Experimental investigation of wettability alteration from water-wet to oil-wet during oil migration

Most oil reservoirs are first saturated with water and become oil-wet gradually due to oil migration and accumulation. Previous studies reported that the adsorption of hydrocarbon components onto the rock surface during a considerable time caused wettability alteration from primarily water-wet to oil-wet. However, few studies fundamentally reviewed the effects of the ionic composition of formation water on the process of the rock surface wettability alteration from water-wet to oil-wet using advanced surface analysis tools. In this research, wettability alteration of calcite surface from water-wet to oil-wet and (in the next step) from oil-wet to water-wet was studied using a specific carboxylic acid (stearic acid), normal decane, and three single salt aqueous phases. During this research, the surface was analyzed using contact angle and scanning electronic microscopy. Results showed that using deionized water as an aqueous phase caused maximum surface adsorption of carboxylic components and minimum adsorption occurred in the presence of the MgCl₂ aqueous phase. The carboxylic acid adsorption onto the calcite surface was controlled by interactions of negative ions formed during dissociation of carboxylic acids and positive salt ions present in brine solvents.