Accurate prediction of liquid holdup provides important basis for flow pattern identification and pressure drop calculation in wellbores.Slug flow is the most common flow pattern in heavy oil wellbores.High-viscosity flu-ids in the wellbore will exacerbate gas-liquid two-phase slippage,resulting in poor prediction accuracy of existing holdup models applied to high-viscosity fluids.Therefore,a new model for liquid holdup in gas-liquid two-phase slug flow in inclined pipes with different viscosities is proposed.This proposal is based on experimental observations and theoretical derivations.The holdup experiments of slug flow are conducted in a multiple phase pipe flow experi-mental platform,in a test string with an inner diameter of 60 mm.The influence of viscosity on liquid holdup and flow pattern transitions is studied based on the data of slug flow patterns and liquid holdup obtained with different viscosities and different inclinations in the experiments.The study shows that an increase in liquid viscosity will in-tensify the viscous resistance between the liquid phase and the pipe wall,resulting in a rise in liquid holdup.While the effect of viscosity on liquid holdup will change the transition boundaries between slug flow and other flow pat-terns.A new model for liquid holdup in gas-liquid two-phase slug flow in inclined pipes is established.This mod-el is based on the Kora liquid holdup relationship formula and uses mixed-phase viscosity instead of liquid-phase viscosity.The model is validated by experimental and literature data,with confirmed higher accuracy.This re-search can provide technical support for predicting pressure drop in heavy oil wellbores.
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