Hydrocarbon gases estimated to have been 40% of the discharges from the BP oil well blowout

NASA Terra Satellite image of sun on the oil slick off of the
Mississippi Delta (highlighted by the tree-like structure in green)
on May 24, 2010

The BP oil well blowout last summer caused release of at least 50-100 million barrels of oil into the Gulf of Mexico.   In other units, this was somewhere between 7 and 14 million tons of oil.  This release was unusual geologically because the discharge rate was high compared to natural rates, it was extended (84 days), and it was deep (nearly 1500 meters).  It was also unique because it contained another 40% by weight dissolved hydrocarbon gases, mostly methane and pentane. I featured an article on natural vs. Deepwater Horizon seep rates by Cutler Cleveland on this earlier post. 

In a paper just released on-line by Nature Geoscience, Joye et al. have quantified this estimate of the amount of gas released, where it was released, and some of the implications.  The reference is Nature (published on-line) 13 February, 2011, DOI: 10.1038/NGE01067.  (I'll try to remember to come back and put in the formal publication reference!). I really like this paper--the authors dealt with some of the most atrocious scientific units possible to unravel this story: tons (or is it tonnes?), barrels, bopd's (barrels of oil per day), gallons ('a standard barrel of oil is 42 US gallons or 159 litres), BOE's (barrel of oil equivalent, in energy units of kilojoules or, in volume units, cubic meters or cubic feet),.... Definitely enough to drive an undergraduate chemistry class nuts for a few homework sets!  Well done!

The bottom line is that hydrocarbon inputs into the gulf were 5,000-10,000 tons of carbon per day from this single well, and that "contrasts starkly" with inputs from natural seepage (220-550 t carbon per day over the entire 70,000 square kilometers of the Gulf of Mexico. The hydrocarbon gases seemed to appear in discrete layers between 1,000 and 1,300 m depth, where concentrations were up to 75,000 times background levels. The ultimate fate of these hydrocarbons is uncertain at present. However, if the geologic record of the past is an indication, it is possible that bacterial activity and consumption of the methane could lead to formation of oxygen-depleted bottom waters.

The BP Well Operation and Their Problem with 'ice' Clogging

Image source: unknown

British Petroleum engineers have successfully installed a cover on the leaking well and are trying to siphon oil to surface ships.  They have been proceeding cautiously because their previous attempt with this procedure got clogged with a nasty form of ice called "methane hydrate" or "methane clathrate".

Water ice is capable of absorbing an amazing amount of some gases into its structure in "cages".  A typical clathrate cage is shown in the inset of this image of a methane clathrate burning.  Yes, you can set ice on fire!. The gas burns off leaving the ice structures behind. The gas molecules are stored in cages of H2O molecules, and it's quite amazing how much gas can be stored in these cages.

Clathrates are a major reservoirs of natural gas globally, as shown by the map of clathrate deposits.  The dissociation of this weird form of ice has been implicated in everything from the disappearance of ships in the Bermuda Triangle to sudden climate change.  It's been proposed that sudden "burps" of methane gases from clathrates in the Bermuda Triangle have changed the density of the water column so that ships that were floating on the water suddenly found themselves floating on "gassy water" and lost buoyancy, sinking to the bottom. (One thing nice about this blog is that I don't have to provide rigorous referencing!!)  55 million years ago, the Paleocene/Eocene boundary, there was a dramatic climate change that some have argued was due to a sudden methane influx into the atmosphere due to decomposition of clathrates.  The cause of decomposition is unknown, but theories relevant to the current climate crisis are abundant.  I found this article by Galvin Schmidt to be a thoughtful analysis.