Gasfield could leak for six months

It could take six months for oil engineers to drill a relief well to the leaking gasfield under the platform in the North Sea that was evacuated after gas reached dangerous levels and became highly inflammable.

A 3.7km exclusion zone for shipping and a 4.8km exclusion zone for aircraft have been imposed around the Elgin wellhead platform and Rowan Viking drilling rig 240km off Scotland's east coast.

The incident occurred on Monday during work to plug and abandon the well, which was no longer in production. Although all nearby wells have been shut down, gas continues to seep to the surface, where there is a 10km "light sheen" of condensed gas on the water.

Total, the oil company that operates the platform, said it will drill the relief well to the leaking wellhead, which could be blocked with a concrete plug similar to the technique used to stem the Deepwater Horizon spill in the Gulf of Mexico.

Another possibility is to try to block the flow of gas by injecting mud back down the existing gas pipeline leading to the wellhead. However, the company is hoping the leak will peter out over the coming days or weeks, which it said was possible given that the gasfield was already depleted when the accident happened.

"The gas is flammable but the platform power was turned off to minimise risk of ignition, but clearly there is a risk," said David Hainsworth, Total's manager for health, safety, and environment.

"We have taken away a series of risks but there is always a possibility. It's low but you never say never.

"The best-case scenario is that the gas in this area is not very productive and it dies off in the coming days and weeks.

"At the moment, there is no real evolution of the sheen on the sea but if that was to change ... then the exclusion zone may be increased."

Dr Simon Boxall, of the National Oceanography Centre in Southampton, said the gas coming to the surface was a mixture of methane, hydrogen sulphide - which are both flammable - and carbon dioxide.

"This is a fantastically advanced platform designed to pull sour gas from 5km below the seabed. They've evacuated the workforce safely, but I wouldn't want to be the one who goes in and tries to deal with this. One spark could cause an explosion."

- Independent