More scientists have come forward to criticize a US government report on the fate of the oil leaked into the Gulf of Mexico during the recent Deepwater Horizon debacle.

Earlier this month the National Oceanic and Atmospheric Administration stated that only 26% of the 4.9 million barrels that spewed from the BP well was “residual” in the Gulf. A number of scientists interviewed by Nature (see: Upbeat oil report questioned) and Science questioned the positive spin put on this report .

Now researchers from the respected Georgia Sea Grant programme have joined the fray. In their report they say that up to 79% of the oil from the spill remains.

“One major misconception is that oil that has dissolved into water is gone and, therefore, harmless,” says Charles Hopkinson, director of Georgia Sea Grant a researcher at thee University of Georgia Franklin College of Arts and Sciences (press release).

“The oil is still out there, and it will likely take years to completely degrade.”

At issue is the fate and danger of this distributed oil (a point also raised previously on this blog).

The NOAA report takes oil dispersed by chemicals or natural processes out of the ‘residual’ category, whereas the Georgia team leaves it in their ‘oil remaining’ category. Also, while NOAA puts evaporated and dissolved oil in one category, the Georgia report puts dissolved but not evaporated oil in the ‘remaining’ amount. The new report then tries to estimate how much of this distributed oil has has actually been completely degraded.

Another difference in the new report is a slightly lower overall amount of oil released. The Georgia team says 4.1 million barrels were actually released into the Gulf, as 800,000 were piped directly from the leaking wellhead to the surface. While this might seem a good thing, the smaller starting number means that higher percentage of oil remains in the system with this method of calculating (so maybe the top pie below should strictly speaking be bigger than the other pies, in the interests of graphical cohesion).

After all the endless doom, gloom and oiled pelicans, it’s nice to have a new entry in our (very) occasional series ‘good news from the Gulf of Mexico’.

First up: BP’s ‘static kill’ of the leaking well appears to have worked. This means the pressure of the heavy mud pumped into the well is successfully holding in the oil.

However the National Incident Commander, Admiral Thad Allen, said yesterday that the relief wells currently being drilled remain the ultimate solution.

“The static kill will increase the probability that the relief well will work. But the whole thing will not be done until the relief well is completed. The static kill is not the end all be all,” he said.

“… And there should be no ambiguity about that. I’m the National Incident Commander, and that’s the way this will end … with the relief wells being drilled, and the annulus and the casing being filled with mud, and cement being poured.”

In other news, the New York Times has apparently been given a new report due out later today from the National Oceanic and Atmospheric Administration. This report, says the paper, makes the staggering claim that “three-quarters of the oil from the Deepwater Horizon leak has already evaporated, dispersed, been captured or otherwise eliminated – and that much of the rest is so diluted that it does not seem to pose much additional risk of harm”.

The next sentence clarifies that most oil is either “light sheen” at the surface or dispersed below the surface. Whether huge amounts of dispersed oil in the ecosystem can really be said to not pose “much additional risk” is a controversial point. It’s probably better dispersed than as a huge slick of crude, but it is hardly business as usual for the sea.

In related news, the Guardian notes today that “the Obama administration is facing internal dissent from its scientists for approving the use of huge quantities of chemical dispersants to tackle the oil spill in the Gulf of Mexico”.

Image: a crewman from Coast Guard cutter Decisive observes the drilling rig undertaking the static kill / photograph by US Coast Guard Petty Officer 1st Class Adam Eggers.

The official estimate of the amount of oil that leaked into the Gulf of Mexico before BP managed to cap its ‘MC252’ well has again been revised upwards. The resulting new figure makes the incident the worst accidental spill in history.

US scientists now think that at the start of the disaster 62,000 barrels of oil a day were escaping the well, which began leaking after the explosion and sinking of the Deepwater Horizon drilling rig. Although this fell to 53,000 barrels per day by the time the well was capped on 15 July, a total of 4.9 million barrels probably escaped the well (press release).

Initially it was claimed that a mere 1,000 barrels per day were escaping (the history of the endlessly increasing estimates is contained in the original ‘it’s worse than you thought (again)’ blog post).

