Applications of Large Diameter Steel Lazy Wave Risers for Production Systems in Deepwater Norway

June 2017
R. Shankaran, M. Lopes, H. Howells

In the current low oil price market, innovative low cost solutions are necessary for development of new fields and late life recovery from existing fields. Steel Lazy Wave Risers (SLWRs) provide low cost alternatives to flexible risers and offer flexibility during design and late life for Floating Production Systems (FPS) in deepwater North Sea. While flexible risers are limited to a maximum of 16” inner diameter, steel risers are qualified for pipe diameters of over 24”, which can help reduce the number of risers tied-back to the FPS and lower development costs.

Deepwater fields in the North Sea greater than 400m water depth have traditionally been developed using flexible risers. The steel lazy wave riser (SLWR), a variation of the steel catenary riser (SCR) with added buoyancy near the touchdown point at the seabed, have recently been deployed in the GoM and Brazil for deepwater applications. Due to simplicity of design, good track record and qualified suppliers, fabrication and installation methods for SCRs, SLWRs have become a logical extension of the SCR for more severe environments and vessel motions. Harsh North Sea environments result in high FPS motions. Buoyancy installed on the SLWR helps decouple vessel motions at the riser touchdown, which ensures that the required strength and fatigue performance can be achieved.

Development of a 24in SLWR for a North Sea application in 850m water depth is discussed. The strength and fatigue response of the resulting riser arrangement is evaluated. The advantages and disadvantages of SLWR North Sea applications are assessed and costs for flexibles and SLWR’s compared.

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