Liquid transport during gas flow transients applied to liquid loading in long vertical pipes

The experimental observations obtained in this work show the liquid re-distribution during changes in gas flow rate. These observations revealed that, after a change in gas rate, the liquid film starts to flow downwards in the pipe, and subsequently, the liquid begins to steadily flow upward at a constant velocity. The experimental data were compared with a numerical model, showing an agreement of ±25%. A pseudo-steady state approach was used to model the vertical gas-liquid flows in this long pipe to describe liquid loading in vertical wellbores. The liquid droplets entrained in the gas core were observed and estimated to be flowing upwards in order to obtain a good agreement between experimental observations and model results, even though the gas velocities were lower than Turner critical velocities. The widely accepted droplet model of Turner says that below the critical velocity, the liquid droplets should be flowing downward and not upwards.