Phase Diagram Optimization in Micellar Systems

Abstract

Abstract An optimization of micro emulsion compositions is presented for a hydrocarbon/water ratio considered as characteristic. By studying the influence of the main parameters (molecular weight of hydrocarbon and amphiphilic compounds, surfactant to co surfactant concentration ratio, salinity and temperature), the results obtained show an optimal value for each of them, corresponding to the use of a minimal amount of amphiphilic compounds. An interpretation is given, based on the equilibrium of hydrophilic and hydrophobic tendencies within the surfactant molecule, and supported by interfacial tension measurements in simpler diphasic systems where the partitioning of the surfactant between aqueous and hydrocarbon phases can be determined. Thus a set of relationships between the parameters is established that may prove useful, from a practical point of view, in the choice of formulations. In particular, solutions are given for high temperature and brine concentration. INTRODUCTION Micellar solutions used in enhanced oil recovery present certain difficulties, as regards both their preparation and their application. These difficulties are further increased by economic requirements as the limits imposed by technical possibilities and profitability narrow the field of possible compositions. In the application of this process, guides are therefore required to reach optimal formulations, i. e., in particular, the use of a minimal amount of amphiphilic compounds. The search for maximal interfacial efficiency of surfactant entails establishing conditions in which there is a maximal concentration at the interfaces. This should take place when the amphiphilic molecule shows minimal affinity in the aqueous phase and hydrocarbon phase simultaneously; the hydrophilic and hydrophobic tendencies are then very close and balance each other. A similar phenomenon appears when a minimal interfacial tension is obtained in the systems composed of a hydrocarbon and a surfactant diluted aqueous solution. The advantage of these systems is that the partitioning of the amphiphilic product is easily measured and the affinity equilibrium thus is well shown.