Experimental evaluation of smart water flooding in heterogeneous carbonate reservoirs under high pressure and high temperature for enhanced oil recovery

Smart-water flooding has emerged as a promising enhanced oil recovery (EOR) technique for improving oil production from heterogeneous carbonate reservoirs. This study experimentally evaluates engineered smart-brine injection using five carbonate core plugs from the WQ1-57 oilfield under high-pressure and high-temperature (HPHT) conditions. Three flooding scenarios were investigated sequentially: formation-water flooding, treated-water flooding, and engineered smart-water flooding. Core-flooding experiments were performed to evaluate cumulative oil recovery, differential pressure (ΔP), relative permeability, and effluent-ion behavior. Formation-water flooding produced oil recovery factors ranging from 31.7% to 50.4% OOIP, which increased to 41.2%-57.1% OOIP after treated-water injection and further improved to 47.2%-65.0% OOIP following smart-water flooding, corresponding to an incremental recovery of 16.8–28.9% OOIP over the formation-water case. Relative permeability analysis demonstrated a shift toward more water-wet conditions, accompanied by lower residual oil saturation and improved water-flow characteristics. Effluent-ion analysis confirmed the participation of Ca²⁺, Mg²⁺, and SO₄²⁻ in fluid-rock interactions responsible for wettability alteration. The results also indicated that the tested cores exhibited pronounced permeability heterogeneity (17–1020 mD) compared with the relatively narrow porosity range (19.4–29.3%), resulting in differences in flow behavior and recovery response. The observed recovery improvement demonstrates the potential of engineered smart-water flooding under the investigated HPHT laboratory conditions. Further reservoir-specific investigation, numerical simulation, economic assessment, and pilot-scale validation are required before field implementation.