A 3 year research and development program on floating production systems (FPS), instigated by the Royal Norwegian Council for Scientific and Industrial Research (NTNF), has refined and qualified technologies for North Sea and arctic conditions.
The FPS 2000 program, which cost 58 million kroner ($10 million), concentrated mainly on mooring systems and pipeline technology, along with new system concepts and cost reduction measures.
More than 30 projects have been completed within the scheme. The anchoring and positioning project concentrates on developing methods for simulating behavior of mooring systems for large volume structures in deep water. It also seeks ways to determine efficiency of dynamic positioning thrusters under extreme conditions.
Carried out by Marintek of Trondheim, the project is claimed to have developed a fast, simple, and reliable method of designing mooring lines. Designers usually take a quasistatic approach to catenary mooring systems. This ignores sources of dynamic tensions that occur in deep water.
Another approach, dynamic analysis using nonlinear finite element analysis programs, was time consuming, limiting the number of alternatives that could be considered in a practical design.
The Marintek solution uses two frequency domain methods for estimating dynamic tension. Much faster than the normal finite element approach, it has been applied in the Mimosa-2 package.
A project carried out by EB Global Engineering AS combined surface-completed wellheads, rigid risers, and a turret-moored production and storage vessel into a new development concept. A 1:100 dynamic model illustrated relative motions of the rigid production deck, turret, and vessel.
The concept awaits detailed design and optimization of components. ABB says that, depending on the number of wells and complexity of topside process equipment, significant cost reductions should be possible compared with conventional technology.
SUBSEA PREFERENCE
While floating production technology looks increasingly attractive in theoretical terms, oil companies still seem reluctant to choose floaters in preference to subsea completion systems. Of 57 prospective developments identified on the U.K. continental shelf, 25 are subsea developments vs. two floaters.
Prospects are not all bad for floating technology applications, however.
NTNF believes many of Norway's prospective developments are suitable for development via FPS technology (see chart).
And in the U.K. North Sea, Gryphon oil field, operated by Kerr-McGee Oil (U.K.) plc, looks set to be a showdown between floating and subsea production.
The most likely option is said to be the production ship Tentech 850, which is near completion at the Astano yard in Spain.
The Gryphon group is looking to buy the vessel so it will have something to sell or redeploy when the field is depleted.
With a vessel price of $250 million, the capital outlay for the project is now thought to be 260-270 million ($500-520 million), a considerable reduction from the 400 million ($768 million) estimated at the outset of the project.
AMERADA'S EXPERIENCE
Amerada Hess is using a floater, the converted AH001 semisubmersible, to develop Ivanhoe and Rob Roy fields in the U.K. North Sea.
It opted for a floating production system to contain development costs during a period of low oil prices-1986.
Amerada thus cut outlays for the two fields to 340 million from 480 million (to $650 million from $920 million). It won a Queen's Award for technology because of its innovative approach.
Sam Laidlaw, Amerada managing director, thinks prospects for the technology are bright.
"It is possible that in 10 years or less there will be fleets of floating production vessels crisscrossing the North Sea, servicing many dozens of small oil accumulations," he recently told a London conference.
"For small fields this is our vision of the future."
A concerted floating production program would involve developing North Sea fields in series, with two or three operators jointly providing collateral for bank loans to finance a suitable fleet.
Then developing fields back to back would simply require chartering of the production vessels.
Laidlaw cited Amerada's Angus field, which with estimated reserves of less than 10 million bbl was deemed uneconomic when it was discovered in 1983.
"This demonstrates that small can be beautiful. With its modest recoverable reserves, an expected field life of less than 2 years, and an oil production rate of more than 25,000 b/d being achieved through a monohull vessel, Angus is very much the shape of the future in the North Sea."
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