Case Study - An FPSO with DP for Deep Water Applications

In the coming years, there will be a growing demand for Floating Production and Storage Units (FPSOs) for ultra deep waters (greater than 2000 m [6,000 feet]). In the Gulf of Mexico, the technical and economical limitations inherent to other type of concepts, the lack of pipeline infrastructure in such deep areas, and the wide acceptance of the FPSOconcept by Shelf Authorities will accelerate this process.

One of the most critical issues in the design of FPSOs for ultra deep waters will be the selection of the most cost-efficient station keeping system for the specified operational requirements. Standard solutions based on internal turret and thruster assisted mooring systems are already being offered by the industry. However, beyond certain water depths, the technical and economical constraints associated with the use of mooring systems may favour other concepts potentially more attractive and cost-efficient, such as a fully dynamically positioned FPSO (DP-FPSO). This concept marries state-of-theart FPSO technology and latest generation drill ship technology for dynamic positioning and operation in ultra deep waters. This system can either be utilised as an early production system or as a full-fledged field development solution. The areas most suited for this application will be the Gulf of Mexico, Brazil and West Africa.

The paper describes a joint study undertaken by the various companies represented by the authors to develop a design for a fully dynamically positioned FPSO for ultra deep waters. The various technical challenges and regulatory issues for a fully DP-FPSO will be identified and solutions to them provided. Detailed design information on the vessel design, the DP thruster, Power Generation and control systems, and the disconnectable turret and riser system shall be provided for a hypothetical field development in ultra deep water. The system performance shall be illustrated by the results from a comprehensive study involving state-of-the-art computer simulations and model test program. Results and conclusions from a reliability and safety study performed on the system shall also be presented, as well as those from a thorough power consumption analysis for the geographical areas of interest. Finally, a comparison is made between components associated with the stationkeeping system of the DP-FPSO and a conventionally turret moored FPSO, to provide input for CAPEX/OPEX estimates which in turn can be used to identify the range of water depths and field development scenarios for which the DP-FPSO is commercially feasible.