Influence of salinity and hardness on the micellization of an extended surfactant studied by turbidimetry

Abstract

The injection of surfactants as the active component of Enhanced Oil Recovery (EOR) formulations is the current chemical method with the more promising potential because it produces substantial reduction of oil/water interfacial tension. However, the molecular arrangements depending on salinity and hardness, is not well understood. This is a key factor when trying to understand the solubilization of oil and the retention of surfactant during EOR processes. Nevertheless, the formation of micelles is one of the phenomena most affected by the salt concentration but, usually, this parameter is not considered. In this work, the micellization of a commercial extended surfactant at different concentrations and several salinities and hardness is studied. Results showed that size, shape and/or number of micelles are affected by the salinity and hardness. The explanations for this fact include the formation and re-solubilization of calcium soaps, salting-out phenomena and the electric charge shielding, which affect the micellar packing factor. The re-arrangement of molecules, depending on the electrolytes in solution, could favor the formation of spherical, rod-like micelles, and eventually the co-existence of both, or even other types of aggregates and it could be inferred by the analysis of set of data obtained from simple and cheap technique as turbidimetry and complimentary verified by a more sophisticated technique such like DLS.