Case studies for the feasibility of sweep improvement in surfactant-assisted waterflooding

Volumetric sweep inefficiencies can arise in waterflooding because of reservoir heterogeneity: the present work addresses, by computer-simulated case studies, the technical feasibility of a novel sweep improvement process which utilizes the chromatographic and phase behavior of dissimilar surfactants and their mixtures to plug high-permeability “thief zones”. Case studies are presented for waterfloods without and with the process. They reveal that low-permeability plugs can be grown from any starting point and will selectively penetrate the high-permeability zones for large permeability contrasts, where sweep inefficiency is high. Selectivity decreases when the contrast is small or the injection interval long. For strong permeability reduction, the optimum plug is located between one-half and three-quarters of the way along the high-permeability zone; larger plugs are unnecessary. Oil recoveries using the process approach those possible with ideal plug placement.