An approach to model slug flow in pipelines and pipeline-riser systems is presented which is based on a transient Lagrangian formulation. This method is particularly useful for slug flows approaching the end of a pipeline or for predicting the influence of a riser pipe to the production system. The flow is modelled by considering a series of slug units, each consisting of a "liquid" slug and its associated "gas" bubble, being continuously introduced into the system at a fixed location considerably remoted from the system outlet. The flow parameters are predicted as the slugs traverse the system. There are of course interaction effects between successive slug units and outlet effects (disturbances) can be transmitted upstream. Liquid hold-up in the "liquid" slug and "gas" bubble is accounted for as gas compressibility. It is assumed that there is no mass transfer between phases. To validate the approach used, the model was tested against a homogeneous flow condition with a steady air - water flow system. Results are also presented for trains of slug units negotiating the pipeline riser pipe system.
The presence of slug flow in a transportation pipeline can be particular troublesome. This steady state models which consider, to a greater or lesser extent, the details of the flow of individual slugs. However Brill et al [5) have presented correlations based on anaIysisof data obtained from the Prudoe Bay pipeline in Alaska. In relatively short horizontal lines it has been established that for steady conditions liquid slug length of the order of20 -25 pipe diameters can be expected (normal slug flow). However, in long undulating pipeline - vertical riser system, large slugs have been shown to occur. When slug lengths are greater than the height of the riser this is often termed as severe slugging.
