Severe slugging and unstable flow in an S-Shaped riser has been investigated in threeresearch themes - experiments, criterion modelling and transient code modelling.A series of experiments were carried out on the Cranfield University Three PhaseFacility and Riser Rig using a 10 m high riser over the pressure range 2,4 and 7bar(a). The collected information was used to characterise the unstable flows in termsof pressure cycling, riser liquid inventory and fluid production characteristics. Fromanalysis of the flow behaviour, it was found that in terms of slug characteristics,transitional severe slugging and oscillation flows are as potentially problematic as`classical' severe slugging. This is due to the magnitude of peak flow in excess of theaverage fluid throughput in the riser and the size of the liquid slugs generated.A criterion for the occurrence of unstable flows in an S-Shaped riser was developedbased upon considerations of bubble penetration at the riser base. This proved to besuccessful at predicting the experimental results from this work and an independentsource.Comparisons were made between the experimental results and a transient code. Thecode could predict the occurrence of `classical' severe slugging however the detailedcharacteristics of the experiments were not predicted by the code. The results fortransitional severe slugging and oscillation flow showed further differences betweenthe code prediction and the experiments. Drawing all simulation results together itwas concluded that the prediction of pipeline behaviour and the propagation of flowregimes local to the riser base and in the curved riser pipe were significant sources oferror in the simulation.
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