The Impact of Carbonated Water on Wettability: Combined Experimental and Molecular Simulation Approach

Summary Carbonated water injection has gained wide interest as an enhanced oil recovery technique. The efficiency of oil displacement during an ordinary waterflood is dictated and governed mainly by the viscous and capillary forces between oil and water. These forces are controlled by the interfacial tension (IFT) between the fluids and the contact angle (CA) with the rock surface. In this study, the pendant drop technique and molecular dynamics (MD) simulation were combined to investigate the effect of adding carbon dioxide on the water/oil/rock interfaces. CA measurement is rather a macroscopic assessment of the wettability while molecular simulation can provide further microscopic insights. The multiscale approach involves direct wettability assessment of asphaltene-containing oil against pure water or carbonated water, both exposed to two types of carbonate rock samples. Molecular characterization of asphaltenes was carried out by analytical means and different asphaltene structures were recreated on a computational platform for asphaltene-water and asphaltene-carbonated water molecular simulations. The experimental data revealed that the carbonated water caused the CA to change from weakly oil-wet to intermediate to water-wet wettability. Molecular simulation was invoked to shed more light into the underlying mechanisms behind the observed wettability alteration. In particular, molecular simulation of IFT and asphaltene swelling effect driven by the interactions with carbon dioxide were analyzed. The results were found consistent with the experiments. The findings presented in this paper highlight the viability of carbonated water for enhanced oil recovery and provide in-depth insights into the underlying mechanisms.