Mechanistic Modeling of Alkaline/Surfactant/Polymer Floods

Abstract

Summary Alkaline/surfactant/polymer (ASP) flooding is of increasing interest and importance because of high oil prices and the need to increase oil production. The benefits of combining alkali with surfactant are well established. The alkali has very important benefits such as lowering interfacial tension (IFT) and reducing adsorption of anionic surfactants that decrease costs and make ASP a very attractive enhanced-oil-recovery method, provided that the consumption is not too large and the alkali can be propagated at the same rate as the synthetic surfactant and polymer. However, the process is complex, so it is important that new candidates for ASP be selected taking into account the numerous chemical reactions that occur in the reservoir. The reaction of acid and alkali to generate soap and its subsequent effect on phase behavior is the most crucial for crude oils containing naphthenic acids. Mechanistic simulation of the ASP flood considering the chemical reactions, alkali consumption, and soap generation and the effect on the phase behavior is the key to success of future field operations. Using numerical models, the process can be designed and optimized to ensure the proper propagation of alkali and effective soap and surfactant concentrations to promote low IFT and a favorable salinity gradient. In this paper, we describe the ASP module of the UTCHEM simulator, which is the University of Texas chemical compositional simulator, with particular attention to phase behavior and the effect of soap on optimum salinity and solubilization ratio. Phase behavior data are presented for sodium carbonate and a blend of surfactants with an acidic crude oil that followed the conventional Winsor phase transition with significant three-phase regions even at low surfactant concentrations. The solubilization data at different oil concentrations were successfully modeled using Hand’s rule. Optimum salinity and solubilization ratio were correlated with soap mole fractions using mixing rules. ASP coreflood results were successfully modeled taking into account the aqueous reactions, alkali/rock interactions, and phase behavior of soap and surfactant. Mechanistic simulations give insights into the propagation of alkali, soap, and surfactant in the core and aid in future coreflood and field-scale ASP designs.