Effects of cation salinity on the dynamic interfacial tension and viscoelasticity of a water-oil system

This experimental study aims to obtain insights into the effect of brine salinity on the dynamic interfacial tension (IFT) and interfacial behavior of a water-oil system. The effects of monovalent and divalent cations (Na⁺, Ca²⁺, and Mg²⁺) in a salinity range of 0.01–0.1 mol/l on the equilibrium and dynamic interfacial tension of the water-oil system are studied using pendant drop experiments. To understand the adsorbed layer of surface active components (asphaltene and resin) at the interface, surface dilational elasticity is also studied. The results reveal that the types of the ions, salinity concentration, and type of the surface-active components in the crude oil, are dominant parameters that affect the interfacial properties. Divalent cations especially Mg²⁺ show a much stronger interaction with surface-active components at the brine-oil interface while monovalent cations have a negligible effect. The IFT of the water-oil system decreases in the presence of salts up to a minimum point and a further increase in the salinity leads to an increment in the IFT. The effect of salinity on the formation of asphaltene and resin components at the drop surface is studied by employing surface area compression experiments. When asphaltene components are at the interface, the drop profile shows a sharp increase in standard deviation from Laplacian form at the closely-packed state, while for maltene (deasphalted oil), no rise is observed in the standard deviation values. The closely-packed state and the asphaltene layer collapse happen at an earlier time with increasing salt concentration up to an optimum point due to the presence of the higher amount of complexes at the interface.