Characteristics of High Viscous Oil-Gas Flow in Downward Vertical Pipes

Abstract

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 127 to 586 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. Comparisons with available mechanistic models and simulators are reported. Existing mechanistic models dominantly predicts flow pattern as slug flow, and over-predicts average liquid holdup especially low liquid viscosity condition. To ensure applicability of existing annular flow model, experimental data of upward flow for high viscosity oil. As a result, closure relationship is affordable for vertical upward flow due to its low liquid entrainment fraction, while it shows disappointing prediction performance in vertical downward flow.