Effect of in-situ emulsification of surfactant on the enhanced oil recovery in low-permeability reservoirs

Abstract

Surfactant flooding technology has become an important treatment for the enhance oil recovery (EOR) in low-permeability reservoirs, and which behavior of surfactant is more important for EOR, lowering interfacial tension (IFT) or in-situ emulsification, is still debatable. In this work, to ascertain the dominating behavior of surfactant, a series of comparative experiments were performed to observe their dynamic flooding performances in artificial cores over a permeability range between 5 mD and 50 mD. Besides, a 2D heterogeneous model was used to explore the effect of micro heterogeneity on surfactant flooding. At last, the adaptable limits, including heterogeneous degree and injective time, were further discussed. The results show, the overall oil recovery increases with permeability, while their flooding dynamics also changes with permeability. The results show, in-situ emulsification of surfactant plays the key role in oil recovery compared with IFT reduction, especially with the cores’ permeability decreasing. On the one hand, the strong emulsifying capability of surfactant is advantageous in dispersing the residual oil to reduce oil saturation. On the other hand, the formation of amounts of emulsion droplets is useful to block the pore and further contributes to establish pressure variation and delaying water-cut raising. Meanwhile, strong emulsifying capacity of surfactant is positive to improve the swept efficiency in micro heterogeneous distributions and avoid the formation of micro water channel. Lastly, the adaptable conditions tests indicate the extremely strong heterogeneity and low crude oil saturation are the crucial factor to affect the EOR performances owing to the ease of in-situ emulsification formation. Therefore, this finding of this study can help for better understanding of contribution of in-situ emulsification of surfactant for EOR and its limitations in low-permeability reservoirs, which could be a candidate with great potentials for field application and economic returns.