Of the 4.9 million barrels that leaked, some 800,000 were captured by BP, meaning ‘only’ 4.1 million barrels actually ended up polluting the Gulf. This is still more than the previous largest ever accidental spill – the Ixtoc 1 disaster, which released around 3.5 million barrels in the 1970s. Deliberate spilling during the first Gulf War is thought to have resulted in about 5 million barrels of spillage.

In other news, BP is still preparing for the ‘static kill’ of the well. This will involve attempting to permanently seal the well by forcing heavy mud downwards to drive back oil into the reservoir and allow the whole thing to be sealed off with cement. This is similar to the ‘top kill’ attempted earlier, except that the well is no longer flowing – hence ‘static’ (BP briefing).

If the static kill is successful a decision will have to be made as to whether to continue with the relief wells, which were previously thought to be the final answer to the leak.

Image: Q4000 vessel (shown centre) undertaking preparations for the ‘static kill’ / US Coast Guard photograph by Petty Officer 1st Class Adam Eggers.

Ships dealing with the aftermath of the disastrous Deepwater Horizon oil spill are fleeing the accident site today in the face of a ferocious storm.

Although BP is currently still monitoring the capped site of the MC252 well, efforts to drill relief wells that will finally shut it down have been suspended after forecasters predicted that Tropical Storm Bonnie would track into the Gulf of Mexico. According to the National Hurricane Center, the storm already has sustained winds of 65 km per hour and can be expected to worsen.

“Due to the risk that Tropical Storm Bonnie poses to the safety of the nearly 2,000 people responding to the BP oil spill at the well site, many of the vessels and rigs will be preparing to move out of harm’s way beginning tonight,” said Admiral Thad Allen, the National Incident Commander, yesterday.

“Some of the vessels may be able to remain on site, but we will err on the side of safety. While these actions may delay the effort to kill the well for several days, the safety of the individuals at the well site is our highest concern.”

Aside from the suspension of response work, a storm in the Gulf could have a number of potential impacts on the oil that has already leaked from the seabed. The storm could increase the mixing of oil and water, which would encourage the breakdown of the oil by natural processes.

In addition, a storm could either drive oil towards the shore or away from the shore, depending on which side of the slick it passed. For example, if a storm passed to the east, the wind – which blows counter-clockwise – would push oil out to sea.

At the moment the predictions for Bonnie have it heading more or less directly towards the leak site.

Image: National Hurricane Centre

BP has been given another 24 hours to test the sealing cap in place on its disastrous Gulf of Mexico oil well.

The National Incident Commander, Admiral Thad Allen, extended the test despite concerns regarding the monitoring systems in place and indications oil may be leaking from somewhere. A seep has been observed near the now-sealed well and there are also indications of methane over the well, says Allen.

Allen said yesterday that the pressure readings from the cap were lower than expected, possibly indicating that oil was leaking out somewhere. If necessary the valves in the cap can be opened, allowing oil to be piped to the surface for collection.

“This test will only continue if they [BP] continue to meet their obligations to rigorously monitor for any signs that this test could worsen the overall situation,” he said today. “At any moment, we have the ability to return to the safe containment of the oil on the surface until the time the relief well is completed and the well is permanently killed.”

BP says the relief wells currently be drilled to permanently shut down the leaking well will likely be ready in the first half of August.

Let’s just let BP say this in their own words: “Currently the well remains shut-in with no oil flowing into the Gulf.”

That’s right, after 88 days and probably over 3 million barrels of oil spewed into the Gulf of Mexico, the leak begun by the explosion and sinking of the Deepwater Horizon drilling rig may finally be under control.

BP appears to have successfully attached and engaged a ‘sealing cap’ atop the broken blowout preventer, stopping the oil flow. The company is now monitoring the pressure build up in the well to check if oil is escaping anywhere, and will reopen the valves and let oil flow to its collection ship after a test period. After this – if the test is deemed a success – the well could be shut off. (The BBC has a nice graphic explaining the details, and Admiral Thad Allen’s recent press conference also lays this out.)

The relief wells currently being drilled will still be needed, but staunching the flow of oil until they can be finished is a huge triumph for BP, which has already seen its share price respond positively.

Image: the sealing cap being deployed on 11 July / BP