Oil/Water Emulsions for Pipeline Transport of Viscous Crude Oils

Abstract

ABSTRACT Heavy (viscous) crude oils have become an increasingly important source of hydrocarbons in many parts of the world. Transport of these viscous crudes from the source to the refinery can be a problem. In a number of producing areas, a pipeline is in place, but the line was designed for lighter (less viscous) crudes. Pipeline transport can be effected by heating, dilution with lighter fractions, or thermal viscosity breaking. All of these techniques are expensive and are not practical in many situations. Techniques are needed to reduce the pumping costs without significantly increasing the handling costs at: either end of the pipeline. High oil content oil-in-water emulsions have been shown to be a viable alternative to the techniques mentioned above. Dramatic decreases in viscosity can be achieved while transporting a fluid which has an oil content of 70% or greater. A knowledge of the rheological behavior of these emulsions, under both laboratory and field conditions, is important. In this study, four different viscous crude oils were used. The viscosities ranged between 2000 and 500,000 (estimated) centipoise (2.0 to 500 Pa·s). The emulsions ranged from 60 to 72.5% oil in tap water stabilized with an emulsion stabilizer. Rheological measurements were carried out with a tube flow viscometer equipped with three tube sizes and a concentric cylinder viscometer (Rheometrics Pressure Rheometer). The data obtained showed that the shear stress-shear rate behavior of the emulsions are highly dependent on oil droplet size. For a given oil concentration, the non-Newtonian character and the apparent viscosity increased with decreasing droplet size. The majority of the emulsions showed shear thinning behavior at low shear rates (below 50 s−1) and Newtonian behavior at shear rates above 1000 s−1. These data show that the power law model is insufficient for the whole range of shear rates. A three parameter model needs to be considered. Results show that oil droplet size is the dominant factor in the behavior of emulsions. The influence of mixing intensity and duration while preparing the emulsion and emulsifier concentration on the resulting droplet size were investigated. Pipe flow data were collected for scale-up studies. Data were collected in both the laminar and turbulent flow regimes. This study reveals that careful laboratory testing and scale-up is needed prior to the designing of pipeline systems for the transport of heavy crude oils as emulsions.