Enhancing Oil Recovery in Carbonate Reservoirs Through Low Salinity Waterflooding: Laboratory Insights, Smart Brine Optimization, and Field-Scale Validation

Abstract Objectives/Scope This study aims to evaluate the effectiveness of Low Salinity Waterflooding (LSWF) in enhancing oil recovery from carbonate reservoirs. It investigates wettability alteration mechanisms through laboratory analyses, including imbibition tests, zeta potential, and contact angle measurements. The study also optimizes smart brine formulations—particularly sulphate-enriched variants—and validates findings through core flooding and field-scale reservoir simulations, providing a comprehensive assessment for broader application. Methods, Procedures, Process The study employed a multi-scale approach combining laboratory experiments and field-scale simulations. Laboratory methods included spontaneous and sequential imbibition tests, zeta potential analysis, contact angle measurements, and rock-fluid compatibility assessments to understand wettability alteration mechanisms. Core flooding experiments identified the optimal salinity and evaluated various smart brine formulations, particularly sulfate-enriched solutions. Compatibility tests ensured injectivity and formation integrity. These findings were further validated through numerical core flood simulations and field-scale reservoir modelling. A pilot test in Field H provided real-world performance data, enabling direct comparison with non-LSWF areas to assess incremental oil recovery. Results, Observations, Conclusions The study demonstrated that Low Salinity Waterflooding (LSWF) significantly enhances oil recovery in carbonate reservoirs by altering rock wettability. Laboratory experiments showed a reduction in residual oil saturation by 18.8 saturation units when compared to conventional seawater flooding. Zeta potential measurements indicated increasingly negative values with decreasing salinity and elevated sulphate ion concentration, suggesting enhanced electrostatic repulsion between oil and rock surfaces, facilitating oil detachment. Core flooding identified 25% diluted seawater as the optimal salinity, while sulfate-enriched smart brines yielded an additional 3.19% recovery over standard LSWF. In contrast, calcium- and magnesium-enriched brines had minimal impact. Compatibility tests confirmed the suitability of diluted seawater for injection, minimizing scaling risks. Field-scale simulations projected an incremental oil recovery of 0.86 MMt, representing a 2.9% increase in total production. Early pilot data from Field H showed reduced oil decline rates and stabilized water cut, reinforcing laboratory and simulation findings. These results validate the effectiveness of sulfate-enriched LSWF and support its broader application in similar carbonate reservoirs, with careful optimization of sulfate levels recommended to balance recovery and formation integrity. Novel/Additive Information This study provides novel insights into the application of sulfate-enriched low salinity waterflooding (LSWF) in carbonate reservoirs, integrating laboratory mechanisms with field-scale validation. Unlike previous studies, it identifies optimal salinity and sulphate concentrations, quantifies their effect on wettability and oil recovery, and demonstrates real-world performance through a field pilot. This holistic approach bridges lab-to-field knowledge gaps, offering practical guidance for EOR implementation.