A Molecular Level Study of Water-Oil Interface in the CO₂ EOR Under Low Pressure Condition

In this study, molecular dynamics simulations have been performed to study the interfacial properties between water and oil with different mole fractions of CO₂ under 8 MPa and 345 K. Simulation results show that with the increase of CO₂ mole fraction, more CO₂ got adsorbed in the water-oil interface region. Such CO₂ increase weakened water and oil interactions at the interface, resulting in a decrease of the interfacial tension (IFT). Moreover, the water-oil IFT decreased significantly from 0 to 0.40 CO₂ mole fractions. But the change was small for higher CO₂ mole fractions of 0.40 to 0.80. From those calculations, we conclude that in the CO₂-EOR, the volume of injected CO₂ needs to be at least more than 0.4 mole fraction (to the oil) to achieve a decent reduction of the water-oil IFT. This study can provide a molecular level reference for implementing the CO₂-EOR in the oil field under a low-pressure condition.