Relief well 'may take six months'
It could take as long as six months to drill a relief well to stop a gas leak at an offshore platform, operators Total have said.
The company is looking at several options on how to stem the release of gas which started on Sunday.
All 238 workers were evacuated from the company's Elgin PUQ platform, about 150 miles off the coast of Aberdeen, following the discovery of the leak on Sunday.
An exclusion zone of two nautical miles (2.3 miles) has been set up around Elgin, with ships and aircraft ordered to stay away from the area. Shell has reduced its workforce on two offshore installations close to the Total platform as a precaution.
Around 85 staff have been taken off the company's Shearwater platform and the nearby Noble Hans Deul drilling rig, leaving a workforce of 117 people.
Shell also said it has brought forward plans for maintenance at Shearwater and is shutting down production in a "controlled manner".
Total E&P UK, which operates the Elgin platform, said it was taking "all possible measures" to try to identify the source and cause of the leak and to bring it under control.
The company is considering various options for dealing with the leak, one of which is drilling a relief well which could take six months.
David Hainsworth, health, safety and environment manager for Total, told the BBC that the situation poses risks.
He said: "The gas is flammable but the platform power was turned off to minimise risk of ignition but clearly there is a risk. We have taken away a series of risks but there is always a possibility. It's low but you never say never."