Liquid displacement from lower section of hilly-terrain natural gas pipelines

Offshore gas fields are challenged by liquid accumulation at lower sections of the hilly-terrain pipelines. To enhance flow assurance, complete purge-out of the liquid by the gas flow is desired. Experiments in atmospheric air-water system are used to determine the critical flow rates leading to purge-out. Several flow patterns are observed as a function of the up-comer inclination angle, gas flow rate and the initial liquid volume. These flow characteristics and the critical flow rates are adequately predicted by 2D numerical simulations. A simple scaling rule is suggested for using low-pressure data for evaluating the critical gas flow-rate at high-pressures typical to natural-gas pipelines. The validity of the scaling-rule predictions is verified by the simulation results. The gas flow-rate for the complete purge of liquid is found to be independent of the initial volume of the trapped liquid, however, increases with the up-comer inclination.