Effect of the Type and Concentration of Salt on Production Efficiency in Smart Water Injection into Carbonate Oil Reservoir Rocks

Smart waterflooding is one of the most practical emergingmethodsof enhanced oil recovery in carbonate reservoirs. In this study, theeffect of salt type and its concentration in smart water on oil recoveryfrom a carbonate reservoir rock is investigated. A series of experimentalmeasurements, including zeta potential (ZP), interfacial tension (IFT),and contact angle (CA), were conducted to examine the effect of ionson the oil/brine/rock interaction. IFT, ZP, and CA were also usedas screening methods to select effective solutions for flooding experiments.The results of the study show that synthesized brines containing sodiumacetate and potassium acetate salts have a significant effect on thereduction of IFT; however, rock surface wettability due to such brinesis insignificant. The presence of organic salts in the injected watercan alter the properties of the fluid and rock surface, leading toimproved oil recovery. The salts can reduce the interfacial tensionbetween the oil and water phases, making it easier for the water todisplace and mobilize trapped oil. This effect is particularly beneficialin reservoirs with high oil-water interfacial tension as itenhances the capillary forces and improves the sweep efficiency. Smartwater with sodium acetate (MSW.NaOAc) caused a 7% increase in oilproduction in the tertiary injection process due to IFT and CA reduction.The secondary injection of MSW.NaOAc led to an oil production efficiencyof 76%, which is 10% higher than that of the secondary injection ofseawater (SW), confirming the effectiveness of acetate ions in enhancingoil recovery. Doubling the concentration of sulfate ions in modifiedSW (MSW.NaOAc.2S) caused a 19% increase in oil production in tertiaryinjections after SW flooding. The secondary injection of MSW.NaOAc.2Sproduced a 13% increase in the recovery factor compared to SW floodingin the secondary mode. The main driving mechanism for oil mobilizationwas found to be wettability alteration, which is supported by theanalyses of CA and ZP. This study confirms that the salt type andconcentration present in a brine solution play a vital role in themovement of trapped oil in carbonate reservoirs.