Intermittent CO2 and viscosity-reducing gas (VRG) injection for enhanced heavy oil recovery

Abstract

The results of three coreflood experiments are reported which were performed to investigate intermittent CO2 and viscosity-reducing gas (VRG) injection for enhanced heavy oil recovery (EHOR). This injection strategy is particularly suitable for heavy and viscous oil reservoirs as it enhances the contact between the resident oil and injected fluid. The recovery efficiency of continuous injection is low due to the high viscosity ratio between the oil and injection fluid. The intermittent injection of liquid CO2 for 4cycles resulted in the recovery of 12% of the initial oil in place (IOIP) while in the second experiment, 9cycles of intermittent supercritical CO2 injection recovered 38% IOIP. In the third experiment, 5cycles of intermittent VRG injection led to the recovery of 22% IOIP. The results demonstrate that a higher quality oil than the original oil in the core is recovered during the periods of CO2 and VRG injection. However, it is shown that different mechanisms were contributing to oil recovery during CO2 and VRG injection. The results of the simulation study imply that the mechanism of extraction of hydrocarbons by CO2 would be an important reason for the recovery of higher quality oil during the periods of CO2 injection whereas its impact is less pronounced when the injection gas is a hydrocarbon gas. However, the extraction of hydrocarbons to the CO2-rich phase could not be fully responsible for the higher quality oil recovery and it is discussed that how this mechanism could affect the flow of CO2 and oil in porous media.