Investigation of the Synergistic Effects of Different Salts in Smart Water Injection Fluids on Oil-Brine Interfacial Tension.

Although the need for an energy transition is increasingly evident, fossil fuels will remain essential for humanity, highlighting the necessity for responsible migration strategies. In this context, low-salinity injection methods enable smart management of oil production while addressing the United Nations Sustainable Development Goals (SDG 7) in the 2030 Agenda. These methods reduce the environmental impact of oil production while ensuring the continuation of fossil fuel extraction necessary for social well-being in the coming decades. Despite the absence of consensus on the optimal saline composition and concentrations in smart water, its effectiveness is largely linked to changes in wettability and reductions in interfacial tension (IFT) within the oil-brine-rock system. This study explores the synergistic effects of sodium chloride, calcium chloride, and sodium bicarbonate across two total dissolved solids ranges (0-70,295 mg/L and 2200-24,813 mg/L) on IFT with Brazilian presalt oil, comparing the results with oil recovery factors obtained from carbonate rock tests. The findings indicate that salinity significantly influences the individual effects of each salt on IFT. In high-salinity scenarios, the presence of CaCl2 notably increases IFT with oil, suggesting that the bilayer effect between Ca2+ ions and organic acids predominates. Conversely, at low salinity, NaCl demonstrated the most significant impact in reducing the IFT, indicating that the salting-in phenomenon prevails. The most pronounced synergistic effects occurred between CaCl2 and NaHCO3 in high-salinity environments and between NaCl and NaHCO3 in low-salinity situations. In both cases, the interference was positive, suggesting that the deprotonation of organic acids facilitated by the basic salt does not aid in lowering the IFT when combined with other salts. However, in high-salinity environments, NaHCO3 exhibited negative interference but contributed to a reduction in IFT. A correlation was observed between the decrease in the IFT and an increase in the oil recovery factor, particularly under conditions with high NaCl concentrations and low to medium levels of CaCl2 and NaHCO3.