On the Phase Behavior of Systems of the Type H₂O — Oil — Nonionic Surfactant — Electrolyte

Abstract

In a recent publication we had suggested study of “simple” systems of the type H₂O — Oil — Nonionic Surfactant — Electrolyte as model for the pseudoquaternary systems relevant in tertiary oil recovery, in order to make qualitative predictions for the phase behavior of such systems. In this paper the first results of such studies are presented. It is shown in detail how the formation of the three-phase triangle arises from the change of the phase diagram of such systems with temperature. It turns out that, within a limited temperature range, the phase diagrams can show two critical points, which are responsible for the ultra-low interfacial tensions between neighbouring phases of the three-phase triangle. Furthermore, a simple recipe is proposed which permits to predict whether or not a system — with given oil — will show a three-phase triangle with rising temperature or addition of an appropriate electrolyte. The predictions are compared with experiments using short chain polyglycolethers (C_iE_j) as surfactants, which have the advantage that these surfactants do not form anisotropic phases.