Bubbly flows comprise a large number of different flow situations, e.g., dispersed pipe flows, flows in multiphase agitated tanks, flows in multiphase fixed-and fluidized-bed reactors, and typical bubble-column and loop-reactor flows. This paper focuses on bubble-driven flows. These are flow situations were the bubble movement itself is the main source of momentum to the flow field and are often characterized by low superficial liquid velocities, relatively high superficial gas velocities, and no mechanical support of the flow (e.g., agitation). Only vertical flow situations are considered. An overview of the verified forces acting on bubbles is given, and examples of both classical and more recent modeling approaches are shown. This include gravity, buoyancy, centrifugal forces, conventional Magnus and Saffman forces, form and friction drag, and added mass as well as turbulent migration and other instability mechanisms. Special emphasis is placed on mechanisms creating bubble movement in the radial direction. Important literature on the subject with regard to the use of computational fluid dynamics to model gas-driven bubbly flows is reviewed, and the various approaches are evaluated, i.e., dynamic vs steady-state descriptions and Euler/Lagrange vs Euler/Euler formulations. Results from steady-state Euler/ Euler simulations are given and discussed, and the demand for amplified modeling including more accurate and stable numerical solution schemes and algorithms is stressed.

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Statoil recently upgraded its multiphase flow facility in Porsgrunn, Norwayto accommodate live viscous crudes. This facility, which has been operationalsince 1995, enables simultaneous flow and separation tests to be conducted withreal hydrocarbon fluids at realistic temperature and pressure levels. As partof the upgrade, an ESP was installed to study the influence of the ESP on flowand separation under controlled conditions. In this paper selected results are presented of experiments performed withoil/water mixtures with live viscous crude. The oil viscosity in the testsvaries from 30 to 500 cP. The experimental results show that the water cut forthe water continuous flow boundary increases with decreasing oil viscosity. Below this value of water cut, the ESP generates either oil continuous flow orstratified flow. For the dispersed flow both O/W and W/O emulsions weregenerated by the ESP; the classical model on emulsion viscosity gives a goodprediction of the data. Introduction Viscous crudes account for a large fraction of the world's potentiallyrecoverable oil reserves. However, the viscous crude oils have a small fractionof the world's oil production due to their high viscosities which causeproblems in both well and production transport flowline, particularly inoffshore viscous oil fields. Several unconventional methods for viscous crudeproduction in multiphase flowlines have been proposed: preheating of the crudeoil with subsequent heating of the pipeline (Layrisse, 1998; Saniere et al.,2004); dilution with lighter crude oils (Iona, 1978); partial upgrading(MacWilliams and Eadie, 1993), core annular flow with water wetting the wall(Oliemans and Ooms, 1986); and water continuous flow (oil-in-water emulsions)(Lappin and Saur, 1989; Gregoliet al., 2006). All the above-mentioned methodsexperience logistic, technical, and/or economic disadvantages. The implementation of ESP (Electrical Submersible Pump) in the well makes itfeasible to produce and transport crude oil in offshore viscous oil fields. Inthe case of water continuous flow (oil-in water emulsion), it can be veryeffective to transport crude oils with viscosity higher than 1000 cP even incold regions over long distances. One of the key issues of water continuousflow in a long distance transport is the stability of the emulsion. The oildroplets can sediment and form an oil film at the top of the pipe due togravity, which may lead to a significant increase in frictional pressure drop. In terms of hydrodynamics of oil-water two-phase flow, the stability of theemulsion is closely related to the formation of the emulsion, and depends onthe flowrate, droplet size and physical properties of the fluids in theflowline. The emulsion formation of oil-water flow with viscous oil has been studiedmainly in pipe flow or a stirred tank, from which the emulsion viscosity andphase inversion are quantified. The application of these results for theemulsion formation from an ESP has received little attention and is uncertain. Little work can be found on the emulsion formation of viscous oil-water flow byESP in the open literature.