Unveiling the Chemical Interactions of Calcium Ions with Surface-Active Components in Water-Crude Oil Emulsions

Emulsion formation presents a significant operational challenge in oil production, necessitating the continuous development of novel and effective demulsification methods. However, the lack of a fundamental understanding of the mechanisms that regulate the formation of these emulsions significantly complicates this process. In this study, we systematically investigated the influence of Ca²⁺ ions on crude oil emulsions. We evaluated the emulsion's rheological properties using various techniques, including rheometers, droplet size analysis, and interfacial force tensiometry. The results indicate that adding Ca²⁺ ions enhances the stiffness of water-oil emulsions, as evidenced by increased viscosity and reduced interfacial tension (IFT), which is attributed to interactions with acids rather than asphaltenes. Molecular dynamics (MD) simulations were performed to investigate the role of Ca²⁺ ions at the water-oil interface using a multicomponent crude oil model. The simulations revealed strong, specific interactions between Ca²⁺ ions and the organic acids in crude oil, leading to a significant reduction in IFT. These surface-specific interactions are identified as the source of increased stiffness in water-oil emulsion. These findings offer insights into the mechanisms that influence the properties of crude oil emulsions in the presence of Ca²⁺.