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.
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