Impact of injected water salinity on CO2 storage efficiency in homogenous reservoirs

Abstract

Water alternating gas (WAG) injection significantly improves enhanced oil recovery efficiency by improving the sweep efficiency. However, the impact of injected water salinity during WAG injection on CO2 storage efficiency has not been previously demonstrated. Thus, a 3D reservoir model has been developed for simulating CO2 injection and storage processes in homogeneous reservoirs with different water injection scenarios (i.e. low salinity water injection (1000 ppm NaCl), high salinity water injection (250 000 ppm NaCl) and no water injection), and the associated reservoir-scale CO2 plume dynamics and CO2 dissolution have been predicted. Furthermore, in this work, we have investigated the efficiency of dissolution trapping with and without WAG injection. For all water injection scenarios, 5000 kton of CO2 were injected during a 10-year CO2 injection period. For high and low salinity water injection scenarios, 5 cycles of CO2 injection (each cycle is one year) at a rate of 1000 kton/year were carried out, and each CO2 cycle was followed by a one year water injection at a rate of 0.015 pore volume per year. This injection period was followed by a 500-year post injection (storage) period. Our results clearly indicate that injected water salinity has a significant impact on the quantity of dissolved CO2 and on the CO2 plume dynamics. The low salinity water injection resulted in the maximum CO2 dissolution and minimum vertical migration of CO2. Also, our results show that WAG injection enhances dissolution trapping and reduces CO2 leakage risk for both injected water salinities. Thus, we conclude that the low salinity water injection improves CO2 storage efficiency.