Restart model for a multi-plug gelled waxy oil pipeline

A numerical model has been developed to simulate the restart behaviour of pipeline containing gelled waxy oil. The model takes into account the compressible, multi-phase and multi-plug flow characteristics of the gelled oil at start-up. The pipe is initially filled by the gelled oil in the form of plugs separated by pockets of gas. Displacement of the gelled oil is achieved by pumping in another fluid under constant applied pressure. The simulation results obtained show that the initial gas pressure and the location of the gas segment influence the flow of the downstream oil plug, but has little effect on the flow of the upstream oil flow and the clearance time. The length of the gas section has different effects on the oil flow rates and clearance time depending on the initial liquid hold up present in the pipe. The model is robust and insensitive to the specific constitutive model assumed for the gelled oil. It appears to produce a more realistic prediction of the restart flow than other previous models based on restrictive and simplified assumptions.