Oil Spills for Dummies

So, at a Sunday news briefing, British Petroleum's CEO, Tony Hayward, announced that there are no underwater plumes of oil resulting from the April accident at the company's Deepwater Horizon rig in the Gulf of Mexico.

Why? Well, first BP's testing hasn't found any such evidence. And second, Hayward reminds us that, you know, oil floats. Or if we didn't get that: "Oil has a specific gravity that's about half that of water. It wants to get to the surface because of the difference in specific gravity."

Let's give the man this: there is definitely oil floating on the surface waters of the Gulf of Mexico. Actually - as this photo featured on MSNBC demonstrates - it's kind of hard to miss"


But also let's look past the Oil Spills For Dummies approach regarding those underwater plumes. Because Hayward, as it turns out, refused to give any information about the BP water analysis that found no evidence of oil plumes beneath the surface.

This despite the fact that independent researchers from at least four universities have identified underwater plumes of oil using research boats, submersible vehicles, and even sending divers into the plumes. The University of South Florida reported a plume of near transparent, oil-infused water stretching some 20 miles from the site of the oil ring. Similar results have been reported by the researchers from the University of Georgia, the University of Missippippi, and Louisiana State University.

Although maybe he was just trying counter the sense of depression that seems to be resulting from those encountering underwater plumes? "Every fish and invertebrate contacting the oil is probably dying. I have no doubt about that," Prosanta Chakrabarty, a Louisiana State University fish biologist, told the Associated Press.

If so, it would have been helpful if he would been a little more careful of his facts - or at least made the assumption that we were smart enough to vet them. Because as it turns out, deep water physics tell us that oil leaks coming from about a mile below the surface - as with the Deepwater Horizon - actually don't come so readily to the surface.

That's because at greater depths, thanks to a combination of pressure, lower temperatures and increased salinity, water acquires greater density. In fact, this increased density of water can achieve a kind of equality with the naturally buoyant hydrocarbons in oil. Scientists call this a neutral buoyancy state and what it means is that instead of floating to the surface, the pressures exerted in deep water cause the oil to mix instead into subsurface waters.

But beyond the physics of deep water spills, BP itself may also be creating these underwater plumes by its heavy use of chemical dispersants to break up the slick of oil on the surface. As countless studies show, as dispersants break the oil into tiny particles, those the fragments tend to sink below the surface where - if all goes to plan - they are engulfed by oil-digesting microbes and degraded into more harmless materials.

As one industry group, the International Tankers Association, states: "If dispersion is successful, a characteristic brown plume will spread slowly down from the water surface a few minutes after treatment."

The creation of dispersed oil plumes isn't exactly a secret to our government either. For instance, here's a handy document created by our own National Oceanic and Atmospheric Administration (NOAA): The Dispersant Application Observer Job Aid. And - surprise - it includes includes photo after photo of plumes created by spraying disperant onto surface oil.

None of these are as stark as the photo of oil oozing across the wave-tossed surface of the Gulf. In fact, the image provided by the tanker association is rather beautiful:


But you can see in it the white cloud of dispersant, which has not touched oil, in the water and the shadowy plumes forming under the darker oil slicked on the surface, where the dispersant has done its job. And you do have to wonder, don't you? At least, I wonder how dumb Mr. Hayward thinks we are.

Of course, he also declared that the fisherman reporting illnesses after cleaning duty in the Gulf were just suffering from food poisoning. Hands up if you believe that one.


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Interesting article and shame on Mr. Hayward by talking down to people and looking like a fool in his own field. That being said, could you hold off on the "evil multinational corporation" rubbish? It really undermines your credibility. Believe it or not evil multinationals are staffed by real people, and there are a lot of employees of BP and other companies down there trying their damnedest to stop this. It might not fit with the simple worldview that seems so popular here, but some of those employees care about the environment and are just as sickened by this as you or I or anyone in journalism or academia.
Yes, the incompetence and greed that resulted in this is an exhibit of the banality of evil. But don't paint everyone in the industry with the same brush. There are a lot of people who did their jobs that don't deserve the backlash.

By Tamakazura (not verified) on 31 May 2010 #permalink

Tony Hayward: "Oil has a specific gravity that's about half that of water."

That is false. From http://en.wikipedia.org/wiki/API_gravity:

Crude oil is classified as light, medium or heavy, according to its measured API gravity.

* Light crude oil is defined as having an API gravity higher than 31.1 °API. (less than 870 kg/m3)
* Medium oil is defined as having an API gravity between 22.3 °API and 31.1 °API. (870 to 920 kg/m3)
* Heavy oil is defined as having an API gravity below 22.3 °API. (920 to 1000 kg/m3)
* Extra heavy oil is defined with API gravity below 10.0 °API. (greater than 1000 kg/m3)

Pretty far from 500 kg/m3...

Deborah Blum: "That's because at greater depths, under greater pressure, water acquires greater density."

But in that case the oil would surface even faster! More likely the underwater plumes are from the heavier fractions of crude, possibly mixed with mud.

By Lassi Hippeläinen (not verified) on 31 May 2010 #permalink

Yeah, it was a cheap shot, meaning it was fun to write. But you're right that it was a little off the rest of the piece. So I took it out - thanks for writing.

Hi Deborah,
Thanks for helping us sort through the media muck on this ever-growing disaster.

One question: Since using dispersants on an oil spill this size seems to be causing at least as much harm as good, is there a way to go the other route? That is, congeal or solidify the oil enough that it can be scooped up? Can it even be turned to a plastic by adding some sort of chemical agent (since many plastics come from oil anyway)?

I realize I'm showing a lot of ignorance about the chemistry of oil, etc. with this question. But that's why I came to you, my "resident" chemistry expert!



