Rationale of Riser System Selection for an FPSO Application

Floating Production, Storage and Offloading (FPSO) system has been used widely in the offshore oil and gas industries worldwide. In recent years, FPSO concept has been deployed in deep and ultra-deepwater field development including West of Africa, Offshore Brazil, and Offshore China. Meanwhile, more and more deepwater risers have been deployed from concept to offshore installation. Compared to other type deepwater floaters (e.g. Spar, TLP, Semisubmersible), the severe motion characteristics of an FPSO makes the riser concept selection and design much more challenges. Other constraints imposed by field reservoir properties (e.g. high temperature\high pressure), disconnection requirements for early production FPSO system, and significant increase in water depth even exclude some riser concepts. This paper presents detailed evaluation of potential deepwater riser concepts applicable for an FPSO. Among the deepwater concepts, steel catenary risers (SCR), flexible risers, hybrid risers have been successfully deployed to FPSO application. In addition, there are also other viable riser concepts for FPSO application including lazy wave SCR, Tension Leg Riser (TLR), Hybrid ‘S’ Riser System (HySR), Hybrid Catenary Riser (HCR), and more to come. The evaluation of deepwater riser concepts for FPSO application is conducted in terms of technical feasibility, design constraints, track records, fabrication, offshore construction, and cost with focus on the existing and field proven riser concepts. Technical challenges and technology gaps are highlighted. The technical feasibility of some of the riser concepts for certain FPSO application has been demonstrated through analysis and calculation. Novel ideas have been generated for particular requirements. Particular attention is paid to the discussion with the application to offshore China. This paper shows the steel riser and hybrid riser are the most viable ones for deep and ultra-deepwater FPSO. Flexible riser and hybrid riser are the preferred solution for FPSO in China.