Several decades of research have led to general acceptance that a negative salinity gradient represents the optimal injection strategy in surfactant-polymer (SP) and alkaline-surfactant-polymer (ASP) flooding. However, in many situations, such as when formation brine salinity is low either naturally or due to extensive waterflooding, a classical, negative salinity gradient is not feasible. In this case, other options may include the retention of a negative gradient between the slug and drive, but with the allowance of type I formation brine salinity, or a "I-III-I" gradient. We investigate how this strategy will affect flood performance in respect to a classical, negative, or "II-III-I" gradient. Corefloods and 1-D simulations are used to compare the production profiles of the two, and additional simulations examine the difficulty in capturing the tradeoff between low interfacial tension and phase trapping near the transition between type I and type III phase behavior.

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