Surfactant Transport upon Foam Films Moving through Porous Media

In the context of foam improved oil recovery or foam-based soil/aquifer remediation, a model is presented for evolution of surfactant surface concentration on foam films moving through porous media. The model exploits an analogy between surface transport behaviour in foam fractionation and surfactant transport behaviour for foam in porous media. Films either stretch as they move from pore throat to pore body, or shrink when moving from pore body to pore throat: this stretching/shrinking then influences surfactant concentration. In addition, Plateau borders at the edges of films can supply surfactant to films, or receive surfactant from them. The model is solved numerically and key parameters governing its behaviour are identified. Parameter regimes are encountered, corresponding to modest stretching or shrinkage rates, in which surfactant concentration on films is predicted to be closely coupled to surfactant concentration in Plateau borders. Alternate parameter regimes are encountered, corresponding instead to fast stretching or shrinkage rates, in which surfactant concentration on films is predicted to become independent of surfactant concentration in Plateau borders. Asymptotic solutions available in each of these regimes are compared with numerical solutions. A preliminary comparison between the model predictions and experimental data from literature is also described. The appeal of the model is that predictions can be made comparatively simply. Indeed the model can predict when foam films might become significantly depleted in surfactant, possibly leaving films liable to breakage, which would then be detrimental to foam in porous media applications.