What Causes the Formation of Water-in-Oil Emulsions?

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Abstract
The results of studies conducted over the past 6 years to characterize why water-in-oil emulsions form are summarized. It is shown that water droplets are held in oil by a combination of viscous and interfacial forces. The stability of an emulsion is very important in understanding its formation because stability is the endpoint or measurement of the entire process. Emulsions can be grouped into three categories: stable, unstable, and mesostable. Each has distinct physical properties. For example, the viscosity of a stable emulsion at a shear rate of I reciprocal second is at least three orders-of-magnitude greater than that of the starting oil. An unstable emulsion usually has a viscosity no more than two orders-of-magnitude greater than that of the starting oil. The zero-shear-rate viscosity is at least six orders-of-magnitude greater than the starting oil for a stable emulsion. For an unstable emulsion, it is usually less than two or three orders-of-magnitude greater than the viscosity of the starting oil. and finally, a stable emulsion has a significant elasticity, whereas an unstable emulsion does not. The stability of emulsions has been studied by examining their asphaltene content and their resin content. Results are reported showing that asphaltenes and resins are responsible for stability. It is noted that, given the correct chemical composition, primarily asphaltenes, sea energy is needed. The properties of the starting oil are the important factor in determining what type of water-in-oil state is produced. Composition and property ranges are given for the starting oil to form each of the water-in-oil states. Important property factors are the asphaltene content, resin content, and starting oil viscosity.

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