Safety vessel Fennica’s arrival in the Chukchi Sea, after activists attempts to delay it, clears way for company to start drilling deep enough to hit oil

Shell is set to restart its controversial hunt for Arctic oil, three years after the company’s last ill-fated venture north.

The Polar Pioneer rig began drilling on 30 July, but US safety standards have prevented the company from sinking a well deep enough to hit oil until a key safety vessel, an icebreaker called the Fennica, was in the Chukchi Sea.

But Shell said on Tuesday that the vessel was now in the area and it had informed the US Bureau of Safety and Environmental Enforcement that it was ready to go for oil.

Ann Pickard: the little-known executive leading Shell's gamble on Arctic oil Read more

A spokeswoman for the company said: “Fennica is in the Chukchi Sea, drilling continues, and we have requested the permit to drill deeper in this exploration well.”

The Fennica carries a capping stack, a device that can be lowered on to a leaking oil well to control a blowout. Arctic operating standards, formed in the wake of the Deepwater Horizon disaster, require this device to be available within 24 hours. But while Shell’s fleet was preparing to enter the Chukchi Sea in July, a metre-long gash was found in the hull of the Fennica, forcing it to return to Portland for repairs.

Shell Arctic boss, Ann Pickard, called the response to the Fennica accident “a perfect example of operating exceptionally well”. A company spokeswoman added: “We will take the time we need to do it safely.”

A second rig, the Noble Discoverer, is ready to begin drilling. But federal regulations governing noise disturbance to local walrus populations mean both rigs cannot drill at the same time. The second rig is also required nearby in order to sink an emergency relief well to divert pressure from a blowout – a standard Shell has lobbied hard to water down.

As shallow drilling began on 30 July, the Fennica was leaving dry dock in Portland after a standoff with Greenpeace protesters who rappelled from a bridge and delayed the ship from making its way to the Arctic.

The US Geological Society has estimated that the Arctic may hold 90bn barrels of oil, 13% of the world’s undiscovered reserves. But until now, few companies have explored the area extensively. Shell has spent $7bn (£4.5bn) to date on its bid to prove these resources exist.

The company’s Arctic programme resumes after a three-year hiatus caused by a disastrous year in 2012, which ended with one of its rigs washed ashore on a beach in Alaska. Critics question Shell’s assertions that it is capable of operating safely in the treacherous conditions in the Arctic.

The new cold war: drilling for oil and gas in the Arctic Read more

Charlie Kronick, senior climate advisor to Greenpeace UK, said: “Shell’s catastrophic record since 2012, as well as their mishap-plagued progress to Alaska this year, show just how unprepared they are for the harsh conditions of the Arctic. The company is patently unwilling to call time on this wasteful and potentially catastrophic project. It’s now up to the regulators and investors to do so.”

Concerns have also been raised over Shell’s ability to clean up a spill in an area covered by sea ice for much of the year.

Pat Pourchot, who worked closely on Shell’s programme as the US Department of Interior’s special assistant for Alaska affairs from 2009 until February this year, told the Guardian that if a large spill did occur: “It’s really tough to talk about effective clean up. I don’t think anybody should have illusions. Clean up will be extremely modest.”

Shell has said it has mitigated the risks of a large spill as much as possible.