Viscosity effects occurring in aqueous solutions containing a combination of surfactants, polymers and salts are of considerable interest in enhanced oil recovery operations. High molecular weight polymers, which are normally employed to improve sweep efficiency, lose much of their viscosity because of mechanical degradation and other adverse conditions in the reservoir. The mixing of the surfactant slug with the polymer slug in micellar flooding may lead to phase instability and low recovery efficiency. The formation of surfactant-polymer aggregates on the other hand, might have a positive effect on recovery. Such association complexes do not lose their viscosity permanently due to shear as they are quickly rebuilt upon cessation of shear forces. The present work shows that significant viscosity increases can be obtained by combining a petroleum sulfonate surfactant with a low molecular weight polyethylene oxide. For example, an addition of Carbowax®−20M to 4% Petrostep®−420 at 1.5% NaCl salinity first results in a viscosity increase with a maximum at about 0.2% of polymer. After this, the viscosity drops sharply reaching a minimum at 0.5% of polymer. Beyond this point, the viscosity begins to rise again at a rate which is somewhat higher than that observed for the polymer solution alone. The behavior observed with Carbowax®−6000 was similar although the increase in viscosity was smaller. No discernible effects were observed with Carbowax®−600. The magnitude of the viscosity increase observed at 0.2% of polymer was found to be strongly dependent on salinity.
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