Much of Deepwater Horizon spilled oil gone

oilThe Deepwater Horizon oil spill appears to be largely over, with news that three quarters of the oil released during the approximately four months of the spill, has gone.

Most of the oil has evaporated, with what is left apparently being quite diluted.  Heavier remnants are either floating on the surface, or have washed up on beaches.

The well itself also appears to have been successfully sealed, with BP having used mud to contain the pressure, although further steps are required to make certain that the well is completely secure.

The following comments were gathered by our colleagues at the UK Science Media Centre.

Prof Malcolm Fox, Institute of Engineering Thermofluids, Surfaces and Interfaces, School of Mechanical Engineering, University of Leeds, said:

“The issue is that the oil which has been evaporated, burned or dispersed is the lighter/middle fraction of the spilt crude oil. The material remaining will be the heavier fractions which may agglomerate, e.g. as ‘tar balls’, which will take longer to degrade.

“A saving grace, if there is one, is that the Mexican Gulf crude appears to be lighter than, e.g., Middle Eastern, crude oils and there will be less of the heavy fraction in it and therefore less to deal with. Once widely dispersed, the bacteria in the warm Gulf of Mexico will readily feed on the heavy fractions left and degrade them.”

Prof Geoffrey Maitland, Professor of Energy Engineering, Imperial College London and spokesperson for Royal Academy of Engineers, said:

“This is very much in line with my own recent estimates and statements – that about 25% has been captured or burned, 25% vaporised due to the light nature of the oil or naturally bio/photo-degraded already. Another 25% finely dispersed by either waves/winds/tropical storms or dispersants, and either at or close to surface and ripe for degradation fairly quickly, leaving just 25% washed ashore as either oil, water-oil emulsion or tar balls, which will need further mechanical treatment and removal (with minimal use of chemicals if they are sensible… Despite what the EPA have said the non-biodegradable dispersants, which may hang around much longer than the oil and do adsorb on fish gills and other marine-life organs causing life-threatening problems, are in my mind a bigger longer-term environmental concern) but should be a manageable task in the months ahead.

“So, without minimising the extent of the damage caused by this 25%, 1.25M barrels, the combination of boom containments, skimming, good luck with winds and weather and partial collection and eventual capping of the well on July 15th have all combined to make the short-term damage far less than people feared and the prognosis for a relatively rapid natural clean-up good with the prospect of fishing, shrimping and natural habitats returning to close to normal on a timescale from months to 1-2 years max.

“The light oil and the warm temperatures of the Gulf of Mexico make this prognosis much better than was the case on the Exxon Valdez in cold Alaska for instance, with which comparisons have been drawn. The effect on oiling and deaths of birds has been similarly light compared with the Valdez and expectations (less than 2000 in each case – wind farms are more of a threat); the effect on marine life breeding will need to be seen in time – many sea turtle eggs have been rescued and relocated to hatch, and the fishing embargo will have enabled some re-stocking to counter some of the depletion caused by the oil/dispersants, but the long term effects will not be known for some time.

“So it is encouraging to see government agencies and reports confirming this more encouraging picture. US Government Energy Advisor Caroline Browner confirmed all this in an ABC interview today. So although Tony Haywood was not right to say that the spill was a drop in the ocean and the environmental impact would be very, very modest, in the way that he did, the facts behind these ill-advised comments are turning out to be reasonably consistent with their underlying sentiments and sub-text. Although the latest figures confirm that this is indeed the biggest offshore oil spill ever, about 75% of the 200M gallons has been prevented from causing major damage and the environmental impact has not turned out to be anywhere near as bad as was feared in the first month or so of this crisis, with various conditions combining to give a reasonably optimistic prognosis for a reasonably rapid natural clean-up of months to 1-2 years.”

Mr Simon Rickaby, Chair Of the IMarEST (Institute of Marine Engineering, Science & Technology) Pollution and Salvage Special Interest Group and Managing Director of Braemar Howells Ltd, said:

“The word ‘dissolved’ is totally wrong and misleading, the oil was not dissolved it was dispersed. Oil is insoluble in water but it can be broken down to such fine droplets that it appears to have “disappeared or dissolved away” but it is dispersed not dissolved!

“25% of the oil was removed through mechanical action (recovered from the well head, in situ burning and skimming). 3% being recovered by skimming is usual; it can be up to 10% for thicker oil but this is a light oil.

“Nature, or natural action, did its bit with 25% evaporated. The nice hot Gulf weather and warm seas combined with the type of oil in this spill will have helped. With the Exxon Valdez spill in Alaska, the cold weather, cold water and a different type of oil meant very little oil evaporated. The result was a large amount of pollution for a comparatively small amount spilt – 37,000 tons. In the case of the Sea Empress, of the 72,000 tons of oil spilt, nearly 30,000 tons evaporated, this was due to the type of oil. This is the equivalent of a ship load of petrol evaporating into the air and significantly less pollution compared to the Exxon Valdez despite the Valdez being the smaller spill.

“Another 24% was dispersed by nature or by dispersant as it was broken up in the washing machine ride from one mile deep to the surface after the dispersants had been injected at the source of the leak.

“So that’s 74% accounted for which leaves 26% still to be dealt with. These figures are very common in spills and it is also a classic example of the 80:20 rule, 80 per cent of the remediation is done in 20% of the time, whilst the remaining 20% is really tough and takes a very long time to get finished off! And where is this remaining oil? It’s in the reeds, salt marshes, mangroves and on the beaches or it’s still at sea – either floating on, in or near the surface, and that’s the problem. This needs to be dealt with.

“People are saying that BP is scaling back the operation while there is still oil to be cleaned up, but it is normal to stand down resources from one area where it is not required and put additional resources into areas where it is. If BP and the US Government are not putting the resources in to these areas then it could be for a good reason, such as mankind going in risks doing more environmental damage than if the oil was left to degrade and nature was left to recover by itself. However, this appears to the rest of the world as a “doing nothing option” and it is critical that if this is the case then it needs to be communicated to the public and if it is not the case then I would say get the resources in there now.

“Nothing is as simple as it may appear and until the investigation into the various failures and causes of the fire, explosion, rig sinking and the subsequent spill is complete, then no-one, including me, can say exactly what happened and we must keep an open mind.”

For more information, or for help finding a New Zealand expert on this topic, contact the Science Media Centre (NZ) on tel: 04 499 5476 or email: