Independent Design Verification of SCRs for Ultra Deepwater IHF Development

Steel catenary risers (SCRs) have been selected as the production riser solution for the Independence Hub Facility (IHF) in water depth of 8,000 ft in the Atwater Valley region of the Gulf of Mexico. This is the deepest water depth for SCRs to date. Initially, the gas production riser system consists of two 10-inch SCRs and four 8-inch SCRs attached to a deep draft semisubmersible as the host platform. Technip was selected to conduct independent engineering design verification for the production SCRs to verify the feasibility of their design and to identify potential design problems. This paper describes the design extreme challenges and uniqueness due to the ultra deep water, in addition to presenting the design verification methodology, procedure, selection of hydrodynamic parameters, pipe soil modeling, computer modeling, findings, and technical discussions. ABAQUS was the primary tool used for this design verification in association with other in-house riser analysis tools. Comparisons were made with the results from Flexcom. The independent verification analysis included storm analysis, motion fatigue analysis, semi-submersible heave-induced vortex induced vibration (HVIV) fatigue analysis, semisubmersible vortex induced motion (VIM) fatigue analysis, and riser interference analysis. Sensitivity study was carried out to demonstrate the accuracy of the simulation results and the robustness of the design. The independent verification shows that the riser top design is governed by the strength criterion due to large tension force. Fatigue governs the riser touchdown point (TDP) region, especially for the larger diameter SCRs. Among fatigue damage sources, fatigue caused by semisubmersible motion and VIM dominate. This paper concludes that the IHF SCR design meets the API RP 2RD design code requirements.