Design and Model Testing of a Shallow Draft Buoy
- Borre Knudsen (Aker Solutions) | Mette Grahl-Nielsen (Aker Solutions) | Bjørn Ågedal (Aker Solutions) | Per Kristian Bruun
- Document ID
- Offshore Technology Conference
- Offshore Technology Conference, 30 April-3 May, Houston, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Offshore Technology Conference
- 4.5.4 Mooring Systems, 4.2 Pipelines, Flowlines and Risers, 4.1.5 Processing Equipment, 4.2.4 Risers, 1.6.5 Offshore Drilling Units, 4.5 Offshore Facilities and Subsea Systems
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The FPSO is the most common of the floating platform solutions. The FPSO isgenerally ship shaped (as the Skarv FPSO installed in the Norwegian Sea) butcan alternatively be a buoy with an axisymmetric shape in the waterline (as theSevan Hummingbird operating in the southern North Sea).
For an FPSO with a ship shape operating in mild environment, weather vaning andheading control is not needed and a spread mooring system can be applied, whichoffers a cost effective concept as turret mooring is not required. An area withsevere weather requires the capability to weather vane and heading control ofthe ship shaped FPSO including a turret mooring system must be applied. For anFPSO with axisymmetric shape in the waterline operating in an area with eithermild or severe environment, there is no need for a turret mooring as the shapeof the buoy in the wave direction will be identical at all time.
The difference between the motions of an FPSO and an FSO, with similar storagerequirements, is limited. For an FSO the production topside would be replacedwith a topside shelter. Going from an FPSO to FSO would for the ship shaperesult in a somewhat reduction in length and breadth while for the axisymmetricshape a minor decrease in diameter would be the consequence. Hence, the FPSOand FSO can be considered as a similar concept with respect to motions.
In order to deliver more cost effective FSO and FPSO concepts Aker Solutionshas over several years investigated the possibility of applying an FPSO or FSOwith axisymmetric shape in the waterline. The first concept within AkerSolutions was the Big Buoy FPSO, which later evolved into the Tentech Buoyform.These concepts were based on the possibility of wet oil storage. With the newenvironmental standards set by the Operators and Governments a requirement fordry oil storage has been introduced which will make these concepts lessacceptable.
In order to revisit the potential cost benefit of applying an FSO with ashallow draft axisymmetric buoy shape (avoid turret mooring) having a dry oilstorage, Aker Solutions has designed a shallow draft buoy with a topsideshelter weight of 1500 tonnes and oil storage requirement of normal shuttlingtankers, as for the Skarv FPSO (for comparison of storage requirements). Asizing of the platform based on these assumptions has been done includinganalysis of the platform performance for moderate North Sea environment throughnumerical analysis. A model test has been performed for comparison purpose withthe motion analysis performed.
Aker Solutions has extensive experience with FPSO design and has over a periodof 20 years delivered designs for various FPSO`s, latest the Skarv FPSO for BP,see Figure 1. The FPSO was installed in 2011 in the Norwegian Sea, west ofSandnessjøen (Norway). All the delivered FPSO designs have been ship shapedincluding a turret mooring system.
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