Synergy of Polymer Mobility Control and Surfactant for Interface Elasticity Increase in Improved Oil Recovery

Summary The injection of modified brines is one of the most studied improved oil recovery (IOR) methods for sandstone and, more recently, carbonate reservoirs. Examples include low-salinity waterflooding, surfactant injection for residual oil reduction, and polymer injection to improve sweep efficiency. Polymer addition to injection water has had many field successes. Polymer and surfactant injections are often effective, but 2,000–10,000 ppm concentrations may make the processes expensive. We have recently suggested the idea of an ultralow concentration of polymeric surfactants (PSs) at 100 ppm to decrease residual oil saturation (ROS) from increased brine-oil interface elasticity. This work investigates the synergistic effect of polymers for sweep efficiency and the increase in interfacial elasticity with PSs. The combined formulation may provide both sweep efficiency and residual oil reduction. The effect of polymer on ROS is also examined in our investigation. Coreflooding tests are performed on carbonate rocks using four crude oils and a variety of aqueous injection fluids—two high-salinity brines combined with a nonionic PS and two different polymers. Polymers are found to improve recovery at breakthrough via the increase in injection brine viscosification. They may reduce or increase ROS. The PS promotes higher final recovery by increasing the interfacial oil-brine elasticity. When using both a PS and a polymer, breakthrough is delayed, and final recovery is improved compared with polymer alone. Oil recovery may be a strong function of oil-brine interfacial viscoelasticity in polymer flooding.