We consider the apparent roughness and increased pressure drop associated with the presence of a thin liquid film between the gas and the pipe wall in a two- or three-phase separated gas-liquid flow. The main objective is to improve the pressure drop predictions for near-horizontal gas-condensate flows with low liquid loading. However, in this paper, we focus on vertical (fully symmetric) annular flow to isolate the effect of the liquid film. To support the model development, SINTEF conducted experiments in a 4-inch ID 50 m-high riser at the Tiller test facility in Norway. The data revealed interesting and unexpected phenomena for high water fractions. Nevertheless, a new model for the film roughness based on dimensional analysis and simple but fundamental physics is able to give results in very good agreement with the data. The new model also provides a robust estimate of liquid entrainment. All liquid in excess of that which can flow in the liquid film is entrained into the gas phase through the action of interfacial turbulence.


The Tanzania Gas Project aims to exploit reserves located offshore from Tanzania in East Africa. The narrow operational envelope associated with the extreme water depth underlines the importance of accurate flow simulations for design and production. A large data set was sampled at the Tiller high-pressure test facility in Trondheim, Norway in 2013 and 2014, to support the modelling of liquid accumulation in the Tanzania field (Holm (1); Kjølaas et al. (2); Biberg et al. (3); Staff et al. (4); Nossen et al. (5)).

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