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The flow out the top relieves the pressure inside the well. If you restrict the flow, there's more chance of (additional) structural failures below the restriction...
by asdf on Fri Jun 18th, 2010 at 12:47:20 AM EST
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How exactly a restriction redistributes the pressure? By how much?

And what do we know about the location of the present cracks?

by das monde on Fri Jun 18th, 2010 at 12:58:22 AM EST
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I don't know, but the story seems to be that the top kill approach was terminated because of concern about the internal integrity of the well...
by asdf on Fri Jun 18th, 2010 at 01:02:37 AM EST
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We know very little and, while we may be able to see where hydrocarbons seep (or gush, as the case may be) out of the sea floor, the structure of the layers of rock and sediment between the sea floor and the oil reservoir is likely only known through seismic data which is very coarse.

Data on drilling pressure and hopefully rock composition would have been collected as the well was being drilled, and that's also important.

By laying out pros and cons we risk inducing people to join the debate, and losing control of a process that only we fully understand. - Alan Greenspan

by Migeru (migeru at eurotrib dot com) on Fri Jun 18th, 2010 at 01:23:31 AM EST
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On page 8 of this file, a suspected "major loss event" is marked at the 18200 feet level, while the well bottom is at the 18360 feet (about 50 meters below). If we can get that far, a good try wood be to reach the bottom and spread a sieve (or plug) under there.

My thread at The Oil Drum is here.

by das monde on Fri Jun 18th, 2010 at 04:47:58 AM EST
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The BOP, when open, has the same internal diameter as the largest casing. Normally, everything passes through the BOP. It's pretty big, I would guess, repeat, guess, that it's on the order of about 75 cm in diameter.

Right now, though, since they already have activated (or tried to activate, or partially activated) the various annular and shear rams, it's tough to say what is going on inside. Probably there are several very irregularly shaped restrictions through which the oil is flowing. They could take off the BOP, at which point the drill string would probably blow out (several km of steel rod flying through the air), and the flow would increase because of the reduced restriction...

by asdf on Fri Jun 18th, 2010 at 09:59:43 AM EST
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by asdf on Fri Jun 18th, 2010 at 10:02:25 AM EST
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On page 8 of this file,...

"This file" is for Macondo, which they abandoned, I believe. That event should have been a wake-up call. I do not know if the two wells are in the same formation.

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Fri Jun 18th, 2010 at 04:04:55 PM EST
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I do not know if the two wells are in the same formation.
 

Yes, they are.  

And, yes, it should have been (a wake-up call, that is).  

But the failure of the first well put them behind schedule, which is why they rushed the second well and cut so many corners drilling it.  MBA management is idiot management.  They are like our incompetent winter drivers who drive faster on snow and ice--and leave less margin for errors--because, !of course! the bad weather has made them late.  

The Fates are kind.

by Gaianne on Sat Jun 19th, 2010 at 03:52:23 PM EST
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the structure of the layers of rock and sediment between the sea floor and the oil reservoir is likely only known through seismic data which is very coarse.

I saw a report on NBC Nightly News that the first relief well was within 2,000 feet of the bottom of the original well bore. If the illustration was to scale it would appear that it is much closer to the well bore horizontally. They noted that progress had to slow because of the dangers of the proximity to the original bore. The relief bore appeared to be approaching tangential to the well bore, perhaps less than 200 meters from the original bore. At a very minimum they should have the well cores from the relief wells as additional data points on the characteristics of the rock from the floor of the Gulf down to the oil reservoir.

The density of TNT is given as 1.55g/cm3. The well bore is about 0.5 meters. Let us assume that it would be possible to place an explosive charge of 0.25m dia. at the bottom of that bore and that the charge is 10 meters long. The cross-section of the explosive would be 0.049 sq. meters. At 10 meters length  the volume would be 0.0.49m3 or 4.9x108 cubic centimeters. 1.55g/cm3x4.9x105 cubic centimeters = 4.9x105 grams or 4.9x10<SUP2</SUP> kilograms, or about 50kg of TNT. Even if it is possible to place an explosive charge of .4m diameter and 10 meters length that would only be 1.256 x 105 ccs and 1.256x1.55 x 10 grams or 1.95 x 102 kg, or about 200kg of TNT. (Assuming no math errors!)

Having little knowledge of explosives I still have my doubts that this is sufficient to compress >100 meters of rock sufficiently to crush the well casing and the drill pipe, whereas a fractional kiloton nuke likely would. But, perhaps they are drilling two wells so as to be able to attempt a "bottom kill" of the well with cement or some higher density special cement while having the first relief well available to perform explosive compression if needed.

At the current depth of the first relief well there is over 10,000 feet of some kind of rock above it and it is only another 2000 feet to the reservoir. It is certainly not inconceivable that the well could be collapsed sideways without producing a collapse to the surface.

"It is not necessary to have hope in order to persevere."

by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Sat Jun 19th, 2010 at 07:03:41 PM EST
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Your math's a bit off.

Your cross section area is correct, at 0.049 m2. Call it 1/20th of a square meter. A ten meter charge makes it half a cubic meter. At 1.55 T/m3, that gives you three quarters of a ton of TNT, or 750 kg, to play with.

With a .4 m diameter, you get the next best thing to two tons of TNT. That's still a couple of orders of magnitude from a kT, of course...

- Jake

Friends come and go. Enemies accumulate.

by JakeS (JangoSierra 'at' gmail 'dot' com) on Sat Jun 19th, 2010 at 07:18:31 PM EST
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(nearly) of the relief well with chemical explosives.  So I would be creating a line source for the explosion rather than  a point source.  I would be seeking to crush the gusher along most of its length, rather than just at one point.  The impact from the explosion would fall off with distance, rather than distance squared, which should enhance its effect.  

Alternatively, by choosing a sequence of detonation times, the explosion could be focused to highten the effect at one point in the gusher column.  

And following your calculation, the energy would then approach the kiloton range.  

That doesn't mean it would work, though.  

The Fates are kind.

by Gaianne on Sat Jun 19th, 2010 at 07:57:25 PM EST
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I don't know what the temperatures are at those depths and pressures. The Russians had to cool the bore before they inserted the nuke. Above a certain temperature TNT becomes unstable, I believe. Cooling and then inserting a large quantity of TNT might be problematical. I should stick to qualitative analysis. :-)

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Sat Jun 19th, 2010 at 09:50:24 PM EST
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I dropped a decimal place at the same place I screwed up the script for my exponent. The exponent was a 2 and I only moved the decimal point one space. That was after finding a three order of magnitude error that gave a totally unbelievable result! I'm terrible.

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Sun Jun 20th, 2010 at 12:49:54 AM EST
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