Total sent specialists on seven helicopter flights to Elgin over the course of last week.
Among the final preparations for the dynamic kill effort – which involved dumping heavy mud into the well itself in hopes that it will staunch the flow of gas – now in its 51st day – are the positioning of the West Phoenix drilling rig 30 meters from the Elgin complex to support the operation.
Other activities on board the platform last week included major welding of key components, deployment of communication transponders, and final testing of essential equipment, such as dynamic positioning and mist water systems, Total CEO Christophe de Margerie told reporters while attending meetings in Adelaide, Australia.
A specially manufactured diverter was also fitted to the wellhead to divert leaking gas away from the platform and crews working aboard it, Offshore Magazine reported.
Total spokesmen have been making the claim for several weeks that the level of gas leaking has been dropping since their efforts to re-plug the well, which ceased operations in February of 2011, began.
But they have until today offered no new figures or explained the methodology by which they have been gathering that data.
When the leak was detected, the gas leak figure was said to be some 200,000 cubic meters a day.
Confirmation that leak rate is falling
New reports based on 11 over flights of the platform, however indicate that the figure has dropped to around 50,000 cubic metres a day, a total spokesman told Bellona in a phone interview Monday.
Still Total was not clear about the reasons for the precipitous drop, and the figures have not yet been independently verified.
It was determined in late March that the source of the leak – which is coming from the Elgin platform, and not beneath the sea – was a gas seeping into the G-4 well’s deteriorated pipe casing from the gas containing chalk and limestone Hod formation some 4,500 – 5,000 meters beneath the seabed.
The pressure of the gas in the Hod formation was determined to be some 800 bar.
The Total spokesman said Monday that he was unable to account for the drop in the leakage rate as he had not seen the data.
But Keith Whiriskey, and advisor with Bellona, said: “I would assume the reduction of the leak rate is due to the depressurization of the Hod formation.”
“Basically it would look like the gas is running dry,” he said.
Whiriskey has noted that the 200,000 previous figure of 200,000 cubic meters a day is not historic as far as gas blowouts go.
Possible good news for pressure concerns
But that the Hod formation leak could be abating on its own could mean be good news for the dynamic kill effort.
Erlend Fjøsna, an advisor with Bellona, had earlier raised concerns that plugging the leak with mud could lead to pressure problems that the dilapidated pipe may not be able to withstand, creating larger leakage holes on the wellhead, or ultimately a new blowout.
Trygve Rinde, an expert in flow technology at Norway’s Acona Flow Technology agreed.
“The challenge of a gas blowout is that the velocities of the gases and fluids that leak are high,” Rinde told Tekniskukeblad. “This means that gas will dilute the [mud] and prevent it from circulating slowly. The operation then has to be performed faster, and pumps and pressure will experience enormous impact because of speed and friction in the well.”
Relief wells underway
The drilling of two relief wells into which leaking gas can be diverted is also underway. One is being drilled by Transocean’s semi-submersible Sedco 714, and the other by the Rowan Gorilla 5, a jack up rig.
Both are operating in about 90 meters of water and will have to hit depths of about 5,000 meters beneath the sea floor at the Hod formation, the head of Total’s crisis team, Thierry Debertrand, told Bellona in an interview early in the crisis.
According to Jake Molloy, of offshore union RMT-OILC, the rigs can work at many as 4.8 kilometers away from the Elgin platform, reducing their exposure to gas still in the air.
The relief wells, which will take some five more months to drill, have been billed as a failsafe should the dynamic kill backfire, could also serve the purpose of reducing pressure in the Hod formation, and hence the flow rate of gas from the geohazard, said Sigurd Enge, another advisor with Bellona.
He noted however, that it would be of further detriment to the climate should the relief well be required to operate in that capacity.
The gas leaking from Elgin is comprised of methane, and contains no hydrogen sulfide. But methane, one of the six greenhouse gases identified by the United Nations, is some 20 times as detrimental to the climate as carbon dioxide.
The Hod geohazard
The Hod geohazard has caused significant problems throughout the production life of the Elgin/Franklin fields, as described by Total experts in a report produced in 2005 obtained by Bellona.
“It was realized that conventionally cemented casings were unlikely to hold this gas back during the production lifecycle of the wells,” read the report.
The study resulted in improved drilling and completion procedures. However, it is clear that these procedures did not prevent gas ingress from the Hod geohazard.
The Elgin well, dating from 1997, and other older wells, may be susceptible to particular danger. It is known that other wells have shown increased annular pressure due to the Hod formation.
The Hod formation is regionally distributed, covering a wide area. It is of high pressure. Information on the Hod formation is sketchy, as the reservoir has never been commercially produced