Aug
11
2010

Water, water, everywhere, nor a drop of oil?

4.9 million barrels of oil, where did it go?

“It’s becoming a very elusive bunch of oil for us to find” – National Incident Commander Thad Allen

The federal government released a report last Wednesday claiming that about 75% of the more than 4.9 million barrels of oil spewed from BP’s blown out Macondo well has “evaporated or otherwise been contained.”

After reading which I thought: “...?..”

Really? Where did the oil go? The oil really evaporated?

Well here is a chart put out by the government via restorethegulf.gov:
Oil budget for BP's blown out Macondo well
Oil budget for BP's blown out Macondo wellCourtesy Restorethegulf.gov

The chart suggests that about one quarter of the oil that spilled from the well remains in the water, on shore, or in sand and sediments. One quarter of the oil is said to have evaporated or dissolved in the water, and the rest has been dispersed or collected (more on dispersion later).

OK…but, again, really evaporated? And why hasn’t all of the oil met the same fate? Why did some of the oil evaporate while some dissolved, and still other bits formed tar balls and washed ashore?

The answer, it seems, is that, according to Oil in the Sea III, a report published by the National Academy of Sciences, oil is a mixture of hundreds of compounds--including benzene, toluene, and heavy metals--the composition of which varies from source to source and over time. The hours-long journey that the oil makes from the well head to the ocean surface causes the oil to fractionate into its component chemicals, leading the heavier compounds to drift to the ocean bottom while the lighter compounds rise to the ocean surface.

Once at the surface, the lighter hydrocarbons, also known as light ends, are more prone to evaporation than are the heavier components. Rough seas, high wind, and high temperatures increase the rate of evaporation and the proportion of oil lost this way. The warm, turmultuous water of the gulf has therefore promoted evaporation of the lighter fractions of the spilled oil.

Some of the “hundreds of compounds” in oil are water soluble and dissolve into the surrounding water, a process that occurs more quickly when the oil is finely dispersed. The more soluble compounds turn out to also be the light aromatic hydrocarbons. Thus, the processes of evaporation and dissolution are lumped into one pie of the chart.

What about the 16% of the oil that has “naturally dispersed”? Like with dissolution and evaporation, the character of the oil and the state of the sea influence how much oil is naturally dispersed. Waves and turbulence at the sea surface can promote natural dispersion, causing an oil slick to break up into droplets which then become mixed into the upper levels of the water column. Dissolution, biodegradation, and sedimentation are more likely when the oil remains suspended in the water as droplets. Again, light, low viscosity oil is most prone to natural dispersion.

So the oil that has dissolved or dispersed (naturally or chemically) is not really gone. It is still in the water, it just can't be seen.

Also, unfortunately, some researchers remain wary that oil that has disappeared from the water's surface will reappear onshore in the future, as happened with the 1979 Ixtoc I oil spill. Larry McKinney, director of the Harte Institute for Gulf of Mexico Studies at Texas A&M, Corpus Christi, told Discovery News that dispersants similar to those used on the BP spill were used to break up the Ixtoc oil, which later washed ashore onto Texas beaches. McKinney is worried that the same thing will happen with this spill. "BP used a lot of dispersant and the oil went someplace," he said.

I am quite curious about the use of chemical dispersants with this spill and the microbes that are doing the degradation, so I am writing a post about it. If you are curious too, check out Petroleum to clean up petroleum? on the Buzz blog.

One last thing:
According to the New York Times, reaction to the report (and its associated chart) has been varied among scientists specializing in the issues it raises. In fact, Samantha Joye, a marine scientist at the University of Georgia told the Times that a lot of the report’s content is “based on modeling and extrapolation and very generous assumptions.” She said that the report would have been “torpedoed into a billion pieces” if it had been put out by an academic scientist.

On the other hand, Edward B. Overton of Louisiana State University said that the report might have underestimated the amount of oil that has effectively left the Gulf. See the Times for a full examination of the debate and the applicability of modeling for predicting the amount of oil that remains.

Your Comments, Thoughts, Questions, Ideas

rationalist's picture
rationalist says:

Here's the problem.

The bacteria that eat the oil leach oxygen from the ocean. This poses a serious problem to marine life.

So the real kick from this spill is not gone, but on the horizon.

posted on Wed, 08/18/2010 - 7:42am
Anonymous's picture
Anonymous says:

are you sure that it doesn't kill humans too?

posted on Tue, 09/21/2010 - 11:09am
isabel's picture
isabel says:

why are peolple so mean to nature?

posted on Mon, 08/23/2010 - 2:01pm
rationalist's picture
rationalist says:

BP is entirely to blame for this disaster. They knew they were drilling in a highly dangerous area and they knew the type of work they were doing was risky. Rather than submit to American drilling standards, BP leased Deepwater Horizon to the Marshall Islands so they could rush the rig through inspection.

Even after all this, they chose to intentionally use defective parts and refuse to stop drilling to fix their equipment. And this was the rig that was supposed to be among the safest in the world!

When an employee of a drilling company can predict his own death and arrange the necessary paperwork *before* he dies in an industrial accident, you know something's wrong.

Eleven people were killed when the Deepwater Horizon exploded. Tony Hayward and those who aided and abetted him deserve to be tried for criminal negligence.

posted on Mon, 08/23/2010 - 4:14pm
Anonymous's picture
Anonymous says:

BP is to blame for this massive spill... they should of had all their things straight.

posted on Sat, 09/11/2010 - 2:25pm
carrol's picture
carrol says:

i don't know how the oil spill happened. bp said,that they are going to clean the oil up. right now the leak is coming into an end. i saw this on the news.

posted on Sat, 09/18/2010 - 5:44pm

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