Espirito Santo: Design and Operational Experience of the Use of Steel Risers on a Turret-Moored FPSO
The 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 lazy-wave 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.
The Parque de Conchas (BC-10) field is located offshore Brazil in the northern Campos basin, approximately 120 km southeast of the city of Vitória (Fig 1). The project is a joint venture, with operator Shell holding a 50% interest and partners ONGC and Qatar Petroleum International holding 27% and 23%, respectively.
The development of BC-10 is based around a centrally located floating production, storage, and offloading (FPSO) facility; subsea wells producing through manifolds; subsea pressure-boosting systems; and a network of flowlines and risers. The development plan comprises three phases, of which the first two are complete.
Phase 1 involved the development of three fields tied back to the FPSO facility by means of subsea wells and manifolds. These fields were the Ostra, Abalone, and Argonauta-BW, and their development involved nine production wells and one gas-injection well. These fields came on stream in July 2009, with a peak production of 94,000 BOE/D. The field layout is shown in Fig. 2.
Phase 2 of the project, the tie-in of the Argonauta-ON field, came on stream in October 2013, with an expected peak production of 35,000 BOE/D. The joint-venture partners have also agreed to a third phase, which will include the installation of subsea infrastructure at the Massa and Argonauta O-South fields. Once on stream, Phase 3 is expected to have a peak production of 28,000 BOE/D.
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