Miscibility Process of Hydrocarbon Mixture Gas and Crude Oil: Insights from Molecular Dynamics

Using molecular dynamics simulations, we investigate the miscibility process of hydrocarbon mixture gas and crude oil in Tarim Oilfield, which was not well understood from the microscopic points of view. The results show that the increase of the pressure of hydrocarbon mixture gas is favorable for the gas–oil miscibility until the interfaces vanish under a minimum miscible pressure (MMP). The identified MMP (37.3 MPa) is well consistent with the experimental value. With increasing gas pressure, the parallel diffusion coefficients of gas molecules in the gas–oil interfaces decrease, while the perpendicular ones increase. We also analyze the profiles of potential of mean force between different gas and various oil components, identifying the components which dominate the process of gas–oil miscibility from the perspective of molecular forces. In addition, the introduction of gravity in gas flooding slightly increases the MMP. These results can guide the optimization and design of the enhanced oil recovery technology with hydrocarbon mixture gas flooding.