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. 

Shell Oil Spill, Nigeria: FPSOs Coming to the US

Shell’s big oil spill off Nigeria yesterday reportedly occurred during the transfer of oil to a tanker in their Bonga offshore field.  Oil is produced in the Bonga Field using an FPSO – basically, a modified oil tanker anchored in place.  Oil collected from wells on the seafloor flows up through riser pipes connected to the FPSO.  Shuttle tankers take crude oil out of the FPSO’s storage tanks and carry it to coastal refineries. Here’s a schematic diagram showing the Bonga Field layout:

FPSO operation at Bonga Field off Nigeria. Image courtesy Offshore Technology.

In March 2011, federal regulators approved the first-time-ever use of FPSOs to develop an offshore field in the US Gulf of Mexico.  Petrobras got the nod for their Cascade-Chinook development in water 8,200′ deep, 160 miles off the Louisiana coast.  Their FPSO, a converted tanker called the BW Pioneer, holds 600,000 barrels of oil (25.2 million gallons). BOEMRE and Coast Guard divvied up oversight responsibility for this vessel / production facility with an MOU in 2009. This project got off to a very poor start when 8,500′ of riser pipe went crashing  to the Gulf seafloor back in early April.

Our main concern is that FPSOs are potentially sources of massive oil spills:  a serious blowout, fire or explosion, collision with another vessel, intentional attack, rogue wave or storm damage, or other incident could result in a near-instantaneous release of millions of gallons. And as we’ve said here before, despite the underwhelming oil cleanup results during last year’s BP / Deepwater Horizon spill, we’ve made no significant progress in our ability to handle big spills.

Shelling out the Oil in Waters off Nigeria: Radar Satellite Image December 21, 2011

Envisat ASAR satellite radar image showing large slick (black) from major Shell oil spill off Niger Delta.  Image taken December 21, 2011 at 9:30am local time.  Image courtesy European Space Agency.

Royal Dutch Shell’s Nigerian drilling operations in the highly productive Bonga Field were officially brought to a halt yesterday after “less than 40,000 barrels of oil” (1.7 million gallons) were reportedly leaked during a transfer of crude to a tanker. We’ve just processed a radar satellite image taken this morning (December 21, 2011) of the field, with the spill clearly visible.  Here it is showing the slick outlined in yellow; it is about 70 km (45 miles) long, 17 km (10 miles) wide at it’s widest, and covers 923 square kilometers (356 square miles) of ocean:

Another, much smaller oil slick appears at lower right; this looks like a bilge dump from a passing vessel, not related to the Shell spill.

Located 120 km off the the Nigerian coast, the Bonga Field is the first deepwater oil exploration and production project for the country since Shell began offshore drilling there in 2005. Shell’s onshore operations in the Delta have a long history of spills.


Map showing location of Bonga Field off Nigeria. Courtesy Marcel De Jong, Shell Deepwater Services Regional Study Team.

Chevron Oil Spill, Brazil – Small Slick December 6, 2011

Envisat ASAR radar image taken December 6, 2011. Image courtesy European Space Agency – click for larger version.

We’ve been getting a few Envisat ASAR radar satellite images of the Campos Basin off the coast of Brazil, covering the Frade field, where Chevron and their contractor Transocean experienced a loss of well control during drilling on November 7 that initiated an oil spill. Apparently “unexpected” reservoir pressure caused drilling mud to back up in the well, allowing highly pressurized oil (and probably some gas) to leak out into the surrounding bedrock.  This oil has since been working its way up to the seafloor through faults or fractures in the rock, emerging along a line of unnatural seeps on the seafloor, and floating up to the surface to create visible oil slicks.  The well was plugged a week after the spill began, and since then visible slicks have diminished in size.

Chevron may also be required by Brazilian authorities to drill a relief well to inject cement into the well at depth — an expensive proposition — to formally abandon the failed well.  And a Brazilian federal prosecutor based in Campos has filed a $10.8 billion suit against Chevron and Transocean, and is seeking to have both companies permanently banned from drilling in Brazil.

