Impact of Low Salinity Water Injection on CO2 Storage and Oil Recovery for Improved CO2 Utilization

Abstract

CO2 utilization for oil recovery applications is often impacted by the challenges such as viscous fingering and its premature breakthrough. Injection of slugs of water-alternating-gas (WAG) generally aims to overcome these challenges though the control of CO2 mobility. Moreover, the oil recovery potential of WAG is largely dependent on the injection water salinity and the subsequent CO2 dissolution and storage. Therefore, the effect of varying salinity (0–4 wt% NaCl) on CO2 loading capacity of water is investigated in this study, at two test temperatures of 323 K and 363 K and three confining pressures of 4, 8, and 12 bar, and subsequently, the flooding experiments were performed to find the low salinity (LS)-WAG process suitability in oil recovery applications from porous sandstone rocks. The inclusion of salt was found to significantly affect CO2 loading capacity of water. At higher NaCl concentration (4 wt%), CO2 loading decreased by 50% as demonstrated by absorption kinetic study. LS-WAG suggested maximum oil recovery 55–58% of original oil in place for water salinity of 2 wt% NaCl at both the test temperatures. Increment in pressure had a positive impact on CO2 loading while increasing temperature showed reverse behavior. As a result of LS in WAG and kinetic adsorption study, it is anticipated that the reduction in water salinity is a favorable factor in the CO2 storage and oil recovery performance of CO2 injection. The instance of CO2 injection was also varied for LS-WAG process and its effect on oil recovery from sand-packs was reported. Oil recovery results demonstrated that WAG was similarly effective in all the stages of the injection cycle as long as water salinity remained lower than 2 wt% NaCl. Based on the findings in this study, it is recommended to implement the WAG in conjunction with low salinity water (LSW) in moderate saline conditions, which is of key importance for various applications where water salinity differs on a large scale.