Advantages of an APS/AES Seawater-Based Surfactant Polymer Formulation

Abstract

SummaryA low-complexity chemical flooding formulation has been developed for application in offshore environments. The formulation uses seawater with no additional water treatment beyond that which is normally performed for waterflooding (filtration, deoxygenation, etc.). The formulation is a mixture of an alkyl propoxy sulfate (APS) and an alkyl ethoxy sulfate (AES) with no cosolvent. With seawater only (no salinity gradient), the blend of APS and AES gives substantially higher oil recovery than a blend of APS and internal olefin sulfonate (IOS) in outcrop sandstone. This formulation also reduces complexity, increases robustness, and potentially improves project economics for onshore projects as well.It is shown that the highest oil recovery is obtained with surfactant blends that produce formulations that are underoptimum (Winsor Type I phase behavior) with reservoir crude oil. Also, these underoptimum formulations avoid the high-injection pressures that are seen with optimum formulations in low-permeability outcrop rock. The formulation recovers a similar amount of oil in reservoir rock in the swept zone. Overall recovery in reservoir rock is lower than outcrop sandstone due to greater heterogeneity, which causes bypassing of crude oil.A successful formulation was developed by first screening surfactants for phase behavior then fine tuning the formulation based on insights developed with corefloods in consistent outcrop rocks. The consistency of the outcrop is essential to understand cause and effect. Then, final floods were performed in reservoir rock to confirm that low interfacial tension (IFT) is propagated through the core.