Flexible risers are key components of floating production, particularly in harsh environmental conditions where the riser must deal with substantial vessel motion. Throughout their operating lives, well characteristics change over time; changing flowrate, pressure, temperature, gas oil ratio and water cut may have a large impact on existing facilities. Thus it is important to be able to predict how the flow delivery from the riser changes over time. Riser induced severe slugging has been a subject of research since the eighties (Taitel (1986) Schmidt et al (1981) and others). Their efforts were concentrated on vertical risers. The necessary conditions for severe slugging were identified which are valid to risers of different shape. The behaviour of flexible risers has been studied experimentally by Tin (1991). For an S-shaped riser, the gas trapped in the downwardly inclined section of the riser made the overall behaviour more complex. More detailed and systematic studies have been carried out at Cranfield University as part of the Transient Multiphase Flow Programme (TMF) (Montgomery & Yeung (2002)). A vast quality of data has been collected.
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