Enhancing Foam Stability by the Use of Surfactants Mixtures for EOR Purposes

This experimental research investigates the opportunity to enhance the oil recovery by enhancing the foam stability by the use of surfactants mixtures in comparison with individual surfactants. The mixtures were prepared with commercially available individual surfactants. They were also tested and compared with the individual surfactants in terms of foam stability in presence and absence of crude oil, mobility reduction, and enhancing the oil recovery. The screening and comparison processes were achieved in four experimental stages: preliminary experimental work, static tests combined with both interfacial tension measurements and bubbles sizes, dynamic tests for mobility control evaluation and core flooding experiments for oil recovery. Shaking tests showed that binary surfactants mixtures perform better when a good foamability agent was mixed with a good foam-oil stabilizer. Observations indicated that mixtures are better in foam stability in presence and absence of crude oil, lower in CMC, lower in σg/w and σo/w, generated higher foam viscosity in porous media and produced more oil than individual surfactants. In comparison with AAS anionic surfactant, mobility results showed a 5.12-fold decrease in mobility using AAS-IOS mixture, 6.32-folds using AAS-AAS mixtures, and 3.42-folds using AAS-nonionic mixture. Moreover, AAS produced 2.5% additional oil recovery compared with 7.5% with AAS-IOS, and 7.48% with AAS-AAS mixture. Mobility control evaluation in the high permeability, in-house built, glass beads pack resulted in higher foam viscosity when using individual surfactants. However, the mixtures proved better performance in low permeability porous media at low shear rate. The contradictory behaviors were related to the differences in micellar stabilities of the individual surfactants and their mixtures. For mobility control of ScCO₂, two anionic surfactants were examined and compared in terms of mobility reduction and in-situ foam viscosity. The newly developed complex nanofluid (CNF) surfactant generated higher foam viscosities at all conditions with and without salinity than that of AOS surfactant. In comparison with 27.54% additional oil recovery of ScCO₂ injection, AOS/ScCO₂ co-injection produced 1% more oil recovery, and CNF/ScCO₂ co-injection produced 8% addition oil recovery