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Today's Dialogue at the Oil Drum really gets into why 100,000psi is not the psi in the formation...

*************************************EXCERPT*************************************

I have spent the past 30 min looking for a good ref for over burden the source of the well's borehole pressure and haven't located one.

A good rule of thumb is .45 psi per foot of depth for sea water column and .75 psi per foot for rock formation.

The oil/gas zone is permeable, that means there can be no differential pressure between 2 points in the permeable zone except for the differential depth. So yes it's like a tire, except when it's flowing, pore size changes flow rates within the formation but not greater than the initial pressure.

Believe rock he has good explanation.

We need to put this 100,000 psi nonsense to rest. It makes TOD look less than reliable for facts.

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ROCKMAN on July 3, 2010 - 1:02pm Permalink | Subthread | Parent | Parent subthread | Comments top

Chip -- Dig thru the doc and you'll find a pressure plot. From the log data they estimate the OBG (overburden gradient) to be around 16 - 16.3 ppg. They probably used the wire line density log to come up with a site specific OBG. You'll also notice the frac gradient is in the upper 15’s. I suspect the low FG is why they’re setting csg just above the intersect: cut down the possibility of lost circulation.

ppg.http://energycommerce.house.gov/documents/20100614/BP-Production.Casing.TA.Options-Liner.Preferred.Long.Version.pdf

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geek7 on July 3, 2010 - 1:29pm Permalink | Subthread | Parent | Parent subthread | Comments top

I think one doesn't need a good reference to come to a conclusion that 100,000 psi is VERY suspect. Here is what I did:

To have a high pressure there must be a great weight of overburden. I convert psi to lb per cubic foot. I know that 5000 ft of column is H2O and that the remaining 13000 ft are something else. I propose a two layer model x feet of shale (because shale is a very common geologic deposit in places where people drill for oil, density 167 lb/cuft) and y feet of gold (because its density is high, 1204 lb/cuft). I then have two equations in two unknowns:

(100000 psi)*(144lb/sqft/psi)-(5000ft*62.4lb/cuft) = 1204 * x + 167 * y
and
13000ft = x + y

I solve for x and y and get:
y (thickness of shale) = 1508 ft
x (thickness of gold) = 11,492 ft

Anything less dense than gold does not have a solution. (And there is nothing on Earth more dense than gold.)

So, to believe that 100,000 psi number, one has to believe that BP drillers are so focused on finding oil that they ignored 11000 ft of strange shiny metal in the mud returns. IMHO, there is something really wrong about this model. Maybe, just maybe, 100000psi is simply wrong.

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WebHubbleTelescope on July 3, 2010 - 1:57pm Permalink | Subthread | Parent | Parent subthread | Comments top

That's a beauty of an analysis. Sticking gold in the equation is genius as it both gives you a solution and points to its preposterousness.

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manofmetal on July 3, 2010 - 2:05pm Permalink | Subthread | Parent | Parent subthread | Comments top

Did you pick up any of your knowledge building a dam on the Arkansas river in the 1970's.

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wrb on July 3, 2010 - 2:11pm Permalink | Subthread | Parent | Parent subthread | Comments top

So the NWO is keeping the gold secret?

Probably plan to flood the market as soon as everyone has converted their savings to gold.

Dastards.

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lotus on July 3, 2010 - 2:13pm Permalink | Subthread | Parent | Parent subthread | Comments top

Dang it, boy! Oh, my poor drowned keyboard.

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sunnnv on July 3, 2010 - 3:02pm Permalink | Subthread | Parent | Parent subthread | Comments top

(And there is nothing on Earth more dense than gold.)

http://en.wikipedia.org/wiki/Density#Densities_of_various_materials

Ummm - what about Platinum, Iridium and Osmium?

One might say "Gold is one of the most dense metals/elements known".

Au 19,250 kg/m^3
Os 22,610 kg/m^3 - 17 % more dense.

Otherwise - a good analogy, thanks for QUANTIFYING things with real numbers.

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motownmutt on July 3, 2010 - 7:39pm Permalink | Subthread | Parent | Parent subthread | Comments top

(And there is nothing on Earth more dense than gold.)

'ceptin': 19.32 g/cc Gold Au 79
19.35 g/cc Tungsten W 74
19.84 g/cc Plutonium Pu 94
20.2 g/cc Neptunium Np 93
21.04 g/cc Rhenium Re 75
21.45 g/cc Platinum Pt 78
22.4 g/cc Iridium Ir 77
22.6 g/cc Osmium Os 76

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manofmetal on July 3, 2010 - 1:37pm Permalink | Subthread | Parent | Parent subthread | Comments top

You are concerned that the Gas pressure in the hole could be up to 100,000 psi. So lets look at the reasonableness of that concern.

Using some simple verifiable facts for a basis of our investigations we can say these things are true and unchangeable:

A cubic foot of water weights 62.4 pounds and has a specific gravity of 1

A cubic foot of limestone has a specific gravity of 2.7 times that of water so it weighs 168.48 pounds.

