Friday, May 28, 2010
A rumor circulating in Louisiana's state capitol, Baton Rouge, has it that:
Secretary of the Navy Ray Mabus has reportedly floated the idea of sinking a battleship directly on top of the Macondo well in order to drop 80,000 tons on it and crush the drill pipe and the blowout preventer alike.
I proposed this idea on May 15th (using a barge) and submitted it to BP. BP says that it has received 17,000 suggestions to date, so mine is not necessarily unique.
Since proposing the idea, I have learned more about the geology of the oil-rich Gulf region. As I wrote on May 22nd:
On the other hand, a geologist with over 20 years in the oil industry tells me:
Does the Geology of the Spill Zone Make It Harder to Stop the Oil Spill?
We can't understand the big picture behind the Gulf oil spill unless we know the underwater geology of the seabed and the underlying rocks.
For example, if there is solid rock beneath the leaking pipes, with channels leading to various underground chambers, then it might be possible to seal the leaking risers and blowout preventer, with the oil flowing somewhere harmless under the floor of the ocean.
On the other hand, if there are hundreds of feet of sand or mud beneath the leaking pipes, then sealing the spill zone might not work, as the high-pressure oil flow (more than 2,000 pounds per square inch) might just shoot out into the water somewhere else.
We don't know the geology under the spill site. BP has never publicly released geological cross-sections of the seabed and underlying rock. BP's Initial Exploration Plan refers to "structure contour maps" and "geological cross sections", but all detailed geological information, maps and drawings have been designated "proprietary information" by BP, and have been kept under wraps.
However, Roger Anderson and Albert Boulanger of Columbia University's Lamont-Doherty Earth Observatory describe the basic geology of the oil-rich region of the Gulf:
Production in the deepwater province is centered in turbidite sands recently deposited from the Mississippi delta. Even more prolific rates have been recorded in the carbonates of Mexico, with the Golden Lane and Campeche reporting 100,000 barrel per day production from single wells. However, most of the deep and ultra-deepwater Gulf of Mexico is covered by the Sigsbee salt sheet that forms a large, near-surface “moonscape” culminating at the edge of the continental slope in an 800 meter high escarpment.
Salt is the dominant structural element of the ultra-deepwater Gulf of Mexico petroleum system. Large horizontal salt sheets, driven by the huge Plio-Pleistocene to Oligocene sediment dump of the Mississippi, Rio Grande and other Gulf Coast Rivers, dominate the slope to the Sigsbee escarpment. Salt movement is recorded by large, stepped, counter-regional growth faults and down-to-the-basin fault systems soling into evacuated salt surfaces. Horizontal velocities of salt movement to the south are in the several cm/year range, making this supposedly passive margin as tectonically active as most plate boundaries.
Porosities over 30 percent and permeabilities greater than one darcy in deepwater turbidite reservoirs have been commonly cited. Compaction and diagenesis of deepwater reservoir sands are minimal because of relatively recent and rapid sedimentation. Sands at almost 20,000 feet in the auger field (Garden Banks 426) still retain a porosity of 26% and a permeability of almost 350mdarcies. Pliocene and Pleistocene turbidite sands in the Green Canyon 205 field have reported porosities ranging from 28 to 32% with permeabilities between 400 mdarcies and 3 darcies. Connectivity in sheet sands and amalgamated sheet and channel sands is high for deepwater turbidite reservoirs and recovery efficiencies are in the 40-60% range.
See also this.
The BP oil spill leak is occurring in Block 252 of the "Macondo" Prospect in the Mississippi Canyon Area of the Gulf. The Mississippi Canyon Area is very typical of the Gulf oil region.
If the geology at Block 252 is like that described by Anderson and Boulanger for the Gulf oil region as a whole, then it might be difficult to stop the oil gusher without completing relief wells (which will take a couple of months). Again, if there are salt layers right under the sea floor, high porosity near the surface or salt movement, then sealing the leak by plugging the risers and blowout preventer might not work. The oil pressure is coming up at such high pressures that sealing the leaking equipment at the level of the seabed might just mean the oil will flow out somewhere else nearby.
The government must publicly release details of the geology under the spill site. The American people - and people in Mexico, Cuba and other countries which might be affected by the spill - have a right to know what we're dealing with.Until it does so, people will not have be understand what is going on. And failing to release such information may prevent creative scientists from around the world from coming up with a workable solution.
Macondo is not a sub-salt prospect. It's in between allochthonous salt bodies that have not formed a continuous canopy as exists further west. Also, obviously, it's a great reservoir, but it's middle or possibly lower Miocene in age, not Plio-Pleistocene.The bottom line is that I very strongly (and respectfully) suggest that the Secretary of the Navy - or anyone else considering these types of proposals - study the geological cross-sections and all other information regarding the geology beneath the seabed where the oil is leaking before deciding whether this idea will fix the problem or make things worse.
The near-surface sediment is young and unconsolidated muck. Shallow water-flow is a big issue here (that is overpressured unconsolidated sands, sometimes with biogenic gas or just overpressured brine -- a very unstable near-surface section.
For example, Rex argues:
The Gulf floor is soft sediments for hundreds or more feet down. If the pipe isn't tightly sealed by this process, the oil will be leaking into this sediment and start coming up all over the place.As I learned in geology class in college, you have to start with a solid understanding of the geology before figuring out how any action will affect the environment.
And for crying out loud, have a submarine check out this rumor to either debunk or confirm it.