Which One Is More Important in Chemical Flooding for Enhanced Court Heavy Oil Recovery, Lowering Interfacial Tension or Reducing Water Mobility?

A total of 33 sandpack flood tests were carried out to investigate the effects of interfacial tension (IFT) and water-phase viscosity on enhanced heavy oil recovery by chemical flooding. The amount of oil recovered by alkaline-only flooding increased sharply with the NaOH concentration in the range of 0.3-0.5 wt %. The oil recovery only varied slightly with the changing alkaline concentration outside the range. The coexistence of the surfactant and NaOH reduced the IFT between the oil and aqueous phase to an ultra-low level. However, the amount of oil recovered by alkaline/surfactant flooding only increased slightly with an increasing NaOH concentration up to a threshold value of 0.5 wt %. Beyond this threshold value, the recovery efficiency stopped increasing with the alkaline concentration and its value was lower than that of the alkaline-only displacing process. The addition of a polymer improved the tertiary oil recovery by increasing the viscosity of the water phase, although it also increased the IFT slightly. The combination of alkaline with polymer was more effective than polymer only upon enhancing the tertiary oil recovery. Comparing the results of tertiary oil recovery shows that the tertiary oil recovery of Court oil is correlated better with water-phase viscosity than IFT; i.e., increasing the viscosity of the water phase is more effective than lowering IFT in improving the tertiary oil recovery.