Total is preparing to sink two relief wells to stop a gas leak at a North Sea platform in parallel with a plugging operation, a senior company executive said Friday.
Philippe Guys, managing director of the French energy giant's British exploration arm, also revealed that concerns with the well had first emerged a month ago.
The Elgin platform, situated off Aberdeen on the east coast of Scotland, is leaking a gas cloud. The last people evacuated off the installation left on Monday.
At a news conference in Aberdeen, Guys said two floating drilling rigs had been made available so they can be used to drill relief wells if required.
Total has seen around eight billion euros ($10 billion) wiped off its stock value since the 238 crew on the rig were evacuated on Sunday when the leak was spotted.
Its share price has dropped around seven percent since the start of the leak, although it rallied slightly on the French stock exchange on Friday.
"With respect to stopping the leak, we have launched two main actions which are progressing in parallel," Guys said. "The first is to carry out the well kill operation using a floating support.
"The second is to drill two relief wells. To that end we have suspended operations on two of our drilling rigs to make them available for work on the relief wells."
'Killing' the well would involve pumping so-called "heavy mud" into it at high pressure.
Guys said that when Elgin was evacuated, all the other wells on the platform "were left in a safe condition".
He said "irregular pressure" on the problem well was first observed on February 25 and an attempt to deal with it was made in the following weeks by pumping it full of mud.
"During that process on March 25 we observed a sudden pressure increase followed by escape of mud and then gas," Guys said.
He confirmed that the gas was emerging from the deck of the platform, not below the sea.
As for the cause of the leak, Guys said, "at this time there is no evidence of human error".
In a statement late Friday, Total said the situation had been stable over the last five days.
"The precise cause of the gas leak is still being investigated and efforts continue to bring it under control," it said.
While Total said it could not directly measure the gas leakage rate, its estimates are around 200,000 cubic metres per day.
It said the gas cloud was "fairly small" and prevailing winds were blowing it away from the platform and dispersing it.
A flare left burning on the platform when it was evacuated is diminishing. Left alight to burn off gas in the system, its presence has raised fears of an explosion.
"The very thin sheen of condensates (less than one micron thick) which had formed itself toward the east of the platform is currently reducing due to progressive evaporation," it added.
"For these reasons, the current impact on and risks for the environment are relatively low."
At a separate briefing in Paris, Total's director of development and production Michel Hourcard told journalists it was "reasonable" to assume that drilling relief wells could take around six months.
The environmental group Greenpeace said it would send a research vessel to the stricken platform to evaluate the situation for itself.
Greenpeace said experts on board the ship would take samples to measure air, water and soil pollution. They would also try to find the gas leak using an infrared camera and provide photos and videos of their findings.
The last major accident in the North Sea was in 1988, when the Piper Alpha oil platform operated by the US-based Occidental Petroleum exploded, killing 167 people.
Total's rival BP is still recovering from the damage to its reputation and finances caused by an explosion at its Deepwater Horizon oil rig in the Gulf of Mexico in 2010.
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