Water-saturated CO2 injection to improve oil recovery and CO2 storage

CO2 is injected into oil reservoirs to improve oil recovery and sequester greenhouse gas. However, the high mobility of CO2 leads to poor sweep efficiency; consequently, a large volume of oil in the reservoir is left behind, limiting the oil recovery and CO2 storage. This paper introduces water-saturated CO2 injection to improve oil recovery and CO2 storage by reducing the mobility of the CO2. Unlike carbonated water injection, in which the fluid is mostly water, the fluid in water-saturated CO2 injection is less than 1% water. Water-saturated CO2 injection and CO2 injection are compared experimentally using Bentheimer sandstone cores that contain oil. Oil recovery, pressure difference across the core, and compositions and rates of the produced fluids are recorded. The ultimate pressure difference across the core samples during water-saturated CO2 injection is found to be 4.76-9.55 times that the ultimate pressure difference during CO2 injection-indicating reduced CO2 mobility during water-saturated CO2 injection. To investigate the impact of this mobility reduction on oil recovery and CO2 storage, three-dimensional field-scale simulations are run. Simulations show that in the low permeable layer, the sweep efficiency during water-saturated CO2 injection exceeds that during CO2 injection. Consequently, the simulations find water-saturated CO2 injection to yield 7% higher oil recovery and 1.14 mega-tons additional CO2 stored than does CO2 injection.