Carbonated smart water injection (CSWI) is a potential hybrid EOR technology under development. The process involves dissolving CO2 in smart water ripping the benefits of the synergic effect of CO2 injection and smart water. Based on the experimental laboratory data, including core flood experiments, this paper presents numerical investigations of the combined impact of dissolving carbon dioxide (CO2) in smart water (SW) on oil recovery in carbonate cores. An advanced processes reservoir simulator was utilized to build a core-scale model. Both the physics of smart water flooding as well as CO2-gas injection were captured. The generated model was validated against the coreflooding experimental data on hybrid CSWI, including cumulative oil production (cc) and oil recovery factor (). The Corey's correlation relative permeability model was used for capturing the multiphase flow. The numerical model was used to understand the underlying recovery mechanisms and crude oil-brine-rock interactions during CSWI. The model was further utilized to perform sensitivity analysis of different parameters and to optimize the CSWI design. Based on the numerical results, the experimental coreflooding data were accurately history-matched using the proposed model with a minimal error of 8.79 applying the PSO-based optimization method. Moreover, this history-matched model was further used for sensitivity analysis and optimization of the CSWI process. The objective functions for sensitivity analysis and optimization are based on minimizing the history-matching global error and maximizing oil recovery. The optimized design was achieved by performing a sensitivity analysis of various input parameters such as oil and water saturations (Soi and Swi), DTRAP (i.e., relative permeability interpolation parameter). On the other hand, in terms of maximizing the oil recovery while minimizing the usage of injected CSW solutions during CSWI, the optimal solution via the PSO-based approach achieved a cumulative oil recovery of 55.5. The main mechanism behind additional oil recovery with CSW is due mainly to wettability alteration and ion exchange between rock and brine. Additionally, CSWI was found to be more efficient in releasing trapped oil compared to waterflooding, indicating the synergic effect of dissolved CO2 in SW solutions. Based on this research, the envelope of CSWI application in carbonates for CO2-storage is expected to expand. This study presents one of the few works on numerical modeling of the CSWI process and capturing its effects on oil recovery. The optimized core-scale model can be further used as a base to build a field-scale model. This promising hybrid CSWI process under optimum conditions is expected to be economical and environmentally acceptable, which promotes future field projects. Copyright © 2023, Society of Petroleum Engineers.