Trapped water displacement from low sections of oil pipelines

The study is motivated by the problem of pipeline corrosion due to water accumulation at low spots. Lab-scale experiments were conducted to identify the critical conditions required for the onset of water displacement by oil flow from a low horizontal section into an upward inclined section of the pipeline. Two test loops with pipe diameters of 27 mm and 41 mm I.D. with diesel flow were used. Water withdrawal from tapping valves distributed along the up-hill section enabled to follow the water displacement for oil flow rates exceeding the critical value.A model for predicting the water displacement by the oil flow, which is based on the formation of a water plug in the lowest (horizontal) section, is suggested. The predicted amounts of water withdrawn from the tapping valves favorably compare with the experimental results. Considering other competing mechanisms, up-scaling to larger pipe diameters is examined. The analysis indicates that water plug formation appears to be the controlling mechanism for water displacement also in larger pipe diameters encountered in field operations.