Experimental Investigation of CO2, CO2SWAG and CO2-Foam Injection Scenarios for Enhanced Heavy Oil Recovery

In heavy oil reservoir, CO2 does not develop miscibility but it can substantially reduce the oil viscosity by dissolving in the oil and hence, improve recovery factor. Viscosity reductions of up to two orders of magnitude may be achieved as a result of CO2 dissolution in heavy oil. However, adverse viscosity ratio which results in viscous fingering and early breakthrough of CO2 is a constraint for application of CO2 injection in heavy oil reservoirs. In addition, in the case of thin reservoirs (horizontal displacement) gravity segregation results in gravity override which further reduces the sweep efficiency. As a result, CO2 injection requires be combining with either water flood or injecting in the form of CO2-foam in order to have acceptable sweep efficiency in viscous and heavy oil reservoirs. In our previous papers, the displacement efficiency in waterflood, CO2 and CO2-foam injection in heavy oil systems under gravity stable condition were investigated. This paper presents the results of a series of coreflood experiments performed to evaluate the potential of water, CO2, CO2SWAG and CO2-foam injection in a heavy oil reservoir under condition of gravity segregation. This paper presents the results of a series of coreflood experiments performed in order to evaluate the potential of different water and CO2 injection strategies for improving heavy oil recovery. CO2 injection showed great potentials for increasing oil recovery when it was injected in secondary mode and an ultimate recovery of around 45 %IOIP was achieved. Compared to water flood, secondary CO2 injection recovered much more oil especially after breakthrough. Combining CO2 and water injection by simultaneously injecting CO2 and water (CO2SWAG) increased oil recovery more that only water or only CO2 injection. CO2SWAG reduced the CO2 mobility and increased sweep efficiency and a final recovery of 70 %IOIP accomplished. The addition of an appropriate surfactant to the flood water and its co-injection with CO2 resulted in the in-situ formation of CO2-foam which provided better mobility control and resulted in the highest oil recovery amongst the injection strategies tested. The differential pressure across the core significantly increased during the co-injection of CO2 and the surfactant solution which was a strong indication of in-situ formation of CO2-foam even at high oil saturation of up to 60%.