Molecular Insights into Effects of Methanol Additive on CO2 Enhanced Oil Recovery in the Dead-End Nanopore

In unconventional reservoirs, the water film at the entrance of the dead-end nanopore brings obstacles to CO2 injection for displacing the residual oil. Thus, the structure and stability of the water film become key factors during oil displacement. Herein, we carry out molecular dynamics (MD) simulations to explore the effects of adding methanol to the CO2 injection flow on the interfacial properties of the water film. In the two-phase system, our results reveal that methanol would affect the surrounding water molecules at the interfacial region significantly, leading to a reduction in interfacial tension and a decrease in the interface stability. In the dead-end pore system, methanol is crucial for disrupting the hydrogen bond (H-bond) network and changing the deformation pattern of the interface, which leads to the earlier rupture of the water film. This work provides molecular insights into the water film rupture and offers a theoretical approach to carbon dioxide enhanced oil recovery (CO2-EOR) in unconventional reservoirs in the high water-cut stage.