Effect of permeability on displacement efficiency and dominant oil–displacement mechanism in surfactant flooding

Abstract

Interfacial tension (IFT) reduction and emulsification are two important mechanisms of surfactant flooding. However, for light oil reservoirs with different permeabilities, whether which mechanism is more important in improving displacement efficiency remains unclear. In this study, surfactants with strong emulsifying properties and ultralow IFT were screened using an interfacial tensiometer and a self-developed emulsification performance tester. The ability of the two surfactants to improve displacement efficiency was compared through a series of core flooding experiments. Experimental results showed that the surfactant with ultralow IFT did not have strong emulsifying properties. With the decrease in permeability, the oil displacement efficiency improved by emulsification increased first and then decreased, whilst that improved by IFT reduction declined. Moreover, IFT reduction was the dominant mechanism to improve oil displacement efficiency in medium-high and ultralow permeability reservoirs, whilst emulsification was dominant in low permeability reservoirs. The comprehensive utilization of multiple mechanisms and the combination of technologies should be considered when surfactant flooding is used in reservoirs with ultralow permeability. This work advances our current understanding of surfactant flooding and provides a reference for the formulation of plans to enhance oil recovery in light oil reservoirs.