Multiphase Microemulsion Systems

Economical microemulsion flooding inevitably involves microemulsion phases immiscible with oil, water or both; and oil recovery is largely affected by displacement efficiency during the immiscible regime. Therefore, it is pertinent to study interfacial tension in relation to multiphase microemulsion behavior. Three basic types of multiphase systems are identified and used to label phase transitions that occur when changes are made in salinity, temperature, oil composition, surfactant structure, cosolvent, and dissolved solids in the aqueous phase. Directional effects of these changes on phase behavior, interfacial tension, and solubility number are tabulated for the alkyl aryl sulfonates studied, and conjectured to hold for all anionic surfactant systems. This approach provides a convenient method for preliminary screening of surfactants for tertiary oil recovery. Interfacial tensions were found to correlate with solubility number in the various microemulsion phases. (18 refs.)