Resolving an Enhanced Oil Recovery Challenge: Optimum Formulation of a Surfactant-Oil-Water System Made Insensitive to Dilution

Upon dilution by the petroleum reservoir connate water, the anionic commercial surfactant blend often used in enhanced oil recovery by low tension, becomes more lipophilic at the interface because of so-called selective partitioning. Hence, the optimum formulation is not maintained when the injected slug moves through the reservoir. An opposite variation is found for ethoxylated nonionic surfactant systems. As a consequence of these antagonistic influences, the optimum formulation shift produced by dilution may be eliminated by using an appropriate mixture of anionic and nonionic commercial surfactants, so that the two effects exactly cancel out.