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Tyrihans submerged

April 24, 2007, 09:00 CEST

The seabed of the Trondheim Fjord in Norway will be used as a temporary storage place when the Tyrihans project and contractor Subsea 7 test out a new method for installing subsea templates.

Local residents around the Trondheim Fjord have been witness to an entirely unique operation this weekend. The large Uglen crane vessel will be shuttling between the Port of Trondheim and the Åsen Fjord with the Tyrihans project's subsea templates attached to her crane.

The Uglen crane vessel hoists up the first subsea template from a barge at the Port of Trondheim. Each template covers an area of 650 square metres. (Photo: Scanpix/Geir Otto Johansen).

When Uglen arrives at the Åsen Fjord, she lowers the templates to a water depth of 55 metres. Normally an operation only personnel at sea witness, this is the first time part of an entire subsea development can be studies from shore.

The Tyrihans templates will only lie in the Åsen fjord for a few weeks. Subsea 7's Botnica construction support vessel will raise each template one by one through a midships opening, called the moonpool. The templates, which will be suspended under the hull, will be towed to the Tyrihans field in the Halten Bank area of the Norwegian Sea, for final installation.

Uglen, ready to temporarily place the Tyrihans templates 55 metres below the surface of the Åsen Fjord. (Photo: Scanpix/Geir Otto Johansen).

The lifts in the Åsen Fjord make template installation both cheaper and safer, explains Ståle Gjersvold, Statoil's Tyrihans project manager.

"We would have to have used the world's largest installation vessel if we decided to install the templates from a barge at the field," he says.

"These vessels are both difficult to get hold of and expensive."

Uglen is both lighter and more easily available, but the vessel can only operate in calmer waters near shore.

Statoil and partners have invested NOK 14.5 billion in Tyrihans, which is being developed with five templates tied back to the Statoil-operated Kristin field. Statoil's share ownership in Tyrihans is 46.8%. The other partners are Total (26.51%), Norsk Hydro (12%), Eni (7.9%) and ExxonMobil (6.75%).