Design Challenges for the K2 North Project Steel Catenary Risers

The K2 North project located in Green Canyon Block 518 (GC518) in the Gulf of Mexico ties-back four subsea oil wells to a host facility (Marco Polo TLP) in the GC 608, in approximately 4300 feet water depth. The plan is to tie-back the subsea wells via dual pipe in pipe insulated flowlines through an insulated production manifold. Each well will connect to the manifold via insulated flowlines or insulated flowline jumpers. The flowlines connect to the host facility via Steel Catenary Risers (SCRs). These SCRs consist of heavy wall 6.625-inch pipe with wet buoyant insulation necessary to minimize the impact of top tension loads on the host facility. This paper discusses the key aspects of the design of the SCRs, and highlights the importance of a prudent engineering approach to deliver the optimal riser solution. These include the early identification of the potential for interference between the two project risers, and with the third party risers and adjacent TLP tendon. This design aspect was exacerbated by the weight limit imposed on the tieback risers, and by the use of VIV suppression strakes suitable for the selected installation method. The paper describes the solutions developed to avoid interference relating to riser layout and configurations and selection of wet insulation coating system. The paper also presents the qualification tests planned and conducted to prove the suitability of the wet insulation coating system for the S-lay installation method. K2 North (GC518) risers will be the first application of this coating on SCRs. The paper also demonstrates the importance of allowing sufficient margin in early stage of design to accommodate future changes as design matures, especially for fast track projects like this one. The K2 North SCRs represent typical subsea tieback scenarios in the Gulf of Mexico. The experience gained during the engineering design of these risers is therefore of significant value with regard to assisting in safe and economic design of such future developments.