There is a recent interest on the production of medium to heavy oils in offshore environments. The use of multiphase pumps located in platforms has been proposed to ensure the transport of the fluids to the shoreline facilities. After the platform, the multiphase flow stream is redirected to the sea floor using a down comer. Thus, the understanding of the viscosity effect in downward vertical flow becomes critical for the system design.
An experimental study on the viscosity effect has been carried out using a 2-in. ID multiphase flow facility. The viscosity of the oil ranged from 122 to 560 mPa s. The superficial gas and liquid velocities varied from 0.3 to 7 m/s and 0.05 to 0.7 m/s, respectively. Flow pattern, pressure gradient and liquid holdup data were acquired and compared with previous air-water experiments. Three different flow patterns have been identified based on visual observations and capacitance sensor readings. Flow pattern, superficial velocities and viscosity effects on pressure gradient and liquid holdup are presented. Finally, comparisons with available mechanistic models and simulators are reported.
A large number of experimental and modelling studies on gas-liquid two-phase flow have been carried out owing to its importance in industrial applications. In petroleum industry, relatively few investigations in vertical downward two-phase flow have been reported as compared with horizontal and vertical upward. Downward flow has been traditionally encountered in relatively short length of pipes in offshore production operations. However with the growth of deep-water production, vertical down-comers from platforms to the seafloor may have lengths of several thousand feet. Accordingly, more accurate prediction of pressure drop and liquid holdup over these lengths becomes significantly important.