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July 19, 2010
Steven Chu's Snake Oil
You probably have been hearing a lot of nonsense lately about the integrity of BP's Macondo well casing. A lot of it has been coming from those who ought to know better, specifically including Energy Secretary Chu. Click here for a copy of the well diagram saved from the DOE website. I recommend that you print it out to follow along. What we will look at is on the left hand side of the page.
Starting at the top it says "ML @ 5067'MD/TVD". Translating, it means Mud Line @ 5,067' Measured Depth/Total Vertical Depth.
Next it says "16" supplemental adapter @ 5227' in 22" extension joint 18".375" ID (1.25" wall pipe above" - That is the "hanger" for the 16" casing. Just below the hanger, if you look at the wall itself, you will see a dark vertical line on the outside (the 36" casing), a gray band (cement), another dark vertical line (the 28" casing), more cement, a third dark line (the 22" casing), a white space (the annulus between the 22" and 16" casings), another black line which is the 16" casing and then another white space with the number "14" which is the annulus between the 16" casing and the 9-7/8" production casing which is shown filled with blue (sea water).
Next is the bottom of the 36" casing at 5,312' MD/TVD (254' bml [below mud line])
Now we get to the first of Dr Chu's screwups, the "16" rupture/burst disk sub". .We will return to the subject of rupture disks shortly.
Next it says "TOC @ - 5067' MD/TVD (mudline)" which means the Top Of Cement is at the mud line. The bottom of that cement job is shown next at "28" @ 6217' MD/TVD (1150' bml)". So the 28" casing is cemented all the way along its length from 5067' down to 6217'.
Next comes a reference to the internal drill pipe (567' MD - Bot of 5-1/2" 21.9 ppf S-135 (3450' of pipe")) which we can ignore because it has nothing to do with the integrity of the casing.
Next is another "TOC 2 - 5067' MD/TVD (mudline) indicating that the 22" casing is also cemented all the way up to the mud line. So if the casing were to fail at the surface around the Blowout Preventer (BOP), it would have to rupture through three thicknesses of casing (36", 28" & 22"), plus the two layers of cement. And if it were more than 160 feet below the mud line (5227 - 5067 =160) you can add the 16" casing too. Relax Dear Readers, the well is intact near the mud line.
Now please note that the 16" casing goes all the way down to 11,585', a distance of 6518' below the mud line and is cemented up to about 10,500 feet. Therefore, it has over 1000 feet of cement between its lower end and the rough well bore.
The production casing is described on the right side of the page near the bottom "7' 32# x 9-7/8" 62.8). Deciphered that means the lower part of the production casing, which goes down to 18,114.93' MD, is 7 inches in diameter and weighs 32 pounds per foot. It transitions ("XOVER" AKA crossover) to a 9-7/8" diameter, 62.8 pounds per foot pipe at 12,487.64'.
Now let us come back to the rupture disks. You'll see there are three shown at 6047', 6304' and 9560'. They are all shown as 16" disks. You may ask how does Dr Chu get 16" rupture disks into a 9-7/8" production casing? OOOOPS. Actually, the rupture disks are very small and are placed in threaded holes through the collars that are used to screw sections of 16"casing together. I do not know the manufacturer of the disks, but since I sell rupture disks in my day job, I'll use some of my manufacturer's literature to explain what is going on.
Here is the link. Given that it is installed using a "1/4" hex bit socket" it is a very small device. It is screwed into the collar from the ouside so that the flow is directed inward. As noted above, there is drilling mud between the 16" casing and the casings outside it. That mud is in contact with the surrounding rock which varies in temperature from 48 degrees F at 5,312 feet to 262 degrees F at 18,360 feet. As the ground heats the mud it will expand. If it expands too much, it will create a pressure on the outside of the 16" casing trying to implode the 16" casing. So the rupture disks are intended to provide thermal relief of that annular space around the 16" casing. The casing is under more threat of implosion than explosion.
So Dear AT Readers, don't believe the government when they try to sell you Doctor Chu's Snake Oil that the well lacks pressure integrity above 11,153 feet total vertical depth. In fact the most likely place where the well has failed is through the cement shoe between the "Top Float Collar 18,11.93 MD" the "7" Shoe @ 18,303.92' MD".
BTW - I see that the New York Times has re-written its puff piece on Dr Chu from last Saturday to delete this passage:
That's right Dear Readers. If Dr Chu had kept his mouth shut, BP's top kill probably would have succeeded and the damn hole would have been plugged by Memorial Day. More oil may have fouled the Gulf of Mexico because of Steven Chu than because of BP!