Design, Conversion and Installation of an FPSO Vessel for Zafiro Field
Authors: Hewlett Clyde , Liles Ed , Huddleston Wayne , McCabe Chuck 
Published: October 2008

This paper describes the design, conversion and installation of a large FPSO as an integral element in the fast-track development of the Zafiro field offshore Equatorial Guinea. The FPSO, ZafiroProducer, was a key part of the critical path associated with achieving the overall goal set by Mobil Equatorial Guinea, Inc.: to begin production within 18 months of drilling the Zafiro 1 discover well. Effectively, this required the FPSO to be operational in approximately one year from the start of concept e n g i n b g. As reservoir definition was still evolving, functional specifications and classification society's requirements were used to guide the &sign. However, as an added challenge, the system required maximum flexibiity for future expansion should the Zafiro field prove to have recoverable reserves significantly greater than those recognized at project go-ahead. The FPSO is based on a 268,191 DWT tanker, with an 80,000 BOPD process plant, 40 MMSCFD gas flare capacity and storage for 1.7 MMBBL of oil. The Zafiro Producer is held on location by a 12-point spread mooring and offloads to shuttle tankers through a bow-to-bow tandem mooring system. Many interfaces with other contractors, providing flowlines, umbilicals, subsea production equipment, controls, and drilling activities were successfully managed through a true integrated team approach The project, including conversion, installation and startup, was accomplished on budget and schedule.

Introduction

The ability to accomplish a phased oilfield development on an accelerated schedule while appraisal drilling is still ongoing can offer significant economic benefits. This approach was adopted by Mobil Equatorial Guinea, Inc. (MEGI) for the Zafiro field located in the relatively deep, waters offshore Equatorial Guinea remote from existing infrastructure. The central element of the Zafiro field development was the FPSO which was required to process, store and offload oil from subsea wells in water depths ranging roughly from 430 to 875 feet. Furthermore, the FPSO was required to be operation in the field less than one year from authorization for expenditures. The project required conventional methods of project management because such a conversion would normally require approximately 18 months to complete. MEGI awarded a turnkey contract for the supply and operation of the FPSO to Oceaneering Production Systems (OPS) of Houston, Texas.

The Phase 1 Zafiro development comprises 8 subsea wells producing 40,000 BOPD through flexible flowlines to an FPSO located in 594' of water (Figure 1). The FPSO is capable of supporting a significantly larger number of subsea tie-backs as well as enhanced r e c o q equipment. Implementation of these capabilities will depend on the results of further appraisal drilling and evaluation of reservoir conditions. Phase 2 Zafiro development is presently underway. This paper describes the process by which an 80,000 BOPD, 268,191 DWT FPSO was designed, converted, installed and placed into operation to allow Mobil to achieve its goal of discovery to first oil in 18 months.

Schedule.

The most important drivers in the FPSO conversion project were schedule and cost. Many of the decisions taken were the result of schedule considerations.