Smart-water enhanced oil recovery in carbonate reservoirs: experimental validation, 3D numerical modeling, and optimization

Heterogeneous carbonate reservoirs exhibit complex flow behavior, strong wettability variations, and early water breakthrough, which limit the efficiency of conventional water flooding and reduce oil recovery. Smart-water injection has emerged as a promising enhanced oil recovery (EOR) technique; however, its field-scale application remains challenging due to uncertainties associated with ion composition, reservoir heterogeneity, and injection strategies. This study develops an integrated multi-scale workflow that combines smart-water laboratory experiments, core-scale validation, 3D reservoir simulation, uncertainty quantification, and optimization to evaluate and maximize smart-water performance in the WQ1-57 carbonate reservoir. Experimental investigations demonstrate that engineered brines enriched with optimized concentrations of sulfate (SO₄ 2 ⁻), calcium (Ca 2 ⁺), and magnesium (Mg 2 ⁺) ions promote wettability alteration toward more water-wet conditions, resulting in incremental oil recovery of 11.7–22.8% at core scale. A calibrated numerical model was developed using the MATLAB Reservoir Simulation Toolbox (MRST) and validated through history matching before being upscaled to reservoir scale. Simulation results reveal that smart-water injection can achieve up to 18.0% incremental oil recovery, delay water breakthrough by 0.1–0.3 pore volume (PV), and improve areal and vertical sweep efficiencies by up to 14% and 20%, respectively. Sensitivity analysis identifies horizontal permeability, sulfate concentration, and injection pattern as the dominant controlling parameters, contributing up to 18%, 12%, and 14% variations in recovery performance. Monte Carlo uncertainty analysis confirms the robustness of the proposed approach, with predicted recovery factors ranging from 32.8% to 55.3% (mean value: 46.4%) and incremental recovery ranging from 6.1% to 12.8% under P90-P10 uncertainty scenarios. The optimization framework further identifies that horizontal production wells combined with layered conformance-controlled smart-water injection provide the optimum development strategy, achieving a maximum incremental recovery of 18.1%. The novelty of this work lies in integrating experimental ion optimization, uncertainty-aware reservoir simulation, and intelligent injection optimization within a single workflow, providing a scalable methodology for designing robust smart-water EOR strategies in heterogeneous carbonate reservoirs.