On Determining the Continuous Phase in Microemulsions

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Abstract
In light of recent advances in the use of micellar solutions (microemulsions) in oil recovery and well stimulation, it has become important to define accurately the physical properties of these systems. One aspect of such work is to distinguish between the disperse phase and the continuous phase, particularly at extreme concentrations of either water or hydrocarbon. Conventional techniques for making this distinction include the dye solubility method, the phase dilution method, the conductivity method, and the fluorescence method. However, a single test may give ambiguous results. We shall present here viscosity, conductivity, and miscibility data for a series of micellar solutions that are comparable in composition with those applied in the field. Example 1 shows data obtained with a micellar solution prepared with a 420 equivalent weight (eq. wt.) petroleum sulfonate (of our own manufacture) to which was added 1-pentanol to produce a single-phase, optically clear system. Both conductivity and miscibility data indicate phase inversion between 2.2 and 2.3 volume percent 1-pentanol. Further, the data show that the inversion was from oil-external to water-external as the amount of 1-pentanol in the system increased. Continued addition of this cosurfactant (2.6 volume percent) led to separation of an aqueous phase. percent) led to separation of an aqueous phase. This observation is similar to those made by Winsor and Bowcott and Schulman, in that a system with the characteristics of a water-external micellar solution can exist in equilibrium with excess aqueous phase. Most of the brine had been expelled from the micellar solution, at 3 volume percent 1-pentanol. At this point, the conductivity decreased markedly; and the point, the conductivity decreased markedly; and the remaining micellar solution became miscible with hydrocarbon. Example 2 shows data obtained with the same petroleum sulfonate and cosurfactant. However, in petroleum sulfonate and cosurfactant. However, in this case the micellar solution contained 70 weight percent brine as opposed to 30 weight percent of percent brine as opposed to 30 weight percent of Example 1. No evidence of phase inversion is present over the single-phase region, and both conductivity and miscibility data indicate a water-external system. Example 3 shows the results obtained with a micellar solution prepared with a 470 equivalent weight petroleum sulfonate (commercially available).

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