That's a great question, Chris. Wish I'd thought of it. I haven't been able to find a plasticizer on the EPA list of approved products for cleaning up oil spills: http://www.epa.gov/emergencies/content/ncp/product_schedule.htm

It may be a tricky kind of balancing act. We know, for instance, that spilled oil eventually will naturally "weather" to a thick tar - yes, tar balls - that can be scooped up. But once oil forms into a tar, it becomes near impossible for bacteria to break it down. Microbes do better with the tiny droplets created by dispersants. On the EPA list, you will see "surface washing agents" that are used to help clean up oil tars.

Also, if you read through the EPA list you'll see that aside from dispersants and washing agents, there are also quite a few bioremediation agents. These consist of either souped-up microbial colonies to intensify the attack on the oil or nutrients to stimulate bacteria already in the water as they move to digest the oil. There's been no indication that BP has tried this approach, although I have read that there's some hesitation about adding nutrients because of algae-bloom concerns.

There may be innovative companies out there, of course, with products not on the EPA list, such as your plasticizer idea. I'd love to know about it. But I have a feeling that, if so, we'll be digging out that information rather than hearing about it from the, um, authorities.

Hope this helps!

Wow! Thanks for reading my comment :)
I have been reading articles over at the oil drum--they are pretty good at explaining what went wrong. They are a little sparse on the cleanup side, though which is why your article is nice.

By Tamakazura (not verified) on 01 Jun 2010 #permalink

We now have the government saying that the leak will continue till August. Or maybe even until the entire well has emptied itself.

What exactly is the situation? A pipe has been drilled into the well, and now is gushing out oil into the ocean bed.

Solution: Dig a shaft, say about a mile deep next to the pipe (shouldn't take more than a few days to do). Detonate a very powerful bomb, maybe even a nuclear bomb. The oil will no longer have a clear path to the surface and the leak will stop.

As I understand it, the two factors which affect density of sea water are temperature and salinity. I don't think increased pressure at depth has anything to do with it. Rather it cold down there, and more saline waters tend to sink. Is this the case?

By Jim Thomerson (not verified) on 03 Jun 2010 #permalink

Well, pressure is also a factor. But after you wrote, I did a little more research and you are absolutely right that temperature and salinity are the most important factors in increasing water density at depth. I tweaked the post slightly in response to make it more accurate. So thanks for writing! And for those who want to know more on the subject, there's a very clear explanation here:


"or at least made the assumption that we were smart enough to vet them"

Here are a couple of questions for an unscientific survey:

1) How many folks saw the soundbite where Mr. Hayward made his comment?
2) How many folks thought to themselves "oh yeah, oil floats on water"?
3) How many folks have the interest, initiative, or the slightest clue to actually research the accuracy what Mr. Hayward said?

My answers:
1) a big number
2) a slightly smaller big number
3) statistically speaking, zero.

In the calculus of corporate PR, Mr. Hayward wins.

But perhaps I'm too cynical.

By Theobroma Cacao (not verified) on 03 Jun 2010 #permalink

We don't know the composition of the crude oil as it is leaving the well head. This crude is reported to have a very high methane content. At 2500 psi and 0 C, the density of methane is 0.164.

If the oil was ~50% methane, it could have a density half that of sea water.

Excellent point and, yeah, that would definitely make a difference. I really appreciate the knowledge you bring to these comments.

I'll bet we both would like to have more information at this point. My object here, mostly, was to point out that contrary to Hayward's statement, oil does not inevitably float in all situations and that there are a couple specific issues with the Gulf spill in particular that might, in fact, encourage formation of underwater plumes.


If the solution gas oil ratio was very high, most of the methane (as well as other lighter hydrocarbons like ethane etc) would not be dissolved in the oil - it would be free gas at the approximately 2500 psi pressure at the sea floor. In fact, the free gas was what prevented the first attempt to put something over the well to collect the escaping oil. The free methane was forming hydrates and causing the dome to float free of the well.

Using the Vasquez Beggs Correlation in my "Saphir" well test analysis software and assuming an oil API gravity of 45 (very light) and a gas gravity (relative to air) of 0.6 (which is very light for solution gas) gives a density for gas saturated oil at 2500 psi and 5 Celcius of 663 kg/m3. The density of seawater (salinity of 35000 ppm) at this temperature and pressure is 1027 kg/m3. This gives a density ratio of 0.65. I suppose this could be considered to be about half. However, as the oil rises and the pressure drops, the oil becomes denser as the lighter hydrocarbons flash off and Hayward becomes fuller of crap.

Anyone know what Hayward's background is (Engineer, Geologist or Bean Counter). A blowout like this is what happens when the bean counters start to over rule the engineers. From what I have read at The Oil Drum the likely culprit is a bad cement job on the production casing. They did not run a cement bond log before starting to replace the drilling mud in the pipe between the wellhead and surface with lighter seawater so they could move off of the well to allow the completion platform to come in. They did not give the cement a lot of time to set either.

By Militant Agnostic (not verified) on 04 Jun 2010 #permalink

Hayward actually has a PhD in geology from the University of Edinburgh. It isn't showing much though, is it?

If the oil was ~50% methane, it could have a density half that of sea water.

We don't know the composition of the crude oil as it is leaving the well head. This crude is reported to have a very high methane content. At 2500 psi and 0 C, the density of methane is 0.164.

Out sight out of mind?

Can somebody tell me what the density of the oil was in the BP well?

If it is less than that of the ocean water how can it sink?

Does the dispersant effect the density of surface waters?

Béla Lipták, PE
Lipták Associates, PC
84 Old N. Stamford Rd.
Stamford CT 06905
T: 203-357-7614
F: 203-325-3922
E: liptakbela@aol.com

By Béla Lipták (not verified) on 30 Jul 2010 #permalink