The detachment of oil films from rock surfaces and the overall washing capability of injected fluids are fundamental mechanisms for improving oil recovery. A key factor influencing oil film removal is the ability to modify the wettability of reservoir rock. When a suitable surfactant formulation is injected into an oil reservoir, it creates a synergistic effect by simultaneously reducing interfacial tension and adjusting surface wettability.
The reduction of interfacial tension decreases the adhesion force of oil droplets on the mineral surface, which facilitates the detachment of residual oil films. Furthermore, modifying an oil-wet surface to a weakly water-wet state further supports this detachment process. The ease of oil film removal can be quantitatively characterized by measuring the underwater three-phase contact angle of oil on a solid surface. In laboratory evaluations, crude oil is deposited as a film or droplet onto substrates such as quartz, and the dynamic evolution of the contact angle is monitored using a contact angle meter. This method provides a reliable, quantitative assessment of a surfactant solution’s effectiveness in displacing crude oil.
The washing efficiency of a surfactant system is closely related to its ability to lower interfacial tension, alter wettability, and detach oil films. Research indicates that washing efficiency results from the combined influence of these factors. Through the use of micromodels, studies have demonstrated the enhanced recovery mechanisms of emulsifying surfactant systems. The findings indicate that emulsification contributes to improved oil recovery. At pore throats, the Jamin effect can lead to the formation of temporary emulsion droplet blockages. This selective plugging diverts the flow of subsequent injection fluid into unswept areas, improving macroscopic sweep efficiency through fluid diversion.
Investigations into interfacial mechanisms have identified how the anionic surfactant SDBS influences the wettability of reservoir rocks. Through interfacial modification, SDBS induces wettability alteration on minerals such as calcite, dolomite, and silica. Experimental data show that siliceous substrates exhibit the most pronounced response. As a result of this wettability shift, displacement efficiency for residual oil films in quartz cores can reach up to 93 percent, indicating strong recovery performance.
Studies on zwitterionic surfactants, including TR-880, NX-2760, and NX-1510, have examined their mechanisms in carbonate reservoirs. These surfactants operate through a dual-action mechanism. They contribute to both a marked reduction in oil-water interfacial tension and a favorable shift in rock surface wettability. By promoting a more water-wet state on the core surface, these agents help overcome capillary resistance, supporting improved oil recovery in tertiary processes.