Norway’s Petroleum Safety Authority has expressed concerns over the threat Artic sea ice could pose to oil and gas installations in the Barents Sea.
As winter looms, the authority’s ice expert Arne Kvitrud said the threat was low, but nonetheless present, particularly in the Northern regions, where encroaching sea could cause significant damage to equipment, such as risers.
Kvitrud said: “In purely statistical terms, sea ice and bergs can be found south of Bear Island. But the probability is low”, says PSA’s ice expert Arne Kvitrud.
“If they’re seen today, the rule is to disconnect and move away. That hasn’t been necessary since exploration began in the far north”.
According to Kvitrud, ice could theoretically occur on the Goliat installation , for example, but the chance is so small that disconnection hasn’t been a requirement.
A bit further north, however, Johan Castberg will need a way to disconnect 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.
“The most recent drilling jobs have had to be 50km from the marginal ice zone. Should that get any closer, the rig must disconnect. No operations have been so close to the ice edge,” he added.
Icing occurs when sea spray, super-cooled rain or wet snow freezes to vessels or facilities.
In Canada, the Hibernia platform has been designed to resist the impact of sea ice and icebergs off the coast of Newfoundland.
It can withstand the impact of a one-million tonne iceberg with no damage. It can withstand contact with a six million tonne iceberg, estimated to be the largest that can drift into that water depth and only expected once in 10,000 years, with repairable damage.
The extreme Narve storm in 2006 caused heavy icing at the Melkøya gas liquefaction plant outside Hammerfest.
“Two types of icing occur. One comes from sea spray driven by wind blowing over the waves. The other is atmospheric icing, caused by rain or hoar frost”, Kvitrud explained.
Spray is the dominant source of icing on units close to the sea surface, such as supply ships or lifeboats.
On a rig or platform 20-30 metres above the surface, atmospheric icing will be the main contributor.
Super-cooled rain or other types of precipitation can eventually build up layers of ice on the structure.