The steady flow and viscoelastic properties of kerosene-inwater and mineral oil-in-water emulsions were investigated. using a controlled-stress rheometer. The rheological parameters (viscosity, storage modulus and loss modulus) show a substantial increase upon reduction of the droplet size of the emulsions. When fine and coarse emulsions having the same volume fraction of droplets (and the same oil) are mixed together in varying proportions, the resulting mixed emulsion exhibits a minimum in the viscosity, storage and loss moduli plots at a certain proportion of the fine droplets. However, the minimum in viscosity occurs only at low shear stresses. At high stresses. the viscosity of the mixed emulsion increases linearly with the increase in the fine emulsion content on a semi-log scale.
An "emulsion" is a two-phase oil/water system where one of the phases is dispersed as droplets in the other. Emulsions also contain a third component. called the emulsifying agent or emulsifier. which has two principal functions:
to decrease the interfacial tension between oil and water thereby enabling easier formation of the emulsion;
to stabilize the droplets against coalescence once they are formed.
Emulsions are encountered at nearly every step of the petroleum production and recovery operations viz. within the underground porous media (oil reservoir) at wellheads in phase separators in flotation units in crude oil transport facilities and at various stages of the refining process.
Recently, considerable interest has been shown in the use of emulsions for pipeline transportation of highly viscous crude oilsl. The transportation of extremely viscous crude oils. such as bitumen and heavy oils. by pipelines is difficult, especially during cold weather. To facilitate the flow of very viscous crude in pipelines. it is necessary to either heat the oil to reduce its viscosity or dilute the oil with a low viscosity hydrocarbon diluent. In the former case. heating cost and pipeline insulation costs are generally very high. In the latter case. the cost of diluent and its availability pose difficult problems. However. these problems can be avoided if the crude oil is transported in the form of an oil-in-water (O/W) emulsion. For emulsion pipelining to be economical. it is important to keep the oil concentration of the emulsion as high as possible. and at the same time. maintain the, emulsion viscosity at a reasonable level. It is believed thii(the key factors that determine the emulsion viscosity at high oil concentrations are the droplet size and the droplet size distribution. However. little research work has been carried out on the influence of droplet size and droplet size distribution upon emulsion rheology.
In the past. numerous theoretical and numerical studies have been conducted on the motion/deformation of emulsion droplets and emulsion rheolog2–41. In the low-Reynolds number limit. emulsion rheology depends upon the following factors: volume fraction of the dispersed phase (Ø). ratio of the dispersed-to-continuous-phase viscosities (K) and the capillary number (NC1) The deformation of the droplets in shear flow causes normal stresses and shear-thinning behaviour in emulsions.
