Zafiro Field Subsea Flowlines and Umbilicals Designed, Manufactured, and Installed in Record Time
Authors: Nooteboom U. , Menieri P. 
Published: October 2008

In August 1996, the first offshore oil field in Equatorial Guinea, West Africa, came on stream. First production was achieved within a record 18 months after discovery. Within that time frame the subsea flowline system was designed and 38 km of flexible flowline was manufactured and installed in water depths ranging from 140 to 270 m. The use of flexible flowlines accommodated a complex routing in a congested field within close proximity of wells and drilling rigs. Flexible flowlines also provided the necessary flexibility in project scheduling and allowed system changes late in the project as more reservoir information became available. The sloping seabed presented some unique requirements for the tie-in sleds and posed several installation challenges. This project also marks the first time that flexible well tie-in jumpers were installed successfully from a dynamically position construction vessel.

1. Field Description and Background

The Zafiro field (Spanish for sapphire) is located in block B, 40 miles west of Bioko Island offshore Equatorial Guinea, West Africa (see area map in Figure 1). The field is in water depths ranging from 140 m to 270 m. Mobil Oil is the majority share holder, owning 75% of the lease, with UMC owning the remaining 25%. The field was discovered in January 1995 with the Zafiro 1 well, after drilling a previous dry hole. Three more appraisal wells were drilled, confirming the presence of a commercial quantity of high quality oil. Based on favorable economics, the decision was made in August 1995 to develop the field. Mobil Equatorial Guinea Inc. (MEGI) was formed, and an ambitious target date for first production of August 1, 1996 was set, a mere 18 months after discovery. Considering the total lack of infrastructure, both offshore and onshore, and the fast track nature of the project, a development plan was put forward based on eight subsea wells producing into a permanently moored Floating Production Storage and Offloading (FPSO) tanker. This would maximize portability, allow the production facilities to be completely outfitted before being brought to the site, and minimize local construction and offshore hookup. In order to meet the fast track schedule, it would be necessary to utilize existing technology and solutions to the maximum extent possible

2. Overall System Description

After the discovery, three appraisal wells, Opalo 1, Zafiro 2, and Zafiro 3, proved the field to be commercially viable. These wells were drilled and configured to later be completed as development wells should it be decided to fully develop the field. The development plan called for four additional wells to be drilled, designated as Opalo 2, Zafiro 4, Zafiro 5, and Zafiro 6.

While the appraisal wells were being drilled, field development engineering progressed. It was decided to drill the remaining four wells as satellites, and produce each well through an individual 6-inch flowline and riser to the FPSO. This would avoid the cost and time associated with templates or manifolds and keep the system as simple as possible. Given the possibility of paraffin in the produced fluid stream, an arrangement was selected so the flowlines could be periodically pigged.