Saturday, June 19, 2010

And All The Kings Men... (Part 1 and a half)

posted by Armadillo Joe
Unexpectedly, I got some hits from my post yesterday about the Gulf disaster. One of them was a link from over at Political Carnival and it drove some traffic (and hence scrutiny) that I wasn't expecting with my quick and dirty original post. The whole episode over the last 12 hours has revealed to me that I wasn't as careful as I ought to have been and I want to make some clarifications here before I proceed with the rest of my case about why the American public and our leaders should all be much more concerned than they currently appear to be.
Two things:
1. I am not a petroleum expert, a geologist, an engineer or scientist. I am a guy who took some geology classes in college for his science credit, who reads a lot now, and who has enough of an understanding of the principles involved to roughly follow the discourse when the big brains start hashing out the particulars of this catastrophe. Anyone who links to the posts I'll be continuing over the next several days should understand that I am what you could consider a knowledgeable layman -- definitely not any manner of expert -- trying to broaden his own understanding of what is happening so that it can better inform his conclusions, and then sharing to the best of his ability those conclusions.
2. The items getting the biggest reaction yesterday were #3 and #4, not surprisingly. They were the most Hollywood disaster-movie apocalyptic. Allow me to clarify a little on each:
#3 - the Blow Out Preventer (BOP) dropping into the reservoir.
Not impossible, but very nearly so. I mischaracterized what could happen to the BOP, flat out. The oil reservoir is not a nougaty chamber of oily goodness with a thin crust of rock over it, through which the BOP could punch a hole like a spoon cracking the chocolate shell on a scoop of ice cream and sinking like a car crashing through the ice on a frozen lake.

The oil is in a pocket of sand (or a layer of sandstone) between layers of rock miles below the seabed and the most that could plausibly happen is that the compromised rock surrounding the bore hole, which is eroding fast as sand-saturated oil blasts & scrapes away at its structural integrity, would subside under pressure from the extremely heavy BOP (450 tons) resting on it in a point-load and also deflecting the concrete connection to the seabed to the breaking point by swaying in the ocean currents because the BOP is not only heavy, but also tall (see the picture). All that weight concentrates down to a single point at the bottom and the height makes it something of a sail and subject to lateral pressure from ocean currents. Should the surrounding seabed fail, the result would be a jagged column of broken rock with bits of BOP and drilling equipment stacked up inside it while oil squeezes up through the jumbled mess under pressure.
In other words, the image of the BOP crashing through the sea floor and fading into blackness in a lake of undersea oil like Leo DiCaprio at the end of Titanic is incorrect and I was wrong to leave that impression.
#4 - the oil "tsunami" -
Again, the word choice is rather poor. No 20-foot high black wave of oil is going to wash ashore across the Gulf; that's Hollywood disaster-movie stuff and that isn't a credible threat. 
What is a credible threat -- even if it a remote one -- is the layer containing the oil (essentially sand) compressing just enough as the reservoir pressure drops and the miles of rock above the sand layer that exert the very same pressure that turns any opening into a gusher continue to press downward even as the oil escapes and internal pressure drops. If it drops too far, the layers of rock can subside; afterall, the oil and sand compressed in place was enough to hold layers of rock apart.
In normal drilling situations, drilling fluid or "mud" is used not only to exert downward pressure in the drill string to control the upward flow of oil under pressure into the line, but also to maintain pressure in the reservoir and ensure that oil can continue to flow out. This is what pumping oil means. It isn't sucked out like you drink a milkshake through a straw; heavy fluid is pumped in to maintain pressure so the oil will come out on its own. Even the most productive reservoirs only give up about 50% of their available oil before equilibrium makes the necessary pressure too great for any man-made pumping machinery.
Thus, from my layman's rudimentary understanding of geology and drilling technology, it seems the relief wells being drilled in the area serve not only the purpose of lowering the pressure on the runaway gusher so it can be capped (by hitting the original bore from the side and giving the oil some other place to go besides a column of broken rock open to the sea above), but also to give the route for drilling mud to be pumped in to maintain reservoir pressure.
I don't know what kind of rock contains the oil and what manner of rock formation surrounds it. Most times something called lithostatic pressure (essentially, how tightly woven the rock is at a molecular level) holds the whole magilla together and prevents collapse. Also, collapses are more commonly associated with gas drilling because outright explosions and not the mere weight of the strata over a reservoir collapse the rock. And this well had been subject to quite a number of gas pockets. One such pocket may have been the catalyst for this whole calamity.
What I fear could happen, should the rock above subside (for whatever reason) and compress the reservoir layer, is that what is now a narrow column of broken and/or failing rock around the well bore could turn into a wide area of cracked rock as the dome subsides, through which the newly homeless oil will have no option but to suffuse and vent out, uncontrolled, in the form of leaks across a vast swath of the Gulf.
So, not so much a "tsunami" as a hemorrhaging. Again, not likely but not impossible. This guy thinks it might have already happened - Gulf Oil Spill Sea Floor Collapse and Seabed Leaks May Prevent BP From Capping Well.
So, again dear readers new and old, I apologize for the sloppy writing and hope this clears things up a bit.
More to come...

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