Tanker-based floating production systems have been proven feasible for offshore field development. However, further work is needed to ensure these facilities are economically competitive and technically sound. The presented work, based on past experience and lessons learned, provides a basis for the selection and design of cost-effective monohull floating production systems. Major issues addressed, are the cost of sound designs and their sensitivity to design variations. Important design parameters of these systems are analyzed and available design methodologies are outlined. The presented analysis is limited to the surface unit and it's mooring system. Subsea and riser systems are not discussed. Results presented are applicable regardless of water depth, field production rate or location and should serve as an aid to owners, operators and designers of production tankers.
The first tanker-based production system went into operation in 1977. Since then, the development of these specialized floaters has progressed rapidly. In the first years of development the production tankers where simply transiting ships dedicated to this new service. Their hull forms were not changed markedly. Only processing, mooring and a few specialized facilities were added. Apart from local strengthening of the hull at the vicinity of the processing and mooring facilities, no major hull modifications were done. This keeping with traditional transiting tanker design, could be expected. It made use of the abundance of tankers available for such a service and provided for a smooth development of existing technology.
In 1986 the first purpose built production tanker went into service. Currently, a number of purpose designed vessels await construction and additional conversions have been proposed. Tankerbased production units are being used in hostile environments, deep water depths and remote locations. They are useful for small field development, extended reservoir testing and multi-location field production. One can then wonder about the direction of future production tanker development. What will be the effect of ever changing economic conditions on their design? How can one decide whether an existing tanker should be converted or build a new unit? In either case, upon which basis should the unit be designed?
It is difficult to discuss the economics behind the development of tanker-based systems using generalities. Each field development scheme has a solution unique to it. However by examining these issues with greatest cost implications, general guidelines for the development of sound designs can be provided.
The cost of a production tanker can amount to one third of the cost of a typical offshore field development effort. Structural and outfitting costs can equal 70 percent of the initial cost of the tanker and the initial cost can vary about 20 percent between converted versus new built vessels. Therefore, it is imperative that the correct type, size and strength of vessel be selected.
