Surfactants effect on the oil/water/rock interface behavior recent study progress

Surfactant-enhanced oil recovery was an important technical direction for chemical enhanced oil recovery. It lowered the threshold for residual oil after water flooding and improved the micro-displacement efficiency and macro-development effects of complex reservoirs, which could be used to regulate the oil/water and oil/solid interface multiphase flow behavior. When the conventional reservoirs entered high water cut or recovery stages, the residual oil would gradually transformed from a continuous oil phase into the non-contiguous pore corner oil. But the residual oil flow was jointly limited by capillary pressure, rock surface adhesion, crude polar component aggregation, and interfacial film stability, and many methods (surfactants, polymers, ect) could be used to enhance the process. Among these methods, surfactants can be directionally adsorbed onto the oil-water interface to reduce the interface free energy, thus promoting the deformation, peeling and migration of oil droplets. At the same time, surfactants can form competitive adsorption layers or hydration films on the rock surface, altering the minerals suface wettability and chargeability. Additionally, surfactants can improve the crude oil mobility through emulsification and microemulsification‌. This paper reviewed the surfactant interfacial behavior onto the oil-water–rock interface, the surfactants species were analyzed, and the structural characteristics, interfacial interactions and reservoir suitability were analyzed. Surfactants could be divided into the cationic, anionic, non-ionic, and zwitterionic surfactant. Different surfactants had the different property onto the interface modification. The different surfactants application should mainly be limited to certain carbonate rock reservoirs, special surface electrical conditions, or composite systems modified by nonionic, amphoteric, and low-adsorption structures. This paper further clarifies the mechanisms of surfactant-intensified oil extraction, mainly focusing on processes such as reduced interfacial tension, changes in wetting properties, emulsification and formation of microemulsions, competition between adsorption and desorption, reconstruction of interfacial films, and transport of pore-scale dimensions. It also provides a detailed analysis of the effects of mineralization, divalent ions, temperature, pressure, rock mineral composition, and heavy crude oil components on interface behavior. In view of the current challenge in research, such as adsorption losses, degradation at high temperatures, sedimentation at high-salinity, uncontrolled emulsification, blockages in pores and throats, high difficulty in geological processing, cost constraints, and significant environmental risks, this paper proposes a multi-scale coupled assessment method that couples with molecular simulations, microfluidics, and core displacement experiments, and incorporates AI-assisted formulation screening to systematically evaluate the sustained release performance of green surfactants, intelligent response composite systems, and nanocarrier fluids. At the same time, this paper provides a theoretical basis for molecular design, interface regulation, and engineering application of surfactant systems in complex reservoirs.