Full Field and Early Productions Ultra Deep Waters: The ‘DP-FPSO’ and ‘DP-EFPSO’ Concepts
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]), as evidenced by the large number of deep water FPSOs being considered for West Africa, Brazil and possibly the Gulf of Mexico. Several standard solutions for FPSO systems exist - turret moored FPSOs, turret moored FPSOs with thruster-assistance, and spread-moored FPSOs for benign, directional environments. However, beyond certain water depths, the technical and economical constraints associated with the use of passive mooring systems may favour a fully dynamically positioned FPSO. This system can either be utilized as an early production system designed to operate on many fields, or as a full-field development solution with service life up to 25 years. The areas most suited for this application are offshore West Africa, Brazil and the Gulf of Mexico. The paper describes a joint study undertaken by the various companies represented by the authors to develop designs for fully dynamically positioned FPSOs for ultra deep waters. Two systems have been developed - a full-field development solution for the Gulf of Mexico (DP-FPSO), and an early production system for West Africa (DP-EFPSO). The various technical challenges for both systems have been identified and solutions to them provided. The differences in environment and operation of the two systems are discussed. Results from computer simulations and model tests are also provided to illustrate system performance in mild and harsh environments, and to study the performance as a function of control strategy.