CO2 Injection in heavy oil reservoirs improves oil recovery and at the same time may reduce some of the environmental concerns associated with heavy oil recovery by thermal methods. Depending on the reservoir conditions and oil properties, 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 challenge for application of CO2 in heavy oil reservoirs. Therefore, CO2 injection needs to be combined or augmented by other displacement mechanisms (e.g. waterflood, foam injection) to efficiently displace the heavy oil diluted with CO2. In our previous papers, the micro-scale displacement efficiency and mechanisms involved in CO2 and CO2-foam injection in heavy oil systems were investigated and presented through vivid micromodel images. This paper presents the results of a series of coreflood experiments performed to evaluate the potential of liquid-CO2 and CO2-emulsion injection in a heavy oil reservoir.
The coreflood results show a very good performance for CO2 injection. An ultimate recovery of around 70 %OOIP as a result of secondary and tertiary CO2 injection was achieved which was twice the recovery obtained by waterflood in this heavy crude oil. This substantial recovery improvement was a consequence of a massive viscosity reduction (up to 97.5% of the original oil viscosity) at reservoir conditions. Co-injection of liquid CO2 and a selected surfactant also resulted in in-situ formation of a very stable CO2-emulsion which reduced mobility of injected CO2 by three orders of magnitude in presence of oil. In-situ generation of CO2-emulsion as evident from an increased in the pressure drop across the core was observed even at high oil saturation of up to 50%. The results of this work show significant potentials for immiscible CO2 and CO2-emulsion injection as an effective enhanced heavy oil recovery technique.