Meanwhile, Bellona President Frederic Hauge remained concerned about the leak’s origins, which have only been established by Total – the rig’s owner – as coming from  “a (gas) well that was plugged one year ago, and from a rock formation in about 4,000 meters depth,” Reuters reported.

Hauge questioned whether it was coming from the reservoir itself or from pocket gas above the reservoir. Other important considerations are whether the gas is coming through pipe casing or through the geology surrounding the well itself.

Bellona expects more information will be revealed by the remote submarine inspection that Total is today carrying out.

Should the gas be flowing from the reservoir, Hauge said staunching the flow could be a long time operation. If, however it is coming from a gas pocket, it could well bleed itself out.

As the leak continues into its fifth day on the North Sea platform, both good and bad case scenarios present themselves.

“It’s of course bad that the leak continues. Any leak going on like this is a very serious issue,” said Hauge. “ It is positive that it seems like the leak has not increased its flow rate dramatically in the last days.  That indicates that the leak is coming up through the well  [pipes] and not through the geology which would be a worse scenario,” he said, adding that, “If the leak is inside the pipe casing it could enable Total to use mud and liquids to stop the leak.”

If gas is coming up through the well, said Hauge, it is likely that the gas is leaking through the plug used a year ago to close it.

“This is serious because there is a chance that the pressure will dig a wider pathway on its route to the surface,” said Hauge.

In this case, said Hauge, the best-case scenario would be that sand and other debris plug the leak.  A worse case scenario would be that the gas’s pressure would punch a pathway through to the sea floor allowing for a total release.

An absolute worst-case scenario would be that this leak is connected to what’s called the Franklin West reservoir, which contains more than 15 billion cubic meters of gas at pressures of more than 1100 bars.

Gas could be coming from a pocket in pipes

Today New Scientist reported the leaking gas does not contain hydrogen sulfide.  This is good news as it suggests that the gas lead could be emerging from a gas pocket in the pipes above the reservoir. The absence of hydrogen sulfide also implies less ecological damage.

“We now know the gas is not toxic,” says a spokeswoman for Total, the platform’s owners, although it is not clear how the company has come to that conclusion, said New Scientist.

Bellona suggests – based on the revelations by Total of the depth of the leak – that the gas is escaping from a gas pocket in a so-called Hod Formation within the well pipe located about 4,000 meters beneath the seabed.

The Hod Formation is not expected to contain any hydrogen sulfide, suggesting that the source of the leak is within the pipe structure rather than from the reservoir itself

Total itself produced a report in 2005 warning of the risks of leakage from the Hod formation due to high pressure and the poor condition of the well casings.

In the 2005 report said of the  Elgin/Franklin/Shearwater area in the North Sea: “It was realized that conventionally cemented casings was unlikely to hold this gas back during the production lifecycle of the wells.”

“If the leak’s origin is a gas pocket, we would be very happy to exclude a worst-case scenario,” said Hauge. “But if the situation remains unclear, and could still develop into a bad case scenario even if we hope for the best.”

The flare

Total officials have claimed for the past day since the flare was revealed that conditions at the rig remain completely safe as the gas cloud emanating from what the company is calling a surface leak at the platform remains upwind of the flare.

One total spokesman told Reuters the flare and the escaping gas cloud, which is 90 meters upwind of the flare are on separate parts of the Elgin platform.

“The flare is still burning but is not posing a risk. The leak is on the wellhead platform and the flare is on the Processing, Utilities and Quarters platform. There is a gap of 90 metres between the two,” said the spokesman, who remained unidentified.

Hauge, however, noted that the prevailing winds, which are coming from the west, have kept the flare from developing into an explosion.

“Should the winds die down or change course, we fear it could result in a major disaster,” he said. This, he said, would likely include damage to other rigs in the area. Various estimates have put a €10 billion price tag on a possible explosion.

The leak at the Elgin platform, some 240 kilometers east of Aberdeen, Scotland, was discovered on Sunday as water beneath the rig appeared to boil, according to eyewitnesses cited in British media. The rig was totally downmanned by Monday.

David Hainsworth, a health, safety and environment manager at Totalhad yesterday dismissed the possibility of a blast due to the ongoing flare, saying it would most likely burn itself out. The British government said the flame had to remain burning to prevent excess gas pressure from building up, the BBC said.

On Tuesday morning, the spokesman for Total who spoke with Reuters that, absent the flare extinguishing of its own accord, the company had to consider different alternatives to extinguish the flare itself.

Hainsworth could not say how long it would take to extinguish the flame, and whether that would be “an hour, or 24 hours or two days” – or even longer.

Why did the flame remain lit?

But questions still linger as to why the flame was left alight after the evacuation. The British government said the flame was still alight as part of the safety system triggered during the evacuation to burn off excess gas.

A statement released late Wednesday by Total corroborated this.

“The flare is still lit because when the platform is shut down and de-pressurised in an emergency, it cannot be fully purged as done in a controlled shutdown,” Total said in its Wednesday statement.

“Some liquids do remain in the system and these liquids are now evaporating.  As these liquids evaporate the flow of hydrocarbons to the flare will exhaust itself and the flare should burn out,” said the statement.

Total explained that the flare is “an integral part of the platform’s safety system…  used to safely evacuate all the gas from the platform” during an emergency. 

“When the emergency de-pressurization is initiated, all hydrocarbons feeds are closed and valves are opened on installations vessels to de-pressurize gas to the flare,” the statement continued. “These valves remain open as they are designed to in such circumstances.”

Source of the gas remains in question

Even with Total’s encouraging revelations about the depth of the leak and the announcement – however unsupported – that the leaking gas is not toxic, it is apparent that Total still has much explaining to do.

“We still don’t even know what well we are dealing with,” said Bellona advisor Keith Whiriskey. “Until now we had been assuming it was coming from a West Franklin reservoir, but it may be coming from an adjacent Eglin reservoir, or a shallower pocket of gas. It’s clear that Total needs to provide more information on this.”

The possible lack of hydrogen sulfide in the gas may indicate that the source of the leak is not a primary production reservoir, but a smaller and shallower pocket of gas,”

This could suggest two things, said Whiriskey: that the current gas leak is coming from a pocket that was trapped when the well was sealed a year ago with drill mud, or – a more dire circumstance – from a well rupture around the old plug.  Further evidence that the gas may be bubbling to the surface from a pipe casing rupture  – known as an annular blow – and not seeping up through the geology surrounding but through the well itself as there has been no increase in the flow. Such a rupture, he said, would have been caused by liner deformation, which is potential sheering in the pipe.

Whiriskey also said has been indicated that the gas pocket  may be located in a chalk zone, pointing toward a shallow gas leak, a situation wherein shallow gas is escaping into the piping, and either rises to the surface between a ruptured outer casing and an intact inner casing, or via an annular blow.

Should this be the case, said Whiriskey, this could mean a less critical situation than a leak from the production reservoir – depending on the quantity of pocket gas, which may be small.

Total itself still does not know how much gas has escaped, how fast it is escaping or how much is in the source reservoir. A surveillance plane overflew the area at 8 am UK time today, and confirmed that there is a sheen of condensed gas and mud on the surface of the sea, with a volume of roughly 30 cubic metres, New Scientist reported.