Deepwater Installation of a Large Capacity FPSO with Large Number of Risers in the Marlim Field
Authors: Bensimon Luiz F. , Lunde Peter A. , Steele Graeme 
Published: October 2008

This paper describes the site installation of a turret moored Floating Production, Storage and Offloading System - FPSO - in 780 meters of water in Campos Basin, offshore Brazil. The FPSO, a 270,000 dwt converted tanker, is the first of a series of two ordered by Petrobras for development of the Marlim Field. An internal bow mounted Turret system, anchored to the seafloor by 8 chain-wire rope-chain combined mooring legs, is used to permanently moor the FPSO in the location while allowing the vessel to freely weathervane. Thirty-five flexible risers, laid in a free-hanging catenary configuration, provide the flow path between the FPSO and the various subsea equipment on the seafloor. This paper describes the installation equipment and procedures employed.

Introduction

In November 1998 Petrobras installed FPSO P-33, the first of two FPSOs provided under one contract, in 780 meters ofwater in the Marlim Field, Campos Basin. The second FPSO, P-35, is being installed in 860 meters water depth. Aside from the water depth, these systems are unique because of the large number of risers installed, 35 for P-33 and 44 for P-35.

The FPSO's process facilities are designed for 50,000 bopd production from subsea wells plus storage from other floating production systems in the field. The operating design life is ten years for the mooring system and twenty years for the rest of the FPSO.

The installation requirements drove the design of the turrets. Because of the large amount of installation work to be done, the turret configuration and equipment were developed to facilitate installation to the maximum extent possible. The system allowed rapid connection of the FPSO to the preinstalled mooring legs, rapid connection of the risers, and an immediate commencement of production.

FPSO, Turret and Mooring Descriptions

The FPSO is a converted Petrobras 270,000 DWT tanker provided to the prime contractor, Hyundai Heavy Industries. The turret is installed in a moonpool located fore of the cargo tanks (see Figure 1).

The diameter of the lower end of the turret, 12.0 meters for P-33 and 13.5 meters for P-35, is governed by space requirements for the mooring leg hawses and the required spacing of riser connection points. The sloped riser I-tube configuration allows a smaller diameter one piece roller bearing to be installed at the top of the turret. The main bearing is mounted on a spherical elastomeric support above the main deck level to react vertical and upper support lateral loads from the turret. Lateral loads acting at the lower end of the turret are reacted by a series of journal bearing pads located near the keel of the vessel. Above the main bearing is the superstructure, which is fixed to the turret and is geostationary. The superstructure contains installation and chemical injection equipment on its lower deck and supports manifolds and well control equipment on its upper decks. At the top of the superstructure is mounted a twelve pass fluid swivel stack. The overhead service structure, mounted on the vessel, drives the outer rings of the fluid swivels, supports piping and provides access to the turret superstructure.