crude oil and injected gases at reservoir temperature: A molecular dynamics simulation study

Abstract

Due to large amounts of oil remain in the Bakken Formation, an effective enhanced oil recovery (EOR) method is crucially important. Cyclic gas injection, like CO2, methane, and ethane, can mobilize the residual oil and enhance oil recovery. In this study, the gas solubility, volume swelling factor, oil diffusion coefficient, and minimum miscibility pressure (MMP) were studied to compare the efficiency of different gases in the EOR process. Based on the Bakken oil components, a molecular model of the crude oil containing different types of alkanes was built. A series of molecular dynamics (MD) simulations were carried out to study the interfacial interactions between Bakken crude oil and the injected gases. At various pressures and reservoir temperature, density profiles were plotted to show the distribution of different components, and the solubility of gases in crude oil was calculated. The swelling factor was obtained by comparing the density of gas-saturated crude oil and that of the pure crude oil. The vanishing interfacial tension (VIT) method was used to determine the MMPs. The simulation results show that all three gases hold great potential in further improving oil recovery. As the pressure increases, the gas solubility increases, and the interfacial width becomes wider. At constant temperature and pressure, ethane holds the highest solubility in crude oil and can induce the most pronounced oil swelling. Meanwhile, ethane can achieve the lowest MMP and the most significant oil diffusion coefficient, which means ethane is most effective in mobilizing and producing crude oil from the reservoir.