Oil Pollution off Nigeria – Other Sources?

After flying journalists over the remnants of the Bonga FPSO oil spill off Nigeria,Shell pointed out that they are not the only polluters in this part of the world, and will clean up another small spill in the area not related to any of their operations.

That certainly doesn’t excuse their (much larger) mess but they are correct:  satellite images of the west coast of Africa, like some other coastal regions around the world, routinely show signs of oil pollution from other sources, especially bilge-dumping by vessels large and small. We don’t know if it’s legal in this area; it is not legal in US or Canadian waters. Radar satellite imagery is an excellent tool for detecting bilge-dumping.

This Envisat ASAR image taken on December 18, 2011 shows a 100-mile-long slick caused by bilge dumping from a large vessel that was traveling toward the southeast on a course taking it very close to the Bonga FPSO (we’ve inferred the location of the FPSO from multiple radar satellite images; if anyone has the exact lat/lon coordinates please pass them along to us):

Envisat ASAR image taken December 18, 2011 showing oily bilge dump from a passing vessel northwest of the Bonga oil field off Nigeria. Image courtesy European Space Agency.

At 1 micron thick this bilge slick holds about 80,000 gallons of oily material.  Projecting the vessel track back to the northwest, we land near the city of Aneho on the Togo coast. There is an industrial facility in the area that appears to have an offshore loading system.  It could be the point of origin for the suspect vessel, but we really have no way of knowing:

Projecting backward along bilge slick to shore. Envisat ASAR image courtesy European Space Agency.

Here’s what it looks like in Google MapsDoes anyone have any information about this facility?

Shell Oil Spill off Nigeria – How Big?

Shell has declared victory over the major oil spill from their Bonga FPSO off Nigeria, claiming the slick was halted 12 miles offshore and has mostly dissipated, thanks to evaporation plus the use of chemical dispersants. Our observations of satellite images over the past few days don’t indicate anything to the contrary.

How big was this spill?  We think the amount spilled is near the high end of Shell’s estimate of “up to” 1.68 million gallons, based on the size of the oil slick observed on December 21 and the photos provided by Shell showing a rainbow sheen.  The thickness of “rainbow sheen” is in the 5 to 10 micron range according to the CONCAWE guidelines, and 0.3 to 5 micron range according to the BONN convention. The overlap — 5 microns — would mean a spill of at least 1.2 million gallons (28,571 barrels).

On their website Shell reported the slick was “less than a hundredth of a millimeter” thick in most areas. 1/100th of a millimeter is 10 microns, which would be a spill of 2.4 million gallons — 58,000 barrels.

Assuming Shell, like most successful companies, is fanatical about inventory control they should be able to provide an accurate measurement by comparing the amount pumped out of the FPSO with the amount that actually ended up in the shuttle tanker. Flow meters on the pumps and transfer lines, and gauges in the tanks, should allow them to calculate the spill with precision.  Let’s ask them for those numbers and settle the question.

Regardless of the specific amount spilled, we’re left with some troubling questions, most notably: how could up to 1.7 million gallons of oil steadily leak into the ocean before anybody noticed and took action? The crack in one of the transfer lines that Shell blames for this leak looks like it could only divert about 5-10% of the flow through that line. How long would that take to amount to 1.7 million gallons?  This is just the latest example of the many mundane, low-tech ways that modern offshore oil production still poses risks — even when it’s being done by one of the biggest, technically accomplished, retail-brand-sensitive multinational oil companies (hmm, that sounds familiar…).

Shell Oil Spill – Moving Toward Nigerian Coast

Yesterday’s MODIS satellite images were a bust, but today’s were slightly less cloudy/hazy.  Both the Terra and Aqua images show a pale patch of ocean water about 18 kilometers offshore, covering a total area of about 678 square kilometers.  But this is a tough call – the image quality really isn’t very good.  The closest sizable populated area near this part of the coast, according to Google Earth, is the town of Burutu located at top center on this graphic:

MODIS/Terra satellite image taken December 23, 2011 at 10:10am local time. Possible location of oil slick noted. Image data courtesy NASA/MODIS Rapid Response Team.

This fuzzy patch that may or may not be the remnants of the oil slick is located about where we would expect to see it, given the wind speed and direction over the past couple of days (blowing from the south-southwest at 5-10 knots). Radar imagery would give us a better look but we haven’t seen any new radar images since December 21.

So far we haven’t heard that any oil has come ashore.  Shell reports they have mounted a vigorous response, including the use of chemical dispersants to break up the oil slick.

Yesterday Shell also released this photograph showing what purportedly caused the leak – a small crack in a transfer line at their FPSO.  Engineers, tell us – how long would it take to spill >1 million gallons of oil from a relatively small break like this?  I don’t know the diameter of this line; possibly 20″ or so?

Photograph reportedly taken by ROV showing crack in transfer line. Photo courtesy Shell.

Let us know if you have any expertise on flow rates through pipelines, and are willing to provide some expert opinion on this.

Shell Oil Spill off Nigeria – Questions….

We’ve got a few questions for you savvy engineers out there about Shell’s spill during loading at their FPSO in the Bonga field off Nigeria.  Based on the size of the oil slick on satellite images yesterday, and photos of parts of the slick released by Shell along with statements made on their website (scroll down to read the comments), we think that the spill may be near the high end of Shell’s public estimate of up to 1.7 million gallons (40,000 barrels). 

According to Shell, this spill occurred during the transfer of oil from the FPSO to a tanker.  Oil from the FPSO was being pumped into the tanker. Or as it turns out, was being pumped into the water. So here are the questions: 

  1. How long does it take the workers onboard to notice that, hey Houston, we’ve got a problem here?
  2. How long does it take to shut off that pump? 
  3. How long would it take to pump 1.7 million gallons of oil into the water? 

Please let us know by commenting on this post if you have any expertise in this area and can help shed some light on how a spill of this size could have occurred during the routine transfer of oil from an FPSO to a tanker.

Nigerian authorities are predicting that oil will begin to come ashore this afternoon.  

Another Satellite Image of Shell Oil Spill in Nigeria

Less than an hour after Envisat captured a stunning radar image of Shell’s big oil slick off Nigeria, NASA’s MODIS satellite flew over.  The Terra instrument on MODIS took this visible-infrared image that also shows the oil spill peeking through the clouds and haze that typically obscure this part of the world:

Detail from MODIS/Terra satellite image showing oil slick off Nigeria on December 21, 2011 at 10:15-10:20 am local time.  Image courtesy NASA/MODIS Rapid Response Team.

The slick coincides exactly with the slick on the radar image – no surprise there – but it does appear slightly smaller. On this MODIS image, the slick is showing up as a spectral feature, a target with a distinct reflectance signature typical of floating oil (high reflectance at shorter wavelengths, making it appear pale blue-ish in color).  On a radar image, oil slicks are textural features: they smooth out the ocean surface, causing specular reflection of the incoming radar energy being beamed down at earth by the radar instrument. The very thin edges of the slick look transparent to MODIS but are still able to smooth out the water and appear dark on radar images under suitable wind conditions.  Scatterometer data show that the surface wind speed was probably in the 5 to 10 knot range, ideal for slick detection on radar.

Which brings us to the amount of oil spilled.  Shell has reported “less than 40,000 barrels” were spilled, so the amount could be anywhere from 1 gallon to 1.7 million gallons.  Based on the radar image today, the oil slick covers 923 square kilometers.  At an average thickness of 1 micron (1/1,000th of a millimeter) that would amount to 243,672 gallons (5,802 barrels) of oil.  But portions of the slick could be many times thicker than that; it’s not unusual for a spill directly to the sea surface to be millimeters, or even centimeters, thick.  Estimating the thickness is usually based on direct visual observations of the slick, especially the color.

It would be very helpful to get photos or video of this slick taken from the air and on the water.