FPSO's Today: What is the Optimum Concept?

ABSTRACT FPSO technology over the past years has rapidly evolved from tanker based units with classical mooring systems to purpose-shaped new built vessels equipped with DP assistance, sophisticated permanent turrets or disconnectable mooring systems. FPSO's cover today a much wider range of applications than a few years ago, and are contemplated for ever more demanding field developments. Selecting the optimum FPSO concept at the beginning of a project is therefore a new step in the early phases of conceptual engineering. This paper describes the main design parameters of current FPSO projects, and evaluates the significance of their influence on the overall design. Several guidelines and insights are provided to help in selecting and combining together technical options available for specific field development cases. The detailed engineering, execution and operational experience gained on recent projects and actual realisations are largely called upon so that pragmatic considerations and recommendations can be suggested for achieving optimized FPSO configurations in a wide range of applications. WHAT IS AN FPSO? The "FPSO" acronym stands for: Floating Production, Storage and Offloading, which well defines the systems in question. The FPSO is one branch of the growing family of Floating Production systems, and differs from its colaterals by its capability to store and export oil in addition to producing from an offshore field, all in a single unit. While loading terminals or export pipelines are generally required with Floating Production systems, oil is directly offloaded to export tankers with an FPSO. Although not reflected in its name, facilities upstream of the production equipment can also be integrated with the FPSO system, including subsea well control, subsea flowlines, risers and manifolding. GENEALOGY (ORIGIN AND EVOLUTION) The ancestor was pioneered in 1976 by Shell in their Castellon Field offshore Spain. A 60,000 DWT tanker, "lldeFonso Fierro", was converted to an FPSO, producing oil from a single subsea well (Photo 1). It was soon followed by a twin in the Nilde Field offshore Sicily for Agip. The FPSO concept then evolved to handle production from several wells (Cadlao, Tazerka, Garoupa) and with more and more comprehensive process installations (Hondo). While it was favoured for developing several marginal fields in mild environments such as offshore west Africa, it also adapted itself to ever more demanding requirements, such as the threat of typhoons in south east Asia, with disconnectable mooring systems (ACT's Nan Hai FaXian, Photo 2), or to the stringent conditions of the North Sea with newbuilt units (Petrojarl 1). If a single picture of the whole FPSO family was possible today, no doubt it would be extremely colourful and contrasted. In the eighties, two factors contributed to the initial growth of FPSO's both in maturity and number:the availability of relatively young tanker tonnage at very low prices,the sustained development of swivels, flexible risers and subsea well technologies. However, the emergence of FPSO's as a standard way of developing a field is fairly recent, and this is probably due to the extension by the Oil Companies of the boundaries for the development of new fields.