Effect of surfactant structure on foam–oil interactions: Comparing fluorinated surfactant and alpha olefin sulfonate in static foam tests

There have been many foam field applications in the North Sea in recent years. A key question is the stability of foam in the presence of oil in the reservoir. To understand the influence of oil type and of oil saturation on foam stability and foam generation various fundamental experimental studies have been preformed.In this study results from static foam experiments with a fluorinated surfactant are compared with tests done with an alpha olefin sulfonate [A.K. Vikingstad, A. Skauge, H. Hoiland, M.G. Aarra, Colloids Surf. A: Physiochem. Eng. Aspects 260 (2005) 189–198.]. The static foam properties for the two surfactants have been investigated by variation in surfactant concentration, in amount of added oil, and in polarity of the oil phase.The effectiveness of foam generation is related to surfactant concentration. The fluorinated surfactant gave more stable foam over time at the same surfactant concentration. Foam formed below the critical micelle concentration for both surfactants. Without oil present, both surfactants have foam heights that are independent of ionic strength.In our opinion, foam stability in the presence of alkane-type oils is related to the molecular weight of the oil molecule. Foam generation and stability is possibly connected to the surfactant's ability to solubilize oil molecules. Foam tests with decane or crude oil stabilized at lower ionic strength for the AOS surfactant. The foam height for the fluorinated surfactant showed little sensitivity to oil.For the AOS surfactant alkanes that were soluble in the micelles seemed to destabilize the foam. Experiments done with the fluorinated surfactant did not show this behavior. In fact, much more foam was generated in tests with alkanes that solubilize in the micelles than for those that were not.