Authorities are expected to grant French oil company Total permission in the next few days to kill its leaking Elgin well in the North Sea, industry sources said on Sunday.
Total wants to launch two processes in parallel to stop the gas leak from the well - which is emitting potentially explosive gas - but cannot proceed without a green light from Britain's Health and Safety Executive (HSE).
If Total passes a risk assessment by the HSE it can then proceed with stopping the leak.
Authorisation for both options should land early next week, perhaps on Monday, one of the sources said.
Commenting on the risk assessment, an HSE spokesman said: That process is ongoing. I cannot comment on timelines.
In the first process Total will inject drilling mud to kill the leaking well, although this remains a risky option as human intervention on the platform would be necessary.
The second process involves digging two relief wells, which could take six months and cost up to $3 billion.
Total CEO Christophe De Margerie said on Saturday a flare near the drilling platform went out without intervention, reducing the threat of explosion at a massive gas leak.
The flare had been lit as part of Total's response to a gas leak at the platform off Scotland's east coast, in order to relieve pressure in the well. Located about 100 metres away from the rig, the flare raised fears of a massive explosion were it to ignite the natural gas that has been leaking for a week below the platform. While Total had dismissed the risk of a blast, one engineering consultant warned that Elgin could become an explosion waiting to happen. The leak is spewing an estimated 200,000 cubic metres of natural gas into the air per day, forming a highly explosive gas cloud around the platform.
It began after pressure rose in a well that had earlier been capped.
Total evacuated its 238 platform workers, and set up a two-mile exclusion zone for safety reasons, with fire-fighting ships on standby.
A senior union official said on Friday that Total had repeatedly assured workers a leak was impossible until just hours before evacuating them.
(Editing by Alexandria Sage and Karolina Tagaris)