Insight into the mechanism for oil recovery using EDTA chelating agent solutions from clayey sandstone rocks

Recently, EDTA chelating agent solutions were proposed as a new chemical enhanced oil recovery (CEOR) technique. The intention of this work is to address the possible mechanism or mechanisms responsible for enhancing oil recovery from clayey sandstone core samples. The stability of the EDTA at high temperature and high pH was studied. Interfacial tension (IFT) measurements, zeta-potential measurements, and coreflood experiments were conducted to understand the recovery mechanism leading to the additional oil recovery after the conventional seawater flooding. The produced effluents from the coreflood experiments were analyzed for ion composition, and their pH was measured. The ability of the EDTA to restrain the reactivity of different cations, especially Ca⁺² and Fe⁺³, toward other species was found to be the most important characteristic of EDTA to increase the oil recovery by introducing the possibility of increasing the injected brine pH. The EDTA solutions prepared in synthetic Arabian Gulf seawater (SSW) at high pH were capable of releasing the adsorbed acidic and basic crude oil particles from the clays surfaces rendering the surface of the sandstone rock more water-wet.