Improvements in Design of Converted FPSOs Regarding 20 Years Operation Without Docking

Abstract

Abstract This paper presents improvements on basic and engineering design of four converted VLCCs that will be operated as FPSOs in Brazil's Campos Basin. Conbersion of these VLCCs is under way, worked on by contractors around the world, the first of them being scheduled to start operations by the middle of 1997. Project economics demand that the units be operated during the next 20 years without docking. PETROBRAS offshore operations and maintenance expertise were applied to achieve this goal, meeting unique FPSO operating conditions. Experience and data gathered by project team members and technical staff are now being incorporated into next generation units, which are at present moment in Design Basis phase. Although these improvements will only show their effectiveness after units come into steady operation, we are confident that major achievements in safety and economics have been made successfully. Introduction The discovery of Marlim and Albacora, giant deep water fields in Campos Basin, offshore Rio de Janeiro state, will allow PETROBRAS, a remarkable increase in national oil production. On the other hand, due to the difficulties related to deep water production, distance from the shore and from existing facilities, the start of commercial production of hydrocarbons from those fields as quickly as possible, in the most economical way, within good reservoir exploitation techniques and preserving the environment is also an enormous challenge to the Company. The traditional solution adopted by PETROBRAS for offshore production, the utilization of semi-submersible platforms (SS) as floating production units (FPS) and the pumping of oil and dispatching of gas by pipelines or the pumping of oil through monobuoy, was used in pre-pilot and pilot units in Marlim field (P-XI11 and P-XX), Stationary Production Unit (UEP) N.l in Marlim (P-XVIII), and in Albacora field (P-XXIV and P-XXV). Other units of the same type are planned, such as UEPs 2 and 3 in Marlim (P-XIX and P-XXVI). However, in order to complete development of the fields, it would be necessary to expand the pipeline network, by the construction of new pipelines, or by the installation of new monobuoys, considered to be the "weak links" in the system, as the existing pipelines could not stand the increased flow. The technical and economical viability study shows as the best option, the installation of FPSOs. Due to the estimated field life of 20 years, and considering the complexity of the pull-in and pull-out operations, the study indicates the permanency of the units on location until the end of the life of the field, without docking. The definition of the necessary storage capacity of the FPSOs took into consideration the estimated oil flows forecast for the fields, the availability of the tanker fleet to be used as relief vessels and, aiming to reduce operational costs, a lower frequency of offloading operations. With PETROBRAS having some VLCCs available, the option of converting them into FPSOs came into consideration.