The Effect of Ship Motions on FPSO Topsides Design

Abstract

Abtract A vast experience on design of gas and oil processing facilities baaed on fixed platforms exists all over the world. A development of the last yews is to place the facilities on a floating tanker which serves as storage unit as well as foundation. The so-called Floating Reduction and Storage Units are usually "weather-vaning" around the turret. Wind, waves and current cause motions of the FPSO and the various loading and ballasting conditions result in semi static inclinations. The various motions and barge conditions have an effect on the topsides processing facilities. In this paper the effects on the topsides layout, the design of process equipment and the detailed structural and piping design of the topsides are presented. Introduction The Guillemot and Teal project was started in January 1994when Shell Expro, who operate in the North Sea on behalf of Shell UK and Esso UK, awarded a contract for the lump sum turnkey delivery of the floating production and storage facilities to Single Buoy Moorings Inc (SBM), Fribourg. This company awarded a similar subcontract for the barge and the topsides to respectively Mitsubishi Heavy Industries (MH1), Nagasaki and Stork Protech Schiedam. Design of the turret would be executed by the Single Buoy Moorings lnc in the offices in Monaco. At a later stage in the project both Single Buoy Moorings Inc and Stork Protech awarded a contract for the fabrication and installation of the turret and topsides to AMEC Energy and Process Ltd, Newcastle. The main purpose of the FPSO is to produce dead cru& for export via shuttle tankers, to treat and export associated gas into the Fulmar Gas Line, to treat produced water prior to disposal overboard and to treat and inject seawater for water injection. The facilities will be installed on a newly built barge of approximately 132,000 tones dwt, The FPSO will be permanently moored by means of an integrated turret mooring system which will support the transfer facilities for well fluid and produced fluid streams to and from the FPSO. This paper describes the facilities provided on the Anasuria FPSO, the lay-out of the topsides equipment on the FPSO deck, the influence of the "weather-vaning" and other motion effects on the topsides lay-out and on the design of process equipment. Furthermore, the influence of FPSO movements on the structural and piping design is described The paper concludes with some lessons learned and recommendations on the basis of gained experience, Relevant Barge Movements The FPSOis subject to various types of motions and conditions arising from environmental forces, from barge loading and ballasting conditions and from operating procedures. Therelevant types of movements and conditions are categorised and described in some detail below, Weathervanistg. Weathervaningis the rotation of the barge around the fixed moored turret at the bow. Weathervaning is the result of environmental forces exerted by the wind, the waves and the currents. The turret allows 360 degree weathemirring. Weathewaning is a complex phenomenon, in which also the draft conditions of the barge play a role.