OIL SEEPAGE: AN INCONVENIENT TRUTH(OR THE PERCEPTION OF RISK IN OIL

PRODUCTION)

DR GEOFF LAWRENCE, TREICO LIMITEDMAY 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.

Just 100km from Macondo, the Gulf of Mexico’s natural seepage-slicks are so dense and persistent, they are observed on 1km resolution MODIS

Oil is being squeezed out of the GoM’s sediment like a sponge

The liquid oil seepage of the Green Canyon region of the Gulf ofMexico is the densest and most persistent on the planet anddefinite seepage-slicks are readily observed on most cloud-freeremotely sensed images, because slick reflect in allwavelengths. Seepage-mapping criteria were developed overpersistent oil seepage here and in California’s Santa BarbaraChannel, using, for example, Landsat optical images. Thecluster of nested slicks in the Green Canyon region on theMODIS image is distinctive. Satellite synthetic aperture radar(SAR) images have fine resolution and penetrate night andcloud to image slicks consistently at low to moderate sea state.

Green Canyon is a cauldron of seeping oil

5

Gulf of Mexico deepwater oil slicks

Green, red and pink are natural seepage-slicks mapped on satellite SAR. Dense repeating seepage coincide with many fields

2.

3.

1.

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

Natural tar mats

Prolific oil seepage over a vast region and in waters to 3000m+ centred on Green Canyon

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!

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

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)

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

Dense seepage and blow-outs go together

• Dense high rates of seepage results in part from highoverburden pressure

• High overburden pressure increases the risk of well blow-outs

• Furthermore in deepwater, explosive dissociation of methaneand ethane hydrates adds to the risk

• We have mapped these high seepage rate regions:Santa Barbara Channel, Green Canyon, Campeche, SouthwestCaspian, 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)

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!