Gas-condensate pipelines with very low liquid drop out (Usl>0.005 m/s) are characterised by low rates of liquid accumulation in upward inclined sections. One particular feature of such flows in moderate upwardly inclined pipes is that there exists a region where the liquid holdup increases steeply with decreasing flow rate. To the authors knowledge, only very few data are presently available for these kind of systems which implies that present multiphase flow models to little extent have been tested for accuracy in this respect.

The main objectives with the work described in this article have been to search experimentally for the regions with liquid holdup discontinuities, quantify the condensate-water slip at low gas velocities and compare the data against existing models. Particular emphasis has been on obtaining data on how the presence of different hydrate inhibitors influences the holdup gradients and the condensate-water slip ratio. The experimental data have been collected in the Hydro high pressure, multiphase flow loop in Porsgrunn, Norway, which includes a 3" test section with a total length of 200 m. A recombined hydrocarbon system was used, including gas and condensate from an onshore terminal. Fresh water and hydrate inhibitor were added, and the experiments were conducted at 75 bar pressure and a temperature of 0 °C. Experiments were conducted at +1 and +5 degree inclination angle with three different water cuts, 0, 15 and 85 % with a constant superficial liquid velocity of 0.001 m/s. The paper presents data for steady state conditions, including liquid and water holdup, flow pattern and phase distribution. In addition, comparisons with steady state OLGA2000 are presented and discussed with respect to pipeline conditions

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