A comprehensive investigation of emulsion viscosity in oil-water mixtures is presented in this work. A novel rheometer design was used to measure the viscosity of various crude oils with differing compositions (1 < μ < 2400 cP, 0.7 < rSG < 0.9) and water chemistries (5.16 < pH < 8.4.) The impact of rheometer design on flow pattern and shear experienced by fluid was evaluated using computational fluid dynamics (CFD). The results of the CFD were further benchmarked experimentally using a well-defined non-Newtonian fluid. The results of approximately 1,000 emulsion viscosity data points were compared to 5 models available in the literature. Yaron and Gal-Or (1972) was found to predict the data best without any modifications. The Pal and Rhodes (1989) model was fit to the data which allowed for a detailed investigation of the effects of shear rate, water chemistry and chemical interactions. The emulsions demonstrated a shear thinning tendency which would be best approximated using a power law fluid model. It was observed that for two of the crude oils investigated, an increase in water pH resulted in an increase in emulsion viscosity. The results of chemical interactions demonstrated the importance of fluid specific testing and applications to oil field predictions was highlighted. This investigation reinforces the need for more advanced standards with respect to evaluating oil field chemicals, namely demulsifier, on emulsion hydraulics.
The production of oil and gas from a reservoir is almost always accompanied by a water phase. The commingling of the water and oil phases can result in one phase being dispersed in the other, and if the appropriate surface active components are present, the dispersed phase can form a very stable emulsion. Emulsion stability, its impact on pipeline hydraulics, and the challenges associated with the separation of oil and water are well documented throughout the industry. There exist several comprehensive resources with respect to emulsions in the oil industry (Sjoblom, 2001; Schramm, 1992). A more recent review by Kokal (2005) highlighted the current state-of-the-art knowledge with respect to the industries understanding on emulsions. These resources provide very detailed background which will not be replicated here.
As noted in previous work, the effective viscosity of an emulsion can be significantly higher than the bulk, or continuous phase. While this is generally agreed throughout the literature, there have been several methodologies used to measure the effective viscosity.