(462e) Alkaline/Surfactant Process for Enhanced Oil Recovery

Alkaline/surfactant processes for enhanced oil recovery produce ultralow interfacial tensions by using a combination of an injected surfactant and soaps formed under alkaline conditions from naturally occurring naphthenic acids in the crude oil. Because interfacial tension depends on the local ratio of soap to surfactant, it is essential to understand transport of each of the two surfactants through the reservoir. A one-dimensional, two-phase finite difference simulator has been developed, which tracks soap, surfactant, alkali and polymer concentrations as a function of position and time as well as oil and aqueous phase saturations. It includes adsorption of surfactant and polymer and longitudinal dispersion. Its predictions show that a gradient in soap-to-surfactant ratio develops during the process and propagates through the reservoir. As ultralow tension is achieved at the appropriate ratio, this behavior assures a robust process. Recovery is dependent on the range of concentrations over which tension is low around optimal conditions and on maintaining adequate mobility control, i.e., having sufficiently high viscosity in the ASP slug and polymer drive. Predictions of oil recovery by the simulator are in good agreement with experimental results from sand pack ASP floods for both dolomite and silica sands.