Assessing the Effect of Carbonated Water Injection Compared to Low Salinity Water Injection on Oil Recovery in Water Wet Sandstones as a CCUS Method

High Resolution Image Download MS PowerPoint Slide This study evaluates the performance of carbonated water flooding compared to noncarbonated water injection in sandstone systems with contrasting mineralogy and permeability. The objective was to identify the governing recovery mechanisms and assess whether carbonated water can enhance oil recovery through wettability alteration or CO 2 -induced oil swelling under controlled conditions. A structured experimental workflow was applied, including spontaneous imbibition to quantify capillary forces and initial wettability, surface reactivity tests to evaluate mineral–brine interactions, CO 2 solubility and mass transfer measurements, and PVT simulations to analyze phase behavior and fluid properties. Viscous core flooding experiments were then conducted at 60 °C and 80 bar to compare recovery performance of carbonated and noncarbonated brines. The results show that both sandstone systems remained strongly water-wet after restoration with oil recovery primarily governed by capillary forces. Carbonated water did not induce measurable wettability alteration, and low-salinity injection did not provide additional recovery. The CO 2 solubility in the brine and its transfer to the oil phase were limited, resulting in negligible changes in oil viscosity, density, or swelling behavior. In high-permeability quartz-dominated cores, carbonated water yielded a slightly higher recovery, although the difference was minor. In contrast, in lower-permeability cores, carbonated water resulted in slightly lower recovery, likely due to increased sensitivity to displacement efficiency in tighter pore systems without any compensating mechanism from CO 2 . These findings indicate that carbonated water does not introduce a dominant EOR mechanism under strongly water-wet conditions. However, its recovery performance remains comparable to that of conventional flooding while enabling simultaneous CO 2 injection. This makes carbonated water a relevant strategy for integrated oil recovery and subsurface CO 2 storage, particularly where the storage potential is of interest beyond incremental recovery.