Trends to Attain a Lower Interfacial Tension in a Revisited Pure Alkyl Polyethyleneglycol Surfactant–Alkane–Water Ternary System. Basic Concepts and Straightforward Guidelines for Improving Performance in Enhanced Oil Recovery Formulations

Abstract

AbstractSurfactant–oil–water systems exhibit a low interfacial tension minimum when the interactions between the adsorbed surfactant with water exactly coincide with its interactions with oil. This occurrence takes place at the so‐called optimum formulation, which was conceptually derived by Winsor in the 1950s and rendered by numerical correlations for enhanced oil recovery in the 1970s. The actual low value of the interfacial tension minimum has been found to increase or decrease with formulation variables and though some hints are available, no general relationship has been reported up to now, probably because too many variables are involved in complex interactions. It is shown in the present article that a linear relationship between low‐tension performance and formulation variables can be found for very simple ternary systems containing a pure ethoxylated alcohol, n‐alkane and water at variable temperature, i.e., when there are only four degrees of freedom. In such a case the iso‐performance contours studied in bi‐dimensional spaces are reported to be almost straight lines and as a consequence the path to lower the tension through formulation adjustments is easy to find as being perpendicular as possible to the contours. On the other hand, it is shown that displacing the limit of restrictions like the surfactant precipitation boundary is a priority issue, thus justifying many trends which have been proposed on empirical grounds in the past years. The reported simple guidelines for a simple surfactant–oil–water ternary is likely to considerably facilitate the formulator's work in a real system with a score of formulation variables.