UPDATE 1-Storm throttles some Norwegian oil, gas output

* High waves force Satoil to shut down three platforms

* Power failure knocks out Kollsnes gas processing platform

* Storm “Berit” packing winds up to 25 metres per second (Adds Statoil, Gassco comments, weather forecast)

OSLO, Nov 25 (Reuters) - Norway’s Statoil said it was shutting down production at its floating Njord, Heidrun and Aasgard platforms in the Norwegian Sea as Atlantic storm Berit roared off central Norway and a power dip knocked out some gas processing operations.

“We have decided to shut down production at three of our installations in the Norwegian Sea,” said Statoil spokesman Ola Anders Skauby. “This is done as a precautionary measure.”

The three platforms have a production capacity in excess of 130,000 barrels of oil per day, according to the Norwegian Petroleum Directorate.

Kjell Varlo Larsen, a spokesman for North Sea infrastructure operator Gassco, said the onshore Kollsnes gas processing plant near Bergen briefly lost power soon after 1500 GMT and shut down automatically before restarting with partial effect.

“There has been a power dip on the grid system,” he said, adding that he did not know if it stemmed from the extreme weather.

Meteorologists were reporting huge waves and winds of 20 metres per second between Bergen and Trondheim on the central Norwegian coast, with forecasts calling for gusts to reach 25 metres per second on Friday night.

Skauby said oil and gas installations that float -- like Njord, Heidrum and Aasgard -- were more exposed to wave action than those with legs on the seabed.

“We are not evacuating any of our platforms,” he said. “We have just removed some of the non-critical personnel.”

The onshore Kollsnes plant processes up to 143 million cubic metres of gas per day from the vast Troll field in the northern North Sea as well as the nearby Kvitebjoern and Visund fields, most of it bound for European markets by pipeline.

“They are now in a restart mode, with enough power to restart one compressor, and will start delivering some gas during the evening and increasing during the evening,” Larsen said. “But I cannot predict beyond that.”

Kollsnes has five compressors, he said. In a note to the Nordic power bourse, Gassco reported at 1521 GMT that the processing plant was consuming 86 MW of its maximum 270 MW.

The Troll A platform was expected to produce some 28.7 billion cubic metres of gas in 2011.

Statoil’s Skauby said the platform shutdowns were to be done in steps lasting into Friday evening. He said they would not last long but declined to say when production would resume.

The semi-submersible Njord platform was expected to produce some 13,000 barrels of oil per day in 2011 as well as 2 billion cubic metres of gas for the year, according to the Norwegian Petroleum Directorate.

Heidrun, a floating concrete platform, was to turn out 52,000 barrels of oil per day and a total for the year of 760 million cubic metres of gas.

The floating production and storage vessel Aasgard was to have daily oil output of 70,000 barrels per day in addition to a 2011 total of 11.6 billion cubic metres of gas. (Additional reporting by Victoria Klesty; Editing by Anthony Barker)