Abstract:
Severe slugging and unstable flow in an S-Shaped riser has been investigated in three
research themes - experiments, criterion modelling and transient code modelling.
A series of experiments were carried out on the Cranfield University Three Phase
Facility and Riser Rig using a 10 m high riser over the pressure range 2,4 and 7
bar(a). The collected information was used to characterise the unstable flows in terms
of pressure cycling, riser liquid inventory and fluid production characteristics. From
analysis 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 the
average 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 developed
based upon considerations of bubble penetration at the riser base. This proved to be
successful at predicting the experimental results from this work and an independent
source.
Comparisons were made between the experimental results and a transient code. The
code could predict the occurrence of `classical' severe slugging however the detailed
characteristics of the experiments were not predicted by the code. The results for
transitional severe slugging and oscillation flow showed further differences between
the code prediction and the experiments. Drawing all simulation results together it
was concluded that the prediction of pipeline behaviour and the propagation of flow
regimes local to the riser base and in the curved riser pipe were significant sources of
error in the simulation.
