(Adds background about Buzzard operations, stock price)
* Bearings at gas compressor failed at the newest platform
* No spill into water
* Traders say delays on Forties loading
By Ikuko Kurahone and Jeffrey Jones
LONDON/CALGARY, April 23 (Reuters) - Output has been shut down at the North Sea Buzzard oil field, Britain's largest, following a problem with a gas compressor on the field' newest platform over the weekend, operator Nexen said on Monday.
Traders said the shutdown had been prompted by a small fire and was likely to cause delays in loading of Forties crude, which is one of the four streams used for the global dated Brent price benchmark and has been hit by repeated output problems at the field since last year.
"Saturday morning there was a bearing failure on one of the gas compressors on the fourth platform at Buzzard that resulted in smoke being emitted," Nexen spokeswoman Patti Lewis said.
"Repairs are under way and during this maintenance period, production has been halted. We expect production will ramp up over the next 24-48 hours."
She added that Nexen was investigating the cause of the problem.
The company has struggled over the past year with reliability issues at Buzzard, resulting in frequent downtime.
In February, interim Chief Executive Kevin Reinhart identified fixing Buzzard's problems as one of a handful of priorities for the company. It is looking to regain favor with investors after months of production glitches, delays and the loss of Yemen operations, which culminated in January with the exit of CEO Marvin Romanow.
Another major initiative is boosting production at the Long Lake oil sands project in Alberta closer to capacity, and Nexen last week reported some progress.
A spokesman for the UK Health and Safety Executive (HSE) said: "HSE undertook an initial investigation but decided there was no need to go offshore to investigate. Instead, HSE is awaiting the outcome of Nexen's internal investigation before deciding what action to take."
There was no oil spill into the water.
The oil field's output fell to less than half on Saturday and was shut down completely on Sunday, traders said. It normally pumps about 200,000 barrels of crude oil per day.
So far, at least one cargo loading has been delayed since the shutdown, although Nexen did not confirm that the two events were directly related.
There was no immediate word from Nexen on whether it had declared force majeure in response to the outage.
Cargo F0411 will load between May 2-4, according to trade sources. The loading dates for the cargo have been repeatedly delayed from the initial schedule to load April 14-16.
More than half of the April loading Forties cargoes have been already disrupted by production glitches before the latest shutdown.
The shutdown limited the fall in ICE Brent futures prices compared with U.S. crude futures. ICE Brent crude futures were trading 61 cents lower at ${esc.dollar}118.15 a barrel by 1631 GMT due to renewed concerns over the euro zone economy. U.S. crude fell ${esc.dollar}1.09 by the same time.
Nexen shares were up 6 Canadian cents at C${esc.dollar}19.15 on the Toronto Stock Exchange. They have fallen 17 percent in the past 12 months.
(Additional reporting by Zaida Espana; editing by Anthony Barker and Sofina Mirza-Reid)
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