Fifteen activists from eight countries boarded the rig Transocean Spitsbergen in the early hours of Tuesday morning, arriving in rubber ribs, scaling the rig and draping it with banners, saying "Stop Statoil's Arctic Oil Race".
"It's been a completely peaceful action and they've successfully delivered the message that they don't want this well to be drilled so close to the Arctic nature reserve Bear Island," Janice Lappegård Lahn, Greenpeace's Norway press officer, told The Local.
Lahn said that the operation had been triggered by the decision on Monday of Norway's Environment Ministry's to allow Statoil to continue with the drilling.
This, Lahn complained, contradicted a promise given on Friday that the drilling would be put on hold until Greenpeace's concerns had been examined.
Greenpeace has complained both that the drill site is too close to Bear Island, an ecologically important nesting site for birds, and that it is just 25km from the edge of the Arctic Ice Cap.
"Their own estimations state that a spill could reach Bear Island in less than a week," Lahn said. "We think this is totally irresponsible."
She added that the Norwegian Polar Institute had released data showing that the edge of the Arctic ice was just 25km from the drill site.
"The way we see it, it is a breach of the government's commitment not to allow drilling near the ice edge," she said.