Rheological and Electrical Test Methods for Evaluation of Structure Development in Oil and Water Mixtures 951031

Intentionally adding water to oil, in the laboratory, provides an indication of the oil's ability to tolerate the presence of water. Various characteristics, such as emulsion, haze or separation, may be observed. Some blends of oil and water have been shown to form structures when left undisturbed. A visual, qualitative, storage test is capable of detecting this phenomenon as the presence or absence of structure. However, the time frame of formation can be on the order of days or weeks and is sensitive to handling and temperature effects. Quantitative methods are required for any evaluation of chemistry, temperature and handling effects on the rate and strength of structure formation. This paper describes rheological and electrical methods which directly and indirectly measure the tendency to form a structure at the molecular level, yielding rate of formation and strength information.

The rheology method measures the elastic and viscous moduli of the system through an oscillatory stress/strain procedure, a direct measurement of the physical interaction of particles/structures. While the strength of a final structure can approach 150 Pascals (elastic modulus), this method can detect changes in the elastic modulus below 1 Pascal. The rate of increasing interactions between particles/structures can be determined. This method can also detect an inversion phenomenon which occurs at elevated temperatures.

Methods which measure electrical characteristics were also used to evaluate these structured systems. These measurements imply the formation of structures which incorporate water. These measurements are consistent with the rheology measurements; samples with higher elastic moduli have greater conductivity and more highly charged particles. Systems with increased conductivity and charging will have more extensive structures which cause higher elastic moduli.