The well is about 13000 feet below the sea floor that is 5000 feet below the surface or about 18k feet total.

Lets take this step by step:

To estimate total psi of the overburden we can say;

If we stack 5000 cubic feet of water at 62.4 pounds per cubic foot, one on top of the other for 5000 vertical feet we get 312,000 pounds per square foot.
There are 12 inches by 12 inches of area at the bottom of the column so there is 144 sq inches upon which 312,000 pounds rests so we divide and get 2167 psi.

If there is 13,000 feet of limestone that weighs 168.47 pounds per cubic foot and stack that up we get 2,190,240 pounds per sq ft or 15210 pounds per sq inch of overburden.

So we end up with a weight on the formation of 15210 psi and 2167 psi or 17377 psi total weight over the production formation.

So if the weight of the formation is 17K psi and the gas pressure is 11k psi then we are very likely safe assuming that the rock is not holding back gas produced in an area of higher pressure. Logically 17 thousand pounds will hold down 11 thousand pounds.

The rub comes when we look at the totals in a very rough way. There is nearly a pound of pressure per foot if the depth is 18k and the pressure is 17k. Therefore if gas is formed at a depth of 100,000 feet and migrates upward we would be in store for 100ksi pressures that would be held back by a 17k weight. I think we all agree that it is not likely that 17k can hold down 100k of pressure over any geologic time frame, even without the drilling of a well. Therefore any high pressure gas would have leaked out years ago and it is likely that the drill log is right in saying the pressure is in the 11k range. But it is not impossible that gas formed about 20 miles down. And it is possible that it did migrate into the production zone. But it would be a miracle if it stayed there for even a short period of time.

Disclaimer: This is based on very rough numbers and violates rules of thumb that indicate the overburden pressure could be a few hundred pounds less.

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joemichaels on July 3, 2010 - 1:51pm Permalink | Subthread | Parent | Parent subthread | Comments top

Thanks to Manofmetal, Rockman and geek.

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jimvj on July 3, 2010 - 2:27pm Permalink | Subthread | Parent | Parent subthread | Comments top

The above analyses assume that the pressure of the oil in the pocket is entirely due to the weight of the overburden. Is it ever the case that, in addition to overburden, there is pressure due to gas production in the pocket that would pressurize it even more?

The gas production could be due from conversion of liquid oil to gaseous methane, or oxidation to CO2, or even to chemical processes unrelated to the oil.

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ROCKMAN on July 3, 2010 - 3:43pm Permalink | Subthread | Parent | Parent subthread | Comments top

Jim -- That actually is one of the sources of “abnormal” pressure. Normal (or hydrostatic) pressure in the GOM is essentially the pressure from a salt water column at that depth. But “geopressure” develops from of a number of causes. NG generation as one source. Another is actually simpler: is the sediments are compressed during burial and if there are no conduits for the water to be “squeezed” out of the rock the pressure will increase above hydrostatic. This typically occurs when sandstone reservoirs are entirely encased in impermeable shales. That appears to the at least one source of the geopressure in the BP reservoir.

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PaulS on July 3, 2010 - 3:54pm Permalink | Subthread | Parent | Parent subthread | Comments top

There's surely some sort of a limit on how much it can be overpressured beyond what gravity would suggest - after all the shear and tensile strengths of rock are not infinite. So something would fail somehow, and the oil/gas would find its way to the surface...

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MEpatriot on July 3, 2010 - 4:01pm Permalink | Subthread | Parent | Parent subthread | Comments top

How strong is 13,000 vertical feet of rock?

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aflaliz on July 3, 2010 - 5:29pm Permalink | Subthread | Parent | Parent subthread | Comments top

If I understand correctly, the fracture pressure in the Halliburton document's Table 1.11 cited above helps to answer your question. If the pressures are greater than the fracture pressure, the rock fractures and the pressure is released. The estimated fracture pressures are all less than 15000 psi. That is why the 100,000 psi numbers are unbelievable. Those sort of pressures would have fractured the formation.

On a marginally related topic-- mostly out of curiousity -- has anyone run the numbers on how much the pressure should have dropped due to 30+ days of flow? I tried it out, and get a roughly 1000 psi drop, which seems rather high so I might have had an error. I assumed a high permeability-- 1 darcy, a 60 foot reservoir thickness, and 30000 barrels/day outflow.

Let me add this...from the Oil Drum:

Halliburton docs, for reference (see Table 1.11 for pressure stats): http://tinyurl.com/33zsg9f

I don't know the technical stuff about calculating the well pressure, but I know that it has to be above the water pressure a mile deep.

I have been wondering, how did the blowout preventer fail? Why is there no way to actuate a manual valve down there by a ROV?

It seems to me that the first requirement for this type of deepwater well would be to have redundant ways to shut it off.

But then, if they could shut it off, it might just blow the valve off the ocean floor and flow anyway.