Oil seepage an inconvenient truth-npa seep information - gom portion
1. OIL SEEPAGE: AN INCONVENIENT TRUTH
(OR THE PERCEPTION OF RISK IN OIL
PRODUCTION)
DR GEOFF LAWRENCE, TREICO LIMITED
MAY 14TH 2010
The information and illustrations are drawn from web searches and personal
knowledge. The author acknowledges the close collaboration with Fugro-NPA,
but this perspective is strictly that of the author.
2. Just 100km from Macondo, the Gulf of
Mexico’s natural seepage-slicks are so dense
and persistent, they are observed on 1km
resolution MODIS
3. Oil is being squeezed out of the GoM’s
sediment like a sponge
4. Green Canyon is a cauldron of seeping oil
The liquid oil seepage of the Green Canyon region of the Gulf of
Mexico is the densest and most persistent on the planet and
definite seepage-slicks are readily observed on most cloud-free
remotely sensed images, because slick reflect in all
wavelengths. Seepage-mapping criteria were developed over
persistent oil seepage here and in California’s Santa Barbara
Channel, using, for example, Landsat optical images. The
cluster of nested slicks in the Green Canyon region on the
MODIS image is distinctive. Satellite synthetic aperture radar
(SAR) images have fine resolution and penetrate night and
cloud to image slicks consistently at low to moderate sea state.
5. Gulf of Mexico deepwater oil slicks
1.
2.
3.
Green, red and pink are natural seepage-slicks mapped on
satellite SAR. Dense repeating seepage coincide with many fields
5
6. Gulf of Mexico deepwater oil slicks
1. Green Canyon and adjacent area: dense prolific and recurring
seepage-slicks
2. Campeche Knolls: asphalt volcanism like that off Coal Oil
Point, at 3000m depth, coinciding with seafloor hydrate
mounds and dense recurring seepage-slicks vertically above
(See IR MacDonald, et al. Science, 304 14 May 2004 999-1002)
3. Natural seepage and heavy pollution; site of the IXTOC blow-
out 1979
Typical Green Canyon slicks illustrated on next two slides
7. Natural tar mats
Prolific oil seepage over a vast
region and in waters to
3000m+ centred on Green
Canyon
8. Seepage-slicks in Green Canyon are readily
observed and sampled at sea; don’t be confused,
this is oil, but is totally natural
This could be a picture over the Macondo spill!
It is the same oil!
9. There are thousands and thousands of natural
oil, asphalt vents, methane hydrate mounds
like these in the Santa Barbara Channel and in
the Gulf of Mexico
10. Seepage-slicks over Green Canyon
• Dense repeating and persistent seepage
• Exceptionally long slicks (some over 100km) especially
where strong surface current
• Characteristically ultra-thin (ship-wakes intersect them)
• Originate from many vents; not always possible to match
individual slick to originating vent
• Emission points often vertically above vents!
• Variation of seepage rate; seepage is periodic or blocked
by gas hydrates (oil and gas occur as hydrate below ~300m;
they can disassociate violently and present a major drilling hazard)
11. Why such prolific seepage?
• There is a widespread effective oil source
• There is volume of liquid oil (of course!)
• There is active multi-charging, migration/re-migration
• Salt diapirism forces oil upwards
• High overburden pressure resulting from kms
of sediment*
• Intense seepage of Green Canyon corresponds to
the juxtaposition of thick overburden and salt
*The same pressure that can overcome blow out
preventers and result in disasters like Macondo
12. Dense seepage and blow-outs go together
• Dense high rates of seepage results in part from high
overburden pressure
• High overburden pressure increases the risk of well blow-outs
• Furthermore in deepwater, explosive dissociation of methane
and ethane hydrates adds to the risk
• We have mapped these high seepage rate regions:
Santa Barbara Channel, Green Canyon, Campeche, Southwest
Caspian, Angola, Niger Delta, Black Sea and others.
All these have had well blow-outs and exhale methane to the
atmosphere (methane has 20x the warming effect as CO2 but is 200 less
concentration so contributes 28% of warming that CO2 contributes)
13. How much oil naturally seeping from Gulf of Mexico?
Seepage is so widespread and persistent no
overall estimate has been computed
Our guess, based on the seepage-slicks we have
mapped is that it is leaking between 80000 to
800000 gallons per day
And it has been leaking probably at least three
million years!