UPDATE 1-Gas cloud seen over Total N.Sea platform after leak
* Relief well may need to be drilled to lessen leak -union
* Gas cloud visible 7 miles away -eyewitnesses
* Outer layers of pipe casing structurally compromised -union
By Oleg Vukmanovic
LONDON, March 26 (Reuters) - A gas cloud has encircled Total's Elgin Franklin platform in the North Sea after failed attempts to shut a problematic production well caused a leak, an RMT union official said, based on eyewitness accounts from workers on nearby rigs.
"People seven miles away can see a gas cloud coming from the Total rig," said Jake Molloy, the head of the section of the UK union that represents offshore oil and gas workers.
A separate relief well may need to be drilled to ease pressure and allow emergency teams to regain entry to the rig and try to fix the problem, he said, citing engineers.
"The well in question had caused Total some problems for some considerable time ... a decision was taken weeks ago to try to kill the well, but then an incident began to develop over the weekend," he said.
"Engineers have told me that it is almost certain that gas is leaking directly from the reservoir through the pipe casing," he said.
He said the only way Total can stem the leak is to drill a relief well to ease reservoir pressure.
"If gas is leaking directly from well casing below the mud line, the best recovery option will probably be to drill a relief well to intersect the problem at a point well below the leak. The relief well can then be used to kill the well," an engineer familiar with the matter said.
"This option is likely to take several months and cost a lot of money. In the meantime a lot of gas may potentially get released into the atmosphere," he added.
A shallow water-depth of 93 metres at Total's production site should make it easier to drill a relief well, compared with BP's difficulties after the 2010 Macondo oil spill in the Gulf of Mexico, which was about 1,500 metres deep.
Total, which declined to comment immediately on the cause of the leak and the need for a relief well, has not been able to stem the leak, which started on Sunday and led to the evacuation of all 238 platform personnel.
"Production has stopped," Total UK said earlier.
Molloy said the outer layers of the pipe casing have been structurally compromised, channeling gas to the surface directly from the reservoir.
"The engineer I have spoken with says that he has no idea how to go about fixing this type of problem," he said.
NOT ABLE TO SAY WHEN
Total was unable to predict when production from the platform would resume, which a spokesman said would probably not be soon.
"The gas leak at the Elgin Well Head Platform remains ongoing, and we are taking all possible measures to try to identify the source and cause of the leak and to bring it under control," Total UK said in a statement.
An aerial surveillance flight confirmed there was a sheen on the water, which was detected near the platform, and an aircraft carrying dispersant was on standby at East Midlands airport.
The appearance of a sheen, thought to be gas condensate, is a direct consequence of the gas leak and usually evaporates naturally, a Total UK spokeswoman said. Gas condensates are a mixture of light hydrocarbon liquids.
The British energy ministry said the environmental impact of gas condensate leaks is substantially lower than from oil spills.
The peak production capability for the Elgin/Franklin field is 280,000 barrels of oil equivalent per day, which includes 175,000 barrels of condensate and 15.5 million cubic metres of gas (mcm/d), according to Total.
On Monday morning, 150 non-essential personnel had been evacuated to Aberdeen and a further 69 employees had been brought to neighboring offshore installations.
Oil produced at the facility is exported via the BP-operated Forties Pipeline System to Kinneil in Scotland, and its gas flows through the SEAL pipeline to Bacton in Norfolk.
Gas flow through the Bacton SEAL terminal fell by around 10 mcm/d to 7 mcm/d early on Monday, data provided by UK energy network operator National Grid showed.
UK gas prices for day-ahead delivery surged by almost 9 percent following news of the supply cut from Elgin to 57.70 pence per therm.
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