SCR with FPSO Design Challenges Subject to Complex Bi-Modal, Bi-Directional Environment in Ultra-Deep Water

This paper discusses steel catenary riser (SCR) design challenges subject to complex bi-modal and bi-directional seastates offshore West Africa in ultra-deepwater (2,600m). Metocean data is key to determining the design of SCRs. As offshore exploration continues in remote regions and deeper water depths, it is very important to obtain accurate and comprehensive environmental data for the field. Different locations around the world have distinct offshore environments such as hurricanes, typhoons, swells and squalls with seastates exhibiting a varying range of frequency content. The work in this paper describes effects of multiple seastate modes on the riser’s performance. The risers evaluated are 10 inch production and 18 inch export SCRs connected to a spread moored FPSO. Riser fatigue was particularly challenging given the unique environment consisting of up to four wave modes in a single sea-state. Several sensitivities were performed to improve the fatigue performance of the risers. Finally a feasible riser concept was selected which met all of the project design requirements. Work showcased in this paper will address the challenges of placing steel catenary risers in remote deep water fields with relatively unfamiliar metocean conditions. Several sensitivities are performed with the riser properties, platform motions and environmental data which help to reduce design conservatism and better understand the fatigue response of SCRs connected to a spread moored FPSO.