Meanwhile in Bohai Bay, China, ConocoPhillips has found little environmental damage from their spill earlier this year in the Peng Lai 19-3 field.  But they did reveal that their spill, like Chevron’s, was caused “due to unexpected pressure encountered while drilling.”  A mistake like that can lead to a blowout and major spill.  I hope all of the technical details from both of these incidents are being disclosed and will be made available to the public and to US regulators.

The radar satellite image above, taken on December 6, 2011, shows a very small slick originating near the location of Transocean’s SEDCO 706 drilling rig that was installing Chevron’s failed well. The slick is about 7.3 miles long and a few hundred yards wide, comparable to the slicks created by natural oil seeps in the Gulf of Mexico.  Wind conditions were good for slick detection at the time, blowing at about 10 knots (5 meters per second).  Several other small slicks are visible near a cluster of oil platforms (bright spots) about 50 miles south of the SEDCO 706.  This is within the southern Campos Basin, and these slicks may be the result of minor spills or leaks from platforms, pipelines, or vessels operating in one of the many offshore fields in the region.

Taylor / 23051 Chronic Leak Site in Gulf: Oil Analyzed

Back on September 15, a team from National Wildlife Federation piled onto a small boat on the Louisiana coast.  Their destination: the chronic leak site about 12 miles offshore where a cluster of wells operated by Taylor Energy has been steadily spilling oil into the Gulf since 2004.  Check out this aerial video of the site, shot by On Wings of Care on December 9, 2011:

Their objective: to collect samples of the Taylor oil slick for analysis, to see if it’s chemically distinguishable from the oil that gushed from BP’s infamous Macondo well about 30 miles away.  We wanted to know if other samples of oil collected in this region of the Gulf, on beaches and barrier islands and from slicks observed offshore, could possibly be coming from the Taylor site since it’s a well-documented source of oil pollution. The NWF team — coached in advance by Dr. Ed Overton at Louisiana State University on proper collection and sampling technique — succeeded. Dr. Overton analyzed the Taylor oil samples and in mid-October told us “these were heavily weathered oil with slight differences in the fingerprint pattern from the Macondo oil.”  (more after the jump….)

Elaborating on this a few days later, Dr. Overton said “the biomarker fingerprint is very similar but it does have significant differences especially in the 218 and 231 ion plots.  Also, the C2DBT/C2Ph and C3DBT/C3Ph ratios are not consistent with Macondo oil.  The sample we got from Ben Raines [of a small slick one mile from the Macondo well location] was very fresh with almost no weathering while the Taylor samples were all pretty heavily weathered with almost no normal hydrocarbons left in the GC data.  So, if you know what you are doing, you should be able to distinguish between Taylor sheens and other samples especially of the Macondo oils.  We really need samples of nearby seep oils and sheens from these seeps to get a full picture but so far, we have been able to fingerprint the Macondo oil fairly accurately (at least in my opinion).”

Here is a graphic Dr. Overton provided us yesterday, illustrating the difference in “weathering” of the Taylor oil samples from NWF compared with fresh Macondo oil samples taken directly from the riser pipe that connected the Macondo well with the Deepwater Horizon platform.  Dr. Overton said “While the data shown in the plots are not from the fingerprinting, these plots clearly show how much the Taylor samples were weathered compared to the Macondo Riser oil.  Getting good samples of all the slicks is a very daunting task because it requires close collaboration between surface sampling vessels and airborne observation. None the less, we still do not have good samples from sheens in the vicinity of the Macondo well.”

Data illustrating difference in weathering between oil samples taken from slicks at the Taylor/23051 chronic leak site, and from the riser pipe containing fresh crude from the Macondo well.  Graphic courtesy Dr. Ed Overton, Louisiana State University.
The upshot:  oil leaking from the Taylor site should not easily be confused with relatively unweathered oil from the Macondo disaster.  But it would be very helpful to collect more and better samples from the slicks being observed in the vicinity of the Macondo well site.
Eventually, as residual Macondo oil gets older and more highly weathered it will become more difficult to differentiate it from Taylor oil.