Evolutionary Developments Advancing the Floating Production, Storage, and Offloading Concept

Abstract

Summary Tanker-based floating production, storage, and offloading (FPSO) systems have been in operation since Aug. 1977, when a single-well FPSO facility was put into production by Shell Espania in the Mediterranean. The overall operational experience with this system at this field is reviewed, with special attention to the wireline work over facilities, which have proved very satisfactory. A subsequent evolutionary step, a FPSO system accommodating multiple wells, necessitated development of a multi bore fluid swivel. A design program for this swivel was initiated in 1978; a prototype was built and full-scale testing finalized in 1980. A summary of the test results is presented. Simultaneously with the multi bore swivel development, detailed engineering for an eight-well FPSO unit was begun. This system includes gas-lift and water-injection capabilities. Provisions for through-flow line (TFL) well work over can be incorporated. The detailed design is reviewed, as well as the latest development whereby the FPSO concept has been adapted to the North Sea environment. Introduction and Background Stationary offshore terminal facilities using former trading tankers were employed by the oil industry as early as 15 years ago. Initially, a tanker was connected by conventional hawsers to a catenary anchor leg mooring, where it served as a combination buffer storage vessel and mooring platform for shuttle tankers. Poor operational experience, low survival characteristics, and high maintenance costs stimulated the development of the single-buoy storage (SBS) system employing rigid arms for permanently mooring the vessel to the buoy. The first terminal of this type became operational in 1973, and it and half a dozen similar terminals have served efficiently for many years. In Aug. 1977 a further step in the evolutionary process was taken with the startup of a tanker-based, rigid-arm single anchor leg storage (SALS) floating production facility at the Castellon field in the Mediterranean off-shore Spain. This system incorporates conventional separation equipment on the vessel for producing from a single subsea-completed well. A second similar facility also producing from a single well was installed in 1980 at the Nilde field in the Sicilian Channel. Recognizing the need for testing and producing independently from two or more wells and injecting into wells, Shell instigated a program in 1978 to develop a high-pressure, multi flow-path swivel for interfacing the weathervaning vessel with the nonrotating buoy or riser. In Aug. 1981 a facility went into operation at the Cadlao field offshore Philippines using this new high-pressure, multi flow-path swivel producing from two subsea-completed wells. A fourth FPSO facility capable of accommodating eight wells went into production at the Tazerka field onshore Tunisia in late 1982. Table 1 provides a recap of these four FPSO facilities. The Floating Unit While a semisubmersible platform is usually in a fixed mooring pattern, a tanker-based floating production facility is normally designed to weathervane, thus introducing the necessity for mechanical and fluid swivels. Both types of swivel must be engineered carefully and constructed to precise specifications. JPT P. 695