Effects of viscosification, ultra-low interfacial tension, and emulsification on heavy oil recovery by combination flooding

Abstract

Heavy oil recovery mechanisms by combination flooding have well recognized as viscosification, ultra-low interface tension (IFT) and emulsification, however, the role or relative contribution of each mechanism to oil recovery is still not clear (especially under different water-oil viscosity ratios). To address this, two emulsified and one ultra-low IFT mixtures were collected and systematically compared in their IFT, emulsion stability and oil recovery performances. The results show that, as excepted, the used formulas have different IFT and emulsion stability properties: for the ultra-low IFT one, IFT indeed reaches an ultra-low level, but the stability of its emulsion is very poor. The emulsified formulas (with non-ultra-low, ultra-low IFT) are more powerful in stabilizing heavy oil emulsion than the former. Significant discrepancy in combination flooding under different viscosity ratios in homogeneous and heterogeneous models reveals that: when the viscosity ratio is lower than 0.2, the mobility control by the combination mixture is insufficient, and the contribution of emulsification is relatively high (6.4–24.0 %), the dominant oil recovery mechanism is the synergy of those three mechanisms. As the viscosity ratio gets higher than 0.2, the mobility control is strong, resultingly, the contribution of emulsification is reduced, making it less important. In addition, although the presence of heterogeneity does not change the critical value of viscosity ratio, it has a significant impact on the detailed contribution of the dominant mechanisms.