Gulf Oil Leak: Explaining Pressure & Calculation

[Tregg Smith]

Can someone explain why with the tremendous pressure of- is it 5000 ft. of water-pushing down that oil can still leak out? I guess the oil pressure must be greater. How do you calculate the water pressure at that depth on the broken pipe. If the pipe is say one foot diameter would you figure a one foot column of water?

 

[future_think]

I am thinking since the water pressure is uniform the pressure isn't just pushing in 1 direction. Oil is lighter then water thus would exude a tendency to float. Also it is likely warmer then the water it is hitting.
The water pressure at the depth of 5000 ft is found by this formula found here. http://www.csgnetwork.com/h2odenscalc.htmlIs there a depth of water that you could submerge a surfboard in which it wouldn't return to the surface?

 

[russ_watters]

Water pressure us pushing down on the pipe but it is also pushing down on the oil reservoir so ultimately this pressure is irrelevant. Whatever additional pressure exists due to the gas buildup (I'm unclear on the specifics of that) is what causes the blowout.

Consider a balloon: with 14 PSI of pressure pushing in at the nozzle, how can the 0.5 psi or so of internal pressure cause air to escape?

 

[Bob S]

Is there a depth of water that you could submerge a surfboard in which it wouldn't return to the surface?

Yes. It will be crushed. and the buoyancy will depend on the buoyancy of the crushed components. Even nuclear submarines (USS Thresher) have been crushed by exceeding their designed depth.

Bob S

 

[mgb_phys]

Can someone explain why with the tremendous pressure of- is it 5000 ft. of water-pushing down that oil can still leak out?

The pressure in the oil reservoir is high enough that not only can it leak out - but when you actually drill into it the oil will reach the rig at the surface still with a lot of pressure. Oil rigs don't (generally) pump oil out of the reservoirs, it is squirted out by it's own enormous pressure.

Remember also in this case reservoir is under a couple of 1000ft of rock below the 5000ft deep sea bed - the oil is under much higher pressure than 5000fsw.

The pressure simply comes from the gas that has been created by the oil forming over millions of years being trapped under an impermeable rock layer. Sometimes the rock cap isn't quite impermeable enough and the gas escapes leaving the oil unpressurized. Generally for deep wells it isn't worth extracting in this case

 

[pallidin]

The