Gulf Oil Spill – New Spill Calculation – Exxon Valdez Surpassed Today

Figure 1. US Coast Guard map showing size and appearance of oil slick on April 28, 2010.

Dr. Ian MacDonald at FSU just produced a new spill-size estimate based on the US Coast Guard aerial overflight map of the oil slick on April 28, 2010. This map shows the slick covering 1,786 square miles (4,627 square kilometers). The bottom line: on April 28 there was a total of 8.9 million gallons floating on the surface of the Gulf.

That suggests a minimum average flow rate of slightly more than 1.1 million gallons of oil (26,500 barrels) per day from the leaking well on the seafloor. Since we’re now in Day 11 of the spill, which began with a blowout and explosion on April 20, we estimate that by the end of the today 12.2 million gallons of oil, at a minimum, have been spilled into the Gulf of Mexico.

The oft-quoted official estimate for the Exxon Valdez spill is 11 million gallons, although some think that is the lower limit of the likely range. It appears that we’ve just set a very sad new record.

Here is Dr. MacDonald’s calculation:

Deepwater Horizon spill estimates derived from USCG fly-over data (28 April 2010)

These estimates of the total volume of oil released by the Deepwater Horizon spill were derived from the USCG fly-over map (Figure 1). The map was geo-referenced in Arc Map and the areas of each of the slick types (dull oil streamers, etc) were measured with a planimeter tool. Thickness estimates for each slick classification were taken from the BONN guidelines as published in the NOAA field manual (Figure 2). Conservative values were used for each slick types. Note that the predicted average layer thickness are still very small.

Figure 2. Chart of oil thickness and appearance.


A human hair is approximately 100 µm (microns). The main slick, which corresponds to
the cross-hatched area was assigned a low value of 0.5 µm. We calculate a total volume of oil for this slick as 8.94 million gallons (212,000 barrels) (Figure 3). Considering that the oil in the water on April 28 has been deposited since the blowout and explosion on April 20, the flow rate should be on the order of 26,500 barrels per day. Some fraction of the total oil released will have been evaporated or emulsified and sunk in the time since the spill began, or collected by the response crews, so this should be considered a minimum estimate.

 

Figure 3. Volume of oil based on Coast Guard map (Figure 1) and thickness (Figure 2).

UPDATE 5/1/10 5:15 pm – Lots of cloud and haze but this afternoon’s MODIS satellite image shows the main body of the oil slick around the leaking well location.


Gulf Oil Spill – 2 Million Gallons – Per Day?

The Mobile, Alabama Press-Register has published an article by Ben Raines with an alarming prediction. If the leaking well in the Gulf of Mexico shrugs off all control – the crippled blowout preventer, the wellhead, and any remaining control valves or baffles impeding the flow of oil and gas through the well – the rate of spillage could go to a whole other level: as much as 2 million gallons (150,000 barrels) per day.

Schematic diagram of the leaking well and the relief-well drilling plan. Courtesy Times/Picayune.

This worst-case scenario is based on the fact that there are individual wells in the Gulf of Mexico that produce 1.26 million gallons (30,000 barrels) of oil per day. That’s a controlled rate of flow. If all control were removed, the flow rate would be higher. How much higher?

“Typically, a very good well in the Gulf can produce 30,000 barrels a day, but that’s under control. I have no idea what an uncontrolled release could be,” said Stephen Sears, chairman of the petroleum engineering department at Louisiana State University.

 

Gulf Spill – Oil Is Hitting The Shore

We just learned that oil is now beginning to wash up on the beaches of the Mississippi Delta. This afternoon’s clear-sky NASA/MODIS satellite image shows the full extent of the slick, with oil covering 2,256 square miles:

Satellite image from early afternoon of April 29, 2010 shows oil slick very close to shore.

Today SkyTruth’s president did an interview on CNBC. You can watch it here; our bit starts at about 4:20.

Gulf Coast folks, YOU CAN HELP show the world what’s happening by joining the new Flickr group, Gulf of Mexico Oil Spill 2010. Upload your photos, video and observations to let everyone know the impacts of this spill. Learn to geotag your work, and we’ll be able to pinpoint it on an interactive map.

Gulf Oil Spill – Bigger Than Exxon Valdez

Just five months ago, SkyTruth’s President testified to Congress about the risks posed by offshore drilling. Now we’re seeing a catastrophic spill in the Gulf that could soon surpass the sorry benchmark set 20 years ago by the 11-million-gallon Exxon Valdez spill.

SkyTruth is beginning to get radar satellite images showing the oil slick from the Deepwater horizon blowout and spill in the Gulf of Mexico. These images, from a variety of non-US satellites (don’t get us started on that), cut right through clouds and haze to show the “texture” of the ocean surface. Oil flattens the ocean out (that’s why they call it a “slick”); flat water looks black on radar images. This image, acquired by the European Space Agency’s Envisat satellite, clearly shows the sprawling slick at about noon local time on April 26:

Satellite radar image taken April 26 clearly shows oil slick (lower right) from Deepwater Horizon spill. Source: European Space Agency.

This, and other radar images that SkyTruth is getting, confirm what we’ve seen on the NASA/MODIS images so far, and support our conservative calculations showing that in the first week of this spill at least 6 million gallons have entered the Gulf. That’s a spill rate of at least 850,000 gallons (20,000 barrels) per day, 20 times larger than the official Goast Guard estimate of 42,000 gallons per day.

The Australia blowout and spill took 10 weeks to control.

The Exxon Valdez tanker spill totaled 11 million gallons. We could exceed that in just a few days, if we haven’t already.

UPDATE 4/28/10 9:30 pm – A NASA/MODIS satellite image taken this afternoon has clouds, jet contrails and haze that obscure much of the oil slick, but shows the western edge of the slick is within 10 miles of shore.

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.