Foam stability in the presence of oil: Effect of surfactant concentration and oil type

One of the main concerns in the application of foam for enhanced oil recovery is the influence of oil on foam stability. This paper reports a systematic laboratory study of foamability and foam stability in the absence and in the presence of alkane-type oils for various surfactants. Foam was generated by sparging nitrogen gas at a fixed flow rate through the surfactant solution. We first examined the foaming properties of selected commercial surfactants used in the petroleum industry (Dowfax 8390, C12-15 Enordet, Petrostep SB, and C14-16 AOS). It was found that C14-16 AOS exhibited the best foam stability in the presence of oil. Then we characterized the foaming behavior of AOS by varying surfactant concentration and oil types. We measured precisely the evolution of the foam volume and the amount of liquid volume in the foam. AOS surfactant exhibited a good foamability in the presence of alkanes with different carbon chains. The generated foam decayed in three main stages: first a small and rapid decay in foam volume occurred at early times, followed by a stabilized foam volume extended for a certain period, and then a second decay by which foam volume decreased continuously over a relatively long time to reach its final volume.From the liquid volume in the foam it was found that the first decay was dominated by gravity drainage, while bubble coalescence played a main role during the second decay. The presence of oil led to AOS foam entering the second decay at an earlier time. The oil destabilizing effect was more pronounced for alkanes with a shorter carbon chain. Foam stability and liquid volume in the foam increased with surfactant concentration. The obtained results for foam stability in the presence of oil were discussed in terms of the classical entering/spreading coefficient, oil solubilization effect and stability of pseudoemulsion film. (C) 2013 Elsevier B.V. All rights reserved.