Tanker based Floating Production, Storage and Offloading Systems (FPSO's) are being used in increasingly deeper waters. The use of spread moored tankers for deep water applications is widely accepted to be a viable and cost effective solution for developments in areas with relatively benign environmental conditions (e.g. West of Africa). With the constant drive towards deepwater floating production, the costs of the riser and mooring systems are a significant percentage of the overall field costs and it is essential to minimise these costs. The concept and design presented in this paper involves combining the risers and moorings into a single integrated system, which offers the potential for very large cost savings. The concept combines standard steel wire mooring components with a hybrid type riser system. The hybrid system comprises steel catenary risers (SCRs) connected to a subsea buoy with flexible jumpers located between the buoy and the vessel. The system utilises the full potential restoring force capability of the SCRs which are positioned in tandem with mooring lines of minimal length. The subsea buoy located just below the wave zone provides an interface to which all mooring and riser components of the combined system are connected. The system is both feasible and cost effective for a spread moored FPSO in a largely directional environment. This concept offers significant benefits over the independent riser and mooring systems, in terms of: 1. Large economic savings in the mooring system. 2. Optimised design conditions for both steel and flexible risers. 3. Reduced vessel offsets (allow easier access to the field for drilling and workover vessels). 4. Large reduction in the seabed area required for the riser and mooring systems. 5. Ability to make maximum use of weather directionality effects.
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