Foam-oil interactions analyzed by static foam tests

There have been many foam field applications in the North Sea area in the recent years. One of the key questions of foam stability is the tolerance to presence of oil in the reservoir. In order to understand the influence of oil saturation on foam, more fundamental experimental studies have been performed. The static foam properties have been investigated by variation in surfactant concentration, amount of added oil, and variation in polarity of the oil phase. An alpha-olefin sulfonate surfactant is used in all experiments. The foam generation ability is connected with surfactant concentration. Foam is also formed with the AOS surfactant even below the critical micelle concentration. For the ionic strength area investigated, foam height for AOS solutions does not change, but foam tests with decane and crude oil are stabilized with lower ionic strength. The foam stability in the presence of alkane-type oils is related to the molecular weight of the oil molecule. The foam generation and stability is possibly connected to the surfactant ability to solubilize oil molecules. Alkanes that solubilize in the micelles seem to destabilize the foam. In crude oil systems more complex relations seem to be active. Alkanes with molecular weight higher than decane are too large to be solubilized in the micelles. The molecules will therefore have less ability to be transported out of the foam and oil seems to stabilize the foam. We have used a multivariate analysis to identify the most important factors influencing foam stability in the presence of oil.