Gulf Oil Spill Rate Must Be Much Higher Than Stated – 6 Million Gallons So Far?

Based on SkyTruth’s latest satellite observations today of the size of the oil slick and published data on the thickness of floating oil at sea that produces a visible sheen (1 micron, or 0.000001 meters) we think the official estimate of the spill rate from the damaged well has been significantly too low.

Immediately after the Deepwater Horizon rig sank on April 22, the Coast Guard estimated that the well was leaking 336,000 gallons (8,000 barrels) of oil per day. But for the past few days they’ve estimated the rate at 42,000 gallons (1,000 barrels) per day. We think it’s actually a lot closer to their original estimate.

We have a visible oil slick covering 2,233 square miles (5,783 km2). Given a minimum thickness of 1 micron (see chart below), that is 5,783 cubic meters of oil, or 1,527,706 gallons (36,374 barrels). The blowout happened almost 7 days ago on April 20. That’s at least 5,000 barrels of oil per day – assuming none of it was consumed during the two-day fire that raged before the rig sank on April 22, and none has been collected by the response crews that have been working diligently for days.

Our calculation also assumes the entire slick is a sheen barely thick enough to be visible. Yet the images we’ve seen so far, especially the ALI image taken on April 21, suggest a strong spectral response from the oil slick, and that in turn suggests a much thicker slick. Today a BP exec claimed that 3% of the slick was 100 microns thick, and the remaining 97% is only one or two molecules thick. We’re skeptical: 1 micron is the published, generally accepted lower limit for a visible sheen at sea:

CONCAWE chart of thickness and visible appearance of floating oil at sea. From a Minerals Management Service report, Real-time Detection of Oil Slick Thickness Patterns with a Portable
Multispectral Sensor.

So if 3% of today’s slick (173.5 km2) is 100 microns thick, and the remainder (5,609.5 km2) is 1 micron thick that’s a total of 22,960 cubic meters of oil: 6,065,390 gallons. That’s right: more than 6 million gallons spilled into the Gulf of Mexico so far.

This is what Dr. Ian MacDonald has to say. Ian is one of the world’s foremost experts in remote sensing of oil slicks, and has spent his career exploring the Gulf of Mexico:

It turns out to be pretty easy to roughly estimate the amount of oil in a floating oil spill — though like all estimates, large doses of caution should be applied. The critical variable is the thickness of the floating oil layer.

The CONCAWE guidelines from back in the late 80s are a reasonable place to start. CONCAWE gives a chart of thickness and appearance as shown in the figure. Notice that the minimum visible thickness is about 1um. If we take 1 um as a bare minimum starting place, think that a square meter of oil spill with a 1 um layer means that there is a 1000000/th of a cubic meter of oil floating in that spot. If you have 1 sq km of oil floating on the sea *and* it has a uniform thickness of 1 um, well, you have a million of those layers or 1 cubic meter. That makes 1000 liters of oil or about 264 gallons (6.2 bbl) per sq km of spill. We are seeing conservative estimates of 1000 sq km already on April 25th–I believe you measured 800 sq miles which is closer to 2000 sq km.

So for the minimum value on 25 April we have a minimum of 6,200 bbl of oil already on the water, which means that the 1000 bbl/day estimate we’ve been seeing is too low for an event that began on 21 April. However, this is probably a much too conservative estimate. This size in sq km of the floating oil spill may be greater by a factor of 2, as your estimate suggests. More important, the average thickness may be a factor of 10 or more greater. Certainly your more recent images suggest that the spill is locally dark and thick. Check the CONCAWE chart and you see that some of those sq km of ocean may represent 200 or 300 bbl of oil each.

So it would not be unreasonable to multiply that 6,200 bbl number by 20. This gets you up to 126,000 bbl in the water, which is about 5,300,000 gallons. That’s roughly half the total Exxon Valdez spill. I do not think I am being too alarmist here–but you should check my numbers.

It will be critical to get some more recent images to see how much the slick has grown in the past couple of days.



Gulf Oil Slick Growing – 2,233 Square Miles

MODIS satellite image taken this afternoon, April 27, shows growing oil slick in the Gulf.

We just processed a NASA/MODIS image taken from the Terra satellite this afternoon that shows slicks spread across 2,233 square miles, and within 22 miles of shore. See it here. The image suffers from clouds and haze (a problem we don’t have to deal with on radar images) so we used somewhat more sophisticated spectral processing to identify the oil slicks. And no, it’s not Photoshopped; we applied a modified Gaussian contrast-enhancement algorithm:

Spectrally enhanced version allows easier identification of oil slick on this cloudy / hazy image.

Gulf Oil Slick Dwarfs Response Vessels

Detail from SkyTruth image showing response vessels and Gulf oil slick on April 25.

We just got a detailed ALI satellite image from NASA that was shot two days ago, on April 25, when the oil slick was about 817 square miles in size (it has since more than doubled to at least 1,800 square miles). You can see several response vessels working at the periphery of the slick. The magnitude of the job they have to do is plain to see.

See more in our growing image gallery for this incident.

Gulf Oil Spill Covers 817 Square Miles

NASA/MODIS satellite image taken April 25 showing oil slicks from Deepwater Horizon disaster.

SkyTruth just processed a NASA/MODIS satellite image of the Gulf of Mexico that was taken early yesterday afternoon (April 25). Slicks and sheen (very thin slick) covers about 817 square miles, and reaches 50 miles away from the assumed point of origin (the site of the leaking well on the seafloor). We’ve posted this in our image gallery for this incident. We’ve also shown the last two positions of the rig that we were able to detect before it sank, as seen on NASA images from April 21 (also in our gallery).

UPDATE 4/27/10 1pm – We’ve added a very detailed image to our gallery, also taken on April 25, from NASA’s Advanced Land Imager (ALI) sensor carried on the Earth Observing-1 (EO-1) satellite. You can see response vessels, and gradations in the thickness of the slick and peripheral sheen. Meanwhile, the spill continues unabated, and the size of the oil slick has more than doubled since these NASA images were taken just two days ago. We hope to get new images soon.

Gulf of Mexico Oil Spill Getting Worse

Yesterday the Coast Guard reported that the damaged well on the seafloor in the Gulf of Mexico is leaking oil again, at a rate estimated to be 42,000 gallons (1,000 barrels) per day. This is bad news – it means the blowout preventer on that well is not doing its job, and that several attempts by BP, Transocean and the Coast Guard to operate a shutoff valve on the well using a robotic ROV have failed. The oil slick has grown rapidly and now covers 400 square miles.

Oil slick in the Gulf now covers 400 square miles. AP photo by Gerald Herbert, courtesy San Francisco Chronicle.

If the blowout and spill off Australia last year offer any lessons, it could be months before this well can be brought under control and the spill really and truly stopped. This is already a “major” oil spill by Coast Guard definition (>100,000 gallons), and a human tragedy. Economic losses include the $600-700 million dollar Deepwater Horizon drill rig, and as-yet untold millions in response and cleanup costs (and lawsuits from the people who have been hurt). But this blowout and spill in the Gulf now threaten to become truly catastrophic.

The NASA satellite imagery we used to track that Australia spill have been unavailable since Friday. As soon as we can get anything we’ll do our best to get it posted here.