ABSTRACT

In this work, we present a methodology for characterising slugs based on OLGA slug-tracking module. A major challenge in slug analysis is the determination of the hold-ups in the liquid and bubble areas of the slug, which are key parameters in estimating the slug load response of subsea structures. The study is based on Egina, a new West African deepwater field development project, using fully characterised reservoir fluid properties and a full-field subsea network model including the wells and their trajectories. The field will be developed through a Floating Production Offloading and Storage facility, in an average water depth of 1550 m. The reservoir is characterised by fluids of approximately API 23-27 and average GOR in the range of 100-150 Sm3/Sm3.

Statistical distribution of the slug parameters, including slug unit length, mean slug density, mean slug frequency, and mean slug velocity, were obtained by detailed analysis. In addition, careful operational mitigations were implemented resulting in significant reduction in the slug frequency and density variations. The results suggest that topside choking to increase flowline back pressure is a very effective mitigation method for hydrodynamic-dominated slugs.

The methodology developed in this work may be applied during engineering studies to define slug load cases for riser-base spool fatigue design. The work is also of importance in dynamic slug control in the operation of existing fields either manually or automatically via the OCWR modules.

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