The publication of the studies’ findings coincide with a Total announcement that they will this week begin the process of a dynamic kill from the Elgin platform itself – which involves pumping heavy mud into the well to staunch the leak. The company is also drilling two relief wells.

Chemical analysis of fish samples collected by Scottish government research group Marine Scotland just outside the two-mile exclusion zone around the Elgin platform found no residues of oil or gas, the BBC reported.

“All of the chemical and sensory testing work carried out by Marine Scotland on the effects on the marine environment of the leak has now concluded that there is no direct impact,” Scottish Environment Secretary Richard Lochhead said in a statement to media.

Water, sediment and fish tasting analysis published last month had already indicated that none of the samples contained hydrocarbon contamination. The Scottish government said the test results were reassuring, but that environmental monitoring would continue, said the BBC.

Stopping the leak in fragile conditions

The two relief well Total are drilling will eventually be used to redirect the flow of gas should the dynamic kill fail.

The company has said that the amount of gas being released by the platform leak has been diminishing since the end of March, but has not provide no new data or methodology on how it reached that conclusion.

Bellona telephoned Total headquarters in France to establish what the new claimed lower leak rate is, but telephone messages were not returned by publicaton of this article.

The leak figure reported by the company’s crisis team head, Thierry Debertrand, in an interview with Bellona on March 30 was 200,000 cubic meters a day.

“The environmental results are encouraging, but we would still like more specific information from Total on its assessment of the leak rate,” said Keith Whirskey, an advisor with Bellona. “We’d like to know how this is being measured, how fast the flow rate is decreasing, an what the current rate is.”

Whirisky noted that 200,000 cubic meters a day is not particularly large, so theres seems to be little to hide. He added, however, that Bellona would like to hear accurate figures on the imppact of the methane entering the atmosphere thanks to the leak. Of the six major greenhouse gasses identified by the Kyoto Protocol, methane is estimated to have 20 time the deterimental effect to the climate that carbon dioxide does.

During the course of the leak – which began on March 25  and led to the evacuation of all 238 workers aboard the platform –  Total have issued a number of statements about its characteristics without saying how they arrived at their conclusions.

The source of the leak

It was determined that the gas is ingessing into Elgin’s G-4 well from the so-called Hod formation, a natural gas-bearing limestone and chalk formation located 4,500 meters below the seabed.

The Hod formation is regionally distributed, covering a wide area. It is of high pressure – 800 bars according to the Total spokesman. Information on the Hod formation is sketchy, as the reservoir has never been commercially produced.

However it is know that the gas it contains is clean, meaning that it does not contain hydrogen sulfide. This will result in fewer detrimental environmental impacts.

The Elgin G-4 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.

Weighing the risks of the dynamic kill

Both the dynamic kill and relief wells will require a great deal of effort and expertise to be successful. The rigs drilling the relief wells – the Rowan Gorilla V and Transocean’s Sedco 714 – are capable of operating up to 4.8 kilometers away from the Elgin Platform, said Jake Molloy, head of the RNT Union which represents thousands of offshore workers. The tricky bit, he said, will be to drill into the Hod formation with pinpont accuracy.

Erland Fjøsna a Bellona advisor and an expert in multiphase flow has noted that the dynamic kill effort could be thwarted – if not make maters worse – because of the phenomenon of slug flow.

Slugs are large quantities of liquid in a pipeline separated by relatively large gas pockets.

“Slug flow experiences extraordinary highs and extraordinary lows as the liquid slug reaches obstructions such as pipes and valves with great force,” said Fjøsna.

Bellona advisor Karl Kristiensen also noted that the dynamic kill operation posed a dilemma.

“Comprehensive risk assessment must be conducted, as we still have an active gas leak and no guarantee that the dynamic kill will work,” he said. “A balance needs to be found between stopping it or making it worse, as well as a modelling and analysis of the multiphase flow that will result.”

Kristiensen noted that the simultaneous relief wells being drilled could mitigate continued damage should the dynamic kill fail.

Their analysis was backed up by Norway’s Acona Flow Technology, which noted in an April interview with Tekniskukeblad that the top kill procedure could put undue pressure on already deteriorated pipes and lead to a far worse blowout than workers are currently struggling to contain.

“The challenge of a gas blowout is that the velocities of the gases and fluids that leak are high,” said Trygve Rinde, an expert in flow technology with Acona told the paper.

“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,” he said.  

Ultimately, these complications could lead to expanding the holes in the surface wellhead on the Elgin platform through which the gas is currently leaking.

“This is a pipe that is not designed to withstand such pressure,” said Rinde.