Espirito Santo: Design and Operational Expereince of the Use of Steel Risers on a Turret-Moored FPSO

Abstract

SBM Offshore; Svein Haaheim, Shell Brasil Petroleo; and Eric Martineau, SBM OffshoreThe centrally located FPSO facility is the Espirito Santo. The BC-10 joint venture charters the FPSO facility from SBM Offshore jointly with MISC under a long-term lease and operating contract.A unique feature of the BC-10 development is the use of steel lazy-wave risers (SLWRs) in conjunction with an internal turretmooring system. This is the first use of SLWRs in the industry, and the first time a steel-riser system of any configuration has been used with an internal turret-mooring system. After more than 5 years of operational experience, the integrity of the turret and riser system has been demonstrated in field conditions. The intent of this paper is to describe the impact of the use of SLWRs on the turretmooring system, and to report the in-service inspections carried out to verify the ongoing integrity of the riser system. Mooring-System SelectionTurret-moored floating production, storage, and offloading (FPSO) vessels and spread-moored FPSO vessels are both operating offshore Brazil, but the spread-moored systems rely on shuttle tankers with dynamic positioning (DP) to ensure sufficient availability of SummaryThe floating production, storage, and offloading (FPSO) facility Espirito Santo, located offshore Brazil in the Parque das Conchas (BC-10) field, is the world's first turret-moored FPSO facility to use steel risers for fluid transfer. The FPSO facility is moored in a water depth of 1780 m, and the internal turret incorporates a total of 21 riser and umbilical slots. The steel risers, which are in a lazywave configuration, were pulled into the turret through inclined I-tubes. Clamps at the top of the I-tubes retain the risers, thus transferring axial loads from the risers to the turret. A clamp casting welded at the bottom of the I-tubes houses a stopper arrangement designed to transfer shear forces and moments from the risers to the turret.The FPSO facility began oil production in July 2009, and now has more than 5 years of operational experience. During this period, inspection of the riser system and the associated flex joint has confirmed the integrity of the design, giving further confidence in the use of steel risers in turret-moored systems.This paper summarizes the basis for selecting steel risers for the development, how the risers and umbilicals interface with the turret, and the impact of the riser choice on the turret design. The in-service inspection of the riser system is described, and the results are reported.