A Systematic Study on the Impact of Surfactant Chain Length on Dynamic Interfacial Properties in Porous Media: Implications for Enhanced Oil Recovery

We propose a new systematic procedure to investigate the effect of hydrophobic and hydrophilic chain lengths of polyoxyethylenated (POE) nonionic surfactants on dynamic interfacial properties in porous media. We study the impact of nonionic surfactant structure on oil recovery through comprehensive experimental measurements of phase behavior, cloud point, dynamic interfacial tension, dynamic contact angle, and spontaneous and forced imbibitions at ambient and reservoir conditions. We identify a surfactant structure that increased the oil production by 22% and 6% compared to tap water and a nonionic surfactant commercially deployed in a major unconventional oil reservoir, respectively. In this work, we observe that factors such as minimum interfacial tension used for surfactant selection are not the only parameters influencing displacements at the pore scale. The results of this study reveal that when a surfactant solution imbibes into the pore space as an invading phase, the surfactant ability to lower the IFT and reach equilibrium faster plays an important role in the local trapping of oil phase on a pore-by-pore basis. We propose a mechanism relating this surfactant behavior to oil brine displacement and confirm our results by visual observation of in situ pore fluid occupancies after surfactant imbibition in micromodels and naturally occurring porous media.