Improved oil recovery by adsorption-desorption in chemical flooding

Surfactant loss is one of the major concerns with chemical oil recovery processes in which surfactant is one of the components of the chemical formula. Surfactant loss due to adsorption on the reservoir rocks weakens the effectiveness of the injected chemical slug in reducing oil-water interfacial tension (IFT) and makes the process uneconomical. Adsorption-related interfacial tension behavior and its effect on oil recovery has not been understood completely. This paper reports the investigation of oil-water IFT behavior when the chromatographic separation of the surfactant mixture occurs during surfactant/alkaline corefloods. In this work, surfactant and alkaline concentrations in the effluent of corefloods and oil-water interfacial tension were determined under different injection strategies. It was found that, in an extended waterflood following an alkaline-surfactant slug injection, surfactant desorbed into the water phase. This desorption of surfactant lasted for a long period of the waterflood. Although the concentration of the desorbed surfactant in the extended waterflood was very low, an ultra-low oil-water IFT was obtained by using a suitable alkaline concentration. Coreflood results showed that an additional 13% of the initial oil in place (IOIP) was recovered after the alkaline-surfactant injection by the synergism of the desorbed surfactant and alkaline. This result indicates that the efficiency and economics of a chemical flood could be improved by utilizing the desorbed surfactant during extended waterflood processes. (C) 2004 Published by Elsevier B.V.