ROSA: New Challenges in West Africa Deepwater Developments
Authors: Huysman Serge , Longuet Patrick , Lemaître Gilles 
Published: October 2008

Discovered in 1998, the Rosa field is located offshore Angola in the prolific Block 17, at a distance of 16 kilometers from the spread-moored Girassol FPSO. Water depth in the area is about 1,350 meters.

Sanctioned in July 2004, the Rosa Development Project proposes to tieback the Rosa wells to the Girassol FPSO. This project handles challenges never faced before in deepwater West Africa: long-length subsea production flowlines in cold environment and extensive tie-in works in simultaneous operations (SIMOPS) conditions on a live FPSO.

For processing the Rosa production on the Girassol FPSO, 5,600 tonnes of new modules, equipment and temporary steels are added to the existing installation. This paper will contribute to benchmarking such development alternative, focusing on the revamping of the FPSO topsides.

The difficulties in preparing and achieving the objectives are presented for such scale of modifications works in West Africa. The decisions that were made on the Project execution plan and on the contractual strategy for the topsides works are described with their materialization on the essential aspects of HSE, Engineering and Procurement for onshore fabrication and offshore integration in SIMOPS conditions. In particular, this paper covers the rationale and the feedback for planned shutdowns - piping tie-ins (with mandatory maintenance and inspection of existing FPSO equipment) and heavy lifts of modules - as well as the solutions implemented for the Flotel and logistical means in Angola.

Finally, the conclusions address the main lessons learnt and keys to success for the hook-up, commissioning and startup of the Rosa Project.

The significance of this paper is to share the knowledge of a major Project worked out in SIMOPS conditions, knowing that the modifications of the Girassol FPSO are the greatest ever made so far on a recent-built FPSO and lead to a worldfirst 2½-year offshore works campaign on a live FPSO.

Introduction

At concept selection stage of the Rosa Project in June 2001, new-built FPSO and new-built FPU options have been envisaged. At the time of concept selection, the economic conditions were such that the cost of a stand-alone production pole which was under consideration was too high to yield acceptable economic results. Thus these options were not carried out further.

In addition, an assumed leasing system for a FPSO or a FPU would have improved the economics without representing a major breakthrough for the Angolan economic value.

The direct subsea tieback to Girassol was the best-suited concept to reach the different economic threshold limits. This FPSO was also the ideal candidate to welcome a tieback: available areas on the topsides, recent-built plant in good condition for structural reinforcements and piping tie-ins, compatible process with Oligocene oil, extension of the production plateau and full use of an existing asset. Although it required significant challenges - innovative design criteria, coping with the overall liquid treatment capabilities in the critical years, development of existing technology for the flowlines and risers, flow assurance issues for the subsea systems, SIMOPS constraints for the hook-up phase - such project was considered feasible.