Spontaneous imbibition is known as one of the main recovery driving forces in naturally fractured reservoirs. In this study, a numerical model to investigate the impact of carbonated water on oil recovery during spontaneous countercurrent imbibition is presented. This model includes the dynamic modification of oil viscosity, oil swelling, wettability, and interfacial tension. The results show that the injection of carbonated (CO2-enriched) water can improve water spontaneous imbibition rates as the system goes toward a more water-wet condition. The tertiary process also becomes more efficient as the remaining oil viscosity decreases. The results show that using the same relative permeability and capillary pressure data for simulation of both water and carbonated water displacements yields the system more quickly reaching the residual oil saturation in the carbonated water case, however, with the same ultimate oil recovery compared to that of the water case.