Laboratory Investigation of Oil API Degree Effect during Carbonated Water Injection and Comparison in Secondary and Tertiary Injection

Carbonated water (CO2 saturated water) injection is one of the enhanced oil recovery methods that during this process, CO2 without forming a new phase transfers from the aqueous phase to the oil phase. Due to the higher solubility of CO2 in oil phase compare to the aqueous phase (at the same temperature and pressure), CO2 migrates from water to oil phase and because of CO2 dissolution, oil viscosity decreases and oil swells which will be effected the ultimate oil recovery. Few studies have investigated the effect of oil API in secondary and tertiary carbonated water injection in compacted sandstone. In this study, the core flooding experiments were performed at the reservoir temperature and pressure with one of Iran oil reservoirs to investigate the effect of oil API on the oil recovery. Based on the results, with API decreasing and viscosity increasing, the ultimate recovery in both carbonated water and saline water injection was decreased but in carbonated water injection because of improving oil mobility compare to injected fluid, the performance of carbonated water injection increased. Therefore, if the injection is performed as the secondary injection, the oil recovery rate will be higher than the tertiary injection. Also higher oil API numbers cause more difference between the recovery of carbonated water and saline water that represents the priority of carbonated water injection in the heavy oil reservoir.