* Loose barge drifts by platforms in North Sea
* BP platform evacuated, output shut down
* ConocoPhillips also shuts production
* Oil traders watching impact on cargoes (Updates throughout with barge miss, oil sector impact)
By Gwladys Fouche and Nerijus Adomaitis
OSLO, Dec 31 (Reuters) - A fierce storm in the North Sea forced oil firms to evacuate platforms and shut down production on Thursday on concerns that they could be hit by a drifting barge that had broken its anchor.
The strong winds had ripped the barge from its moorings and sent it towards BP's Valhall platform, which lies in the middle of the North Sea between Norway and Britain.
This prompted the oil and gas company to shut down output and evacuate dozens of staff on board. ConocoPhillips also stopped production and removed crew from installations in the same area.
A spokeswoman for the Rescue Coordination Centre for southern Norway told Reuters the barge eventually missed the BP platform by some two kilometres.
"The danger is over. There are no other installations between the barge and the coast of Norway," Borghild Eldoen said.
"It is now up to the owners of the barge to stop it before it reaches the coast."
A spokesman at the Rescue Coordination Centre for southern Norway earlier told Reuters that rescue boats had been trying to establish a new towing line on the barge amid difficult sea conditions, with waves of up to 15 metres in height.
BP said it was beginning the process of restarting activity on the rig, but it was too soon to say when production could resume, but that it usually took 24 hours after a complete shutdown.
ConocoPhillips declined to say when its Eldfisk and Embla fields could restart production.
The evacuations came a day after one person died and two were injured when a big wave hit a rig belonging to China Oilfield Services Ltd that had been drilling at the Troll field in the North Sea.
That rig was making its way to the Norwegian coastline on Thursday and was expected to reach land later in the day.
Close to 50 people out of 106 staff onboard, whose living quarters were damaged during the storm, had already been evacuated.
Production at the Troll gas field, operated by Statoil and Norway's largest, was not affected as the installation was a drilling rig, not a production facility, a Statoil spokesman said.
The Valhall field, operated by BP and co-owned by Hess , was producing at a rate of about 50,000 barrels per day before the shutdown.
ConocoPhillips' Embla and Eldfisk fields are also part of the Ekofisk crude oil stream, one of four North Sea crudes underpinning the global Brent oil benchmark.
The disruption could add further support to a North Sea market that has been rising due to tighter supplies of another benchmark grade, Forties, and to the wider Brent market.
North Sea traders said there was no information yet on whether Ekofisk crude cargoes had been delayed by the disruption to oil output.
"It depends how long it goes on for. It does not seem to impacting anything just yet. I don't think we'll see the impact, if there is any, until Monday," said a North Sea trading source.
The Ekofisk stream was scheduled to load about 258,000 barrels per day (bpd) in January, and the loading programme for February is expected to be issued on Monday. (Reporting by Gwladys Fouche and Nerijus Adomaitis; Additional reporting by Alex Lawler in LONDON; Editing by Toby Chopra)
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