Studies of Water-In-Oil Emulsions: Stability Studies

摘要

Studies to determine the stability of water-in-oil emulsions were conducted. Three oils were used to form emulsions and these were studied by rheological methods. It has been noted thai the stability of emulsions can be grouped into three categories: stable, mesostable and unstable. The differences in the emulsion types are readily distinguished both by their rheological properties, and simply by appearance. The apparent viscosity of a stable emulsion at a shear rate of one reciprocal second, is at least three orders-of-magnitude greater than the fresh oil. An unstable emulsion usually has a viscosity no more than one order-of-magnitude greater than that ofthe starting oil. A stable emulsion has a significant elasticity, whereas an unstable emulsion does not. It should be noted that very few emulsions have questionable stability. Stable emulsions have sufficient asphaltenes (>approx.5%) to establish films of these compounds around water droplets. Mesostable emulsions have insufficient asphaltenes to render them completely stable. Stability is achieved by viscoelastic retention ofwater and secondarily by the presence of asphaltene or resin films. Mesostable emulions display apparent viscosities of about 80 to 600 times that ofthe starting oil and true viscosities of 20 to 200 times that ofthe starting oil. A comparison of viscometer readings for characterizing emulsions was made.