SEMISUBMERSIBLE DESIGN Åsgard, Troll awards confirm GVA's eminence in floating production

Nick Terdre
Contributing Editor

The turn of the year proved a memorable one for GVA Consultants, as it clinched two leading contracts for the provision of floating production platforms in the North Sea. These are Statoil's Åsgard B platform, for which the main contract has been won by Kverner, and Norsk Hydro's Troll C platform, on which the lead contractor is Umoe Haugesund.

The overall EPC contracts are worth NKr 6.6 billion and NKr 3.9 billion. In both cases GVA Consultants, which is providing the basic platform design, will earn some NKr 30-40 million.

The Gothenburg-based company has now won the last three contracts for newbuild semisubmersible production platforms in the North Sea, points out managing director Hugo Heyman. The other one is the Visund platform, another Norsk Hydro contract won by Umoe and GVA in partnership.

Both Åsgard B and Troll C will make notable additions to GVA Consultants' reference list. According to Statoil, the development contract for Åsgard B is the most valuable in the history of Norway's oil and gas industry. With a hull weighing some 17,000 tons, a topsides of some 28,000 tons, and pontoon dimensions of 102 x 96 meters, the Åsgard B platform will be the biggest steel-hulled production floater ever built.

The platform, which will be able to handle up to 40 risers, will have the capacity to process a massive 38 MMcm/d of gas and 94,000 b/d of condensate, and to reinject 11 MMcm/d of gas.

Designated Kverner GVA 70, the basic design has been developed by GVA, with some modifications proposed by Kverner. These relate primarily to utilization of the deck space - the deck structure has been minimized to allow most of the equipment to be installed directly on it in the form of modular packages.

Ring pontoon

Maintaining the flexibility to accommodate additional demands is one important reason why the Kverner GVA team won the contract, Heyman maintains. "We offered a simple structure with a fair amount of robustness, and with a very high deck load capacity margin, so that we can handle future tie-ins," he says. "We are now looking at making modifications to cope with an extra 5,000 tons of topsides capacity. We can easily incorporate this without changing the overall geometry."

The 70 in the design name refers to the 70,000-ton displacement envisaged for the platform at operational draught. The effect of additional requirements has been to raise this figure to nearer 80,000 tons.

Troll C

The Troll C platform, which is little more than half the size of Åsgard B, is to be built to the Umoe GVA 8000 design, the same as that used for the Visund rig. The main difference is that Troll C does not require drilling facilities. It will have an oil processing capacity of some 125,000 b/d to handle the output from 32 wells in six clusters which will be tied back to it. The topsides will weigh some 19,000 tons and the four-column hull about 9,000 tons. Again, the design incorporates the flexibility to accommodate future tie-backs.

"We will benefit considerably from the Visund experience," says Heyman. "We will copy as much from Visund as possible." Advantages will accrue, not only from using the same basic design, but from the two companies' familiarity with each other, and a shared philosophy.

"Over the last couple of years we've developed a good relationship with Umoe," Heyman explains. "They are limited in size and aggressive, and have the same approach to business as we have - don't overdo things, keep them simple."

For more information contact Hugo Heyman, GVA Consultants: telephone +46 31 106 760 or fax +46 31 135 692.