Gas-Liquid Hydrodynamics during Liquid Displacement by Gas in Up-Hill Pipeline

Abstract

Mobile pipelines are the most efficient and reliable way to transport large quantities of oil over long distances in warfare, rescue and disaster relief. The oil in the pipe must be discharged and recovered when the oil transfer task is completed, usually via gas cap evacuation. Gas cap evacuation is the main method to evacuate mobile pipelines. During evacuation, due to the influence of topography, working conditions and gravitational forces, the oil in an up-hill pipeline is gradually deposited in the low-lying part of the pipeline to form a liquid, resulting in the incomplete emptying of the pipeline which directly affects the recovery efficiency of the pipeline. Focusing on the analysis of the gas carrying oil flow process in an up-hill pipeline during the evacuation of gas displacing oil in the mobile pipeline, the tail and head of the liquid accumulation were analyzed, and the liquid accumulation flow model was established based on the gas–liquid two-phase stratified flow theory. This model was used to analyze the flow law of the accumulated liquid under different pipe inclination angles, initial accumulation thicknesses and pipe diameters. It was found that the stagnant oil in the pipeline is carried by the gas flow into the upward tilting pipeline due to the influence of the axial gravity force of the pipeline. The gas flow can be divided into three phases: the initial discharge stage, the oscillation stage and the final discharge (reflux) stage.