SPE 169726 Microemulsion Flow in Porous Media: Potential Impact on Productivity Loss Mehdi Izadi, TIORCO LLC., Hossein Kazemi, Colorado School of Mines., Eduardo J Manrique., Mahdi Kazempour., Neeraj Rohilla, TIORCO LLC Copyright 2014, Society of Petroleum Engineers This paper was prepared for presentation at the SPE EOR Conference at Oil and Gas West Asia held in Muscat, Oman, 31 March–2 April 2014. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract 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. Introduction Chemical EOR techniques improve oil recovery both in secondary or tertiary floods in variety of reservoir conditions (Demin et al., 1997; Hernandez et al., 2002; Pandey et al., 2008; Shutang et al., 1996; Vargo et al., 2000; Wyatt et al., 1995). Despite their worldwide applications and encouraging results, productivity loss has been observed in some fields (Sharma et al, 2013., Hashmi et al., 2013, Christopher et al, 1988). Productivity loss not only is associated with SP/ASP flooding, it is also associated with polymer flood (Hashmi et al., 2013). New studies on porous media microemulsion flow and rheology have been reported (Humphry et al., 2013; Walker et al., 2012). Productivity loss during ASP/SP/P flooding can be attributed to the following causes:  High polymer concentration  Mineral precipitation common in ASP injection -- causing pore plugging/permeability impairment due to scale formation or stabilizing in-situ emulsions (Pickering effect)  Polymer-microemulsion-mineral interaction -- causing large viscosity of in-situ microemulsion  Surfactant loss causing change in displacement mechanism -- Type III to type II phase transformation In ASP/SP flooding, surfactant lowers interfacial tension (IFT) between displacing aqueous phase and trapped oleic phase (Liu, Miller, Li, & Hirasaki, 2010; Liu et al., 2008). In early days of surfactant flooding, a low-concentration surfactant brine (low-tension flooding), followed by polymer solution, was injected to mobilize residual oil and improve sweep efficiency. It was common to flush the reservoir with low-