Ice cover in Norway’s far north varies in extent with the seasons and from year to year. Due to the effects of the Gulf Stream, the southern Barents Sea is normally ice-free year round, but icebergs and sea ice can cause problems to installations if they collide.
According to PSA’s ice specialist Arne Kvitrud, ice could theoretically occur at Eni’s Goliat field, although the likelihood is so small that disconnection of the floating platform is not a requirement. Farther north, however, the future Johan Castberg facilities will need to be disconnected if ice gets too close.
“The best solution is to avoid ice hitting the platform at all. It could damage risers or other structures. So the aim is to keep well clear,” Kvitrud said.
“The most recent drilling jobs have had to be 50 km (31 mi) from the marginal ice zone. Should that get any closer, the rig must disconnect. No operations have been so close to the ice edge.”
Icing occurs when sea spray, super-cooled rain or wet snow freezes to vessels or facilities. The extreme Narve storm in 2006 caused heavy icing at the Melkøya gas liquefaction plant outside Hammerfest in northern Norway, receiving production from the offshore Snøhvit field.
Spray is the chief cause of icing on units close to the sea surface, such as supply vessels or lifeboats. On a rig or platform 20-30 m (65.6-98.4 ft) above the surface, atmospheric icing will be the main contributor, Kvitrud said.
“Super-cooled rain or other types of precipitation can eventually build up layers of ice on the structure,” he added.
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