Individual and Symbiotic Interfacial Contribution of Ions to Hydrophilic Enhancement of Oil-Bearing Dolomite: Implication to Ion-Engineered Waterflooding

Abstract

The ion-specificity of minerals' wettability is an active research area of particular importance in ion-engineered waterflooding as a promising enhanced oil recovery method. In this process, the wettability of the oil-brine-rock (OBR) system is changed by designing the ions of injected water. Though the contribution of ions to the wetting character of carbonates, particularly dolomite (CaMg(CO3)2), has been investigated by various studies, the contribution of ions still needs to be resolved. Through a systematic experimental investigation, the present paper sheds light on the contribution of the main constituent ions of natural brines to retrieving the water-favoring virtue of oil-bearing rocks majorly composed of dolomite. The static wettability measurements showed distinct affinity of individual surface-active ions to the dolomite/water interface, following the order SO42- > NO3- > Ca2+ > Mg2+. To clarify the effect of mixed electrolytes, results of experimental scenarios showed the assisting role of sulfate and, to a lesser extent, nitrate to restore the hydrophilic virtue of oil-aged dolomite samples, irrespective of the divalent cations, which was also mirrored to incremental oil displacement upon enriching those anions in dynamic core flooding tests. The cooperation of SO42- and NO3- anions yielded optimal wettability alteration in static experiments and maximum oil mobilization in core flooding tests. Insights provided here improve our knowledge of the ion-dependent wettability response of dolomite with implications to diverse fields of surface science, particularly for the rational design of brine composition to acquire optimal performance of water-based EOR operations.