The extended slug controller introduced in this paper is designed to avoid riser slugging and suppress both start-up slugs and surge waves. Riser slugging is avoided by a pressure controller that keeps the pressure at the riser base constant. Depending on the set point for the pressure controller, this either keeps the process away from riser slugging conditions or stabilizes the unstable operating point that exists at the same boundary conditions riser slugging. Start-up slugs and surge waves are unavoidable, as they are caused by an excess of liquid in the pipeline that needs to be transported out of the pipeline during a rate increase. The controller can, however, smear the waves out using the pipeline as a buffer volume, and by that reduce the peak liquid rates during the transition period. This is done by individual proportional action flow controllers for each phase. The flow controllers reduce the choke valve opening if the flow for the given phase exceeds its set point. The set points for the flow controllers should be set slightly above its nominal rates. The flow and pressure controller that constitute the extended slug controller are combined through a minimum select functionality. This ensures that the controller that asks for the lowest valve opening is active at any given time. This ensures, through the tuning principles introduced in this paper, that the controller effectively limits the flow based on the most critical phase (relative to its maximum allowed production as defined by the downstream production capacity). The minimum select functionality also ensures a bumpless switch between the pressure and flow modes of the controller. The actions and benefits of the proposed extended slug controller are illustrated by simulations from an industrial case study. The case study clearly shows that the controller effectively eliminates riser slugging, and that the peak rates of the start-up slugs and surge waves are significantly reduced by smearing out the waves.
Extended slug control for pipeline-riser systems
Multiphase Production Technology '05, 12 ; 297-311
2005
15 Seiten, 12 Bilder, 1 Tabelle, 10 Quellen
Conference paper
English
A Study of Riser Oscillations Caused by Slug Flows During Subsea Petroleum Production
Springer Verlag | 2020
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