Decommissioning is the newest big market opportunity to develop in the North Sea.

After 25 years of production, many forecasts originally predicted, the North Sea sector would see the removal of most fixed platforms as they reached their sell-by date.
The forecasts were wrong - production-enhancement projects are coming forward all the time - but that hasn't stopped the development of decommissioning solutions for the start of the endgame.
Many of the systems under development are spectacularly huge. The thinking is that low-cost solutions using single-lift techniques to pull off topsides from a jacket in one go will minimize the time spent operating offshore and therefore reduce overall project costs.
Phillips Petroleum and TotalFinaElf in Norway have large decommissioning projects in the future - Ekofisk and the Frigg area. Many concepts, predominately Norwegian and Dutch in origin, have evolved to supply decommissioning solutions. The Marine Sea Lifter concept from SeaMetric of Norway is a new entrant to this market that shares giant dimensions with its competitors.
Phillips has invited companies to tender for the Ekofisk decommissioning work. Phillips and its partners are expected to use the competition as a technology development process to encourage options for a series of decommissioning projects. Other operators will be watching closely to learn of alternatives to the heavy crane barges available from Heerema and Saipem.
Most of the focus is on single-lift techniques. Eight companies with single-lift concepts are lining up to receive the support of a group of oil companies and eventually compete for the first Ekofisk removal jobs in 2003. Phillips, with experience of refloating the UK Maureen platform under its belt, is looking to award a contract for removing its redundant compression platforms Norpipe 36/22 A and 37/4 A in the UK North Sea to a company with single-lift technology this fall.
"Some are just concepts, but just one of them, the Versatruss, is physically in existence," said Rolf Olavesen, sales and marketing manager for Stavanger, Norway-based SeaMetric.
But, he added, Versatruss is reliant on a fairly calm sea state, with a 7- to 16-ft (2- to 5-m) significant wave height maximum. This is a big issue in the North Sea, where sea conditions and wave heights will have to be factored into lift designs.
Other solutions claim to offer a wider operating envelope for higher sea states. Apart from the sea state for these operations, single-lift is important in reducing removal cost.
"If we can do a single-lift, we can reduce costs by between 30% and 40%," Olavesen said.
SeaMetric's solution, which first appeared at the Houston Offshore Technology Conference in May, is based around two barges, each fitted with three to six lift arms. Each barge measures 390 ft by 140 ft by 29 ft (120 m by 43 m by 9 m). The lift arms would be inserted below the topsides. A combination of buoyancy and ballast tanks activated on the barges would provide the lifting force. Once topsides are severed from a supporting jacket, a third heavy transport barge would be maneuvered into position below the topsides to remove them.
Each single arm can hoist between 200 and 2,000 tonnes, giving the whole system a capacity of up to 20,000 tonnes.
SeaMetric claims it can reduce preparation time for a lift 50% to 70% and reduce emissions by up to 80%. Total marine operations costs can be reduced 30% to 50%, and marine operations cut by half, based on comparisons with a traditional heavy-lift barge working with medium-size topsides.
Other potential solutions are coming out of Norway too. Oslo-based MPU Enterprises is working on the MPU Heavy Lifter, a semisubmersible concrete rig with a 30,000-tonne single-lift capacity.
Stavanger-based Marine Shuttle Operations has the Offshore Shuttle, featuring large-diameter steel tubular sections around a semisubmersible hull made from unconventionally large steel tubular sections with through nodes. This concept can remove platform jackets of up to 12,000 tonnes (18,000 tonnes with modifications) and topsides of up to 22,000 tonnes.
Versatruss America's solution consists of two barges. Its lift capacity depends on the barges used, thus offering flexibility. This is the only concept that has seen actual use in the Gulf of Mexico and Venezuela.
GM Lift is another single-lift concept for up to 25,0000 tonnes. It consists of a rebuilt semisubmersible platform with a new section in front, representing the hull carrying the topside to be removed.
The Dutch Pieter Schelte concept from Excalibur Engineering is a single-lift catamaran constructed with two sister tankers connected from midship to the rear. This is the largest concept that would allow removal of topsides up to 48,000 tonnes and jacket up to 25,000 tonnes.
Master Marine's MasterMind is a multipurpose "forklift"-shaped semisubmersible vessel. Lifting capacities are 14,000 tonnes for topsides and 20,000 tonnes for jackets.
France's Doris Engineering is offering Archipose 2000, a semisubmersible rig with a 20,000-tonne capacity.

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