A review on retention of surfactants in enhanced oil recovery: A mechanistic insight

In mature reservoirs, over 60% of oil remains trapped after waterflooding and can only be recovered using enhanced oil recovery (EOR) methods, including chemical EOR. Surfactants are one of the main components of the chemical formulations used for chemical enhanced oil recovery (CEOR) processes. Despite the great success in developing superior chemistries of surfactants for high efficiency in even harsh conditions, the adsorption of surfactants is still a significant challenge the industry faces today. Loss of surfactants leads to inadequate performance and poor oil recovery efficiency; consequently, the management and control of surfactant retention are highly researched in academia and industry. Surfactant adsorption follows several mechanisms, and understanding these mechanisms is key to effectively controlling their retention in CEOR processes. This review focuses on the various mechanisms of surfactant adsorption onto different rock types and minerals encountered in reservoirs. The effect of several parameters on adsorption, such as surfactant structure, temperature, brine composition, and surface properties, is discussed in detail. As CEOR requires combinations of surfactants in applications, the adsorption behavior of surfactant mixtures is also well elaborated. In addition, the review covers recent trends in mitigating surfactant adsorption, such as using sacrificial agents, alkalis, low-salinity brine, nanoparticles, and ionic liquids. Furthermore, schemes for adsorption control, such as low salinity preflush and negative salinity gradient, are discussed. Overall, this review aims to provide a comprehensive understanding of surfactant adsorption behavior and mitigation techniques to improve the efficiency of CEOR processes.