World's largest FPSO assigned to Angola's first deepwater development

Jeremy Beckman
Editor, Europe

Development of Girassol will eventually involve 40 subsea wells spread out over the elongated reservoir. [19,627 bytes]
Subsurface data chart shows the overlapping channels of the Upper Oligocene B system which will be drained under the first phase of the Girassol development. [16,786 bytes]
Location of the key discoveries to date in Block 17. [23,874 bytes]
Sonangol's decision to sanction the deepwater Girassol Field development will benefit Angola's labor force, as well as a host of French contractors. The hub of this 1,350-meter water depth project will be the world's largest FPSO, designed to accommodate production over two phases from Girassol, as well as possible tiebacks from other discoveries in Angolan offshore Block 17.

The first phase, costing $2.5 billion, is projected to recover 700 million bbl of oil from the Oligocene Girassol B reservoir system, with first oil scheduled for late 2000. As expected, bundled riser towers have been chosen incorporating direct heating to combat wax and hydrate formation in flowlines caused by the cold deep sea temperatures.

Costs are being borne by operator Elf and its Block 17 contractor partners BP, Esso, Fina, Norsk Hydro, and Statoil. Their engineering methodology was outlined in a presentation last month at Elf's headquarters in Paris, led by Girassol Project Manager Antoine Serceau, Elf's Patrick Timbart, and Sonangol's Joachim David.

Following the signing of the PSA for Block 17 in 1992, four seismic surveys were commissioned over the acreage from 1993-95, and one mildly promising wildcat was drilled. But it was the Girassol-1 well in April 1996 that lit the fuse.

According to Serceau, the partners saw enough at that point to commit to a fast-track development - tailored to the circumstances. "Normally, you start with the appraisal, then the design studies, followed by the building and installation. But we decided on parallel engineering to enhance profitability." The production concept evolved as appraisal results came through. That appraisal/design process was only completed just before Sonangol's development approval in early July, hence the apparent delay in confirmation of the main hardware contracts.

Further 3D and 2D seismic was acquired after the first major discovery, followed by two successful appraisal wells in 1997. The picture that emerged was of a very large field, 18 km long and up to 10 km, deep and with a number of overlapping channels.

The upper Oligocene Girassol B system, which will be drained under the first production phase, corresponds to distal turbidites deposited from channels with NE-SW to N-S trends. The turbidites system comprises several meandering sand complex deposits of which B3 proved most productive in well tests. B2 has only been drilled in the distal level facies.

To the west of the B system is the upper Oligocene Girassol C system which has not yet been drilled, but is thought to be highly prospective. Oil reserves for the C system are estimated at 300 million bbl. Appraisal work on this system is currently in progress.

Analysis of the more recently acquired seismic has improved the team's understanding of the field and the reservoir's capacity, Serceau claimed. "That allowed us to reduce the number of development wells, which is important at these water depths."

The production system designers were also instructed to be flexible in their approach, adapting their concepts as new data came in. Various contractor groupings, mainly French, were invited to submit designs based on an FPSO with wells spread out across the field. The intention, according to Serceau, was partly for the partners to be in a position to start pre-drilling long before the FPSO was installed.

Another requirement was to devise a good use for the associated gas, instead of flaring it, as is the norm off West Africa. In the event, Girassol's gas will be reinjected to aid oil production during the first phase, but at a later date, it will probably be developed in its own right to meet Angola's domestic needs.

Bouygues Offshore and ETPM were jointly awarded the $700 million contract to supply the FPSO and offloading buoy. Although Bouygues Offshore has a good track record with concrete floaters, the partnership in this case opted for a steel hull as being more economic at a time of low oil prices. Capex for the development is estimated at $6/bbl.

The hull is being built by Hyundai Heavy Industries in Korea, while the 17,000 ton integrated deck is being assembled concurrently in Fos-sur-Mer, southern France. When complete, the deck will be skidded onto the hull at FOS prior to tow-out and installation off Angola in the second half of 2000.

Elf claims the 300-meter long, 60 meter wide FPSO will be the largest ever built, with capacity to handle:

Processing of 200,000 b/d
180,000 b/d of produced water
8 MMcm/d of injection gas at 285 bar
390,000 b/d of injection water at 150 bar
400,000 b/d of sulfate-injection water (40 mg/liter).

The FPSO will be moored by a 600-ton system composed of chains and cables. Offloading tankers will be positioned so as to avoid interference with drilling activity.

Bouygues Offshore and ETPM are also in the consortium with Stolt Comex Seaway awarded the USD410 million contract to design, engineer, build and install the associated flowlines, umbilicals and risers, in addition to managing installation of production manifolds and subsea well tie-ins.

Three 1,350-meter tall towers will house all the production, injection and gas lift risers. The riser base will be connected to the subsea production system using flowline bundles, while the tops of the bundles will be linked to the FPSO by standard flexibles. (See Offshore, May 1998, page 72 for a detailed description of this and the installation method).

Development drilling ($500 million), led by Sedco Forex using a semisubmersible built by DCN in Brest, is expected to last five years and entails 23 subsea production wells, 14 water and three gas injectors spread out across the field. Kongsberg Offshore (KOS) is supplying the subsea trees and will set up a base at Luanda to perform final assembly and subsequent maintenance operations.

Assembly of the riser towers will also be handled from Angola at ETPM's Lobito base 210 km from Girassol. Flowline bundles will be fabricated in Soyo, with installation performed in phases during 2000 and 2002. According to Serceau, the project generally will have a big impact in terms of new jobs for Angola. "Sonangol also wants to improve the technical capability of Angolans - each contract, therefore, involves training." Sonangol Aviation is responsible for helicopter flights.

Also in Block 17, Elf and partners are weighing up their Dalia and Rosa discoveries which are potentially even larger than Girassol. A pre-development concept is being studied for Dalia, Timbart said. Depending on the result of an upcoming appraisal well (and oil prices), that project could be launched before the end of 1999.

As for Rosa, two appraisal wells may be drilled next year, he claimed, but development isn't anticipated before 2003. Planning has to be fluid at this point, he explained, as further exploration successes could consign current concepts to the shredder. There are high hopes, for instance, for a Block 17 well currently in progress. In time, he added, "there could be one to five other FPSOs of Girassol's size operating in this block, or three main ones - depending on how the technology evolves."