Surfactant-polymer (SP) flooding is an enhanced oil recovery (EOR) technique used to mobilize residual oil by lowering the oil-water interfacial tension, micellar solubilization, and lowering the displacing phase mobility to improve sweep efficiency. Surfactant-polymer flooding, also known as micellar flooding, has been studied both in the laboratory and field pilot tests for several decades. Traditionally, a tapered polymer solution follows the injected surfactant. However, in recent years co-injection of surfactant and relatively high concentration polymer solution has been used in several field trials. Despite significant increase in oil recovery in the early stage of surfactant-polymer flooding, in some projects, the early increase in oil productivity period has been short followed by significant reduction in well productivity. We believe productivity loss results from surfactant-polymer interaction and fluid rheology alterations near production well. To evaluate this hypothesis, we injected microemulsion (with and without polymer) in Berea core plugs at residual oil saturation, and chased the surfactant with polymer solution or water. The objective was to determine the cause of productivity reduction and to develop a numerical model for simulating SP flooding in the field.

To achieve our objective, we searched for causes of productivity loss in field when using SP flooding. The search indicated that polymer-microemulsion interactions lead to high-pressure drop and significant productivity loss at the production well. Numerical modeling of several core floods pointed to the same conclusions because the numerical model required a large residual resistance factor (RRF) or a highly viscous aqueous phase near the production end. This information will be used to improve the design of future ASP/SP fluid systems.

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