Molecular Dynamics Studies of Fluid/Oil Interfaces for Improved Oil Recovery Processes

In our paper, we study the interface wettability, diffusivity, and molecular orientation between crude oil and different fluids for applications in improved oil recovery (IOR) processes through atomistic molecular dynamics (MD). The salt concentration, temperature, and pressure effects on the physical chemistry properties of different interfaces between IOR agents [brine (H2O + % NaCl), CO2, N-2, and CH4] and crude oil have been determined. From the interfacial density profiles, an accumulation of aromatic molecules near the interface has been observed. In the case of brine interfaced with crude oil, our calculations indicate an increase in the interfacial tension with increasing pressure and salt concentration, which favors oil displacement. On the other hand, with the other fluids studied (CO2, N-2, and CH4), the interfacial tension decreases with increasing pressure and temperature. With interfacial tension reduction, an increase in fluid diffusivity in the oil phase is observed. We also studied the molecular orientation properties of the hydrocarbon and fluids molecules in the interface region. We perceived that the molecular orientation could be affected by changes in the interfacial tension and diffusivity of the molecules in the interface region with the increased pressure and temperature: pressure (increasing) -> interfacial tension (decreasing) -> diffusion (increasing) -> molecular ordering. From a molecular point of view, the combination of low interfacial tension and high diffusion of molecules in the oil phase gives the CO2 molecules unique properties as an IOR fluid compared with other fluids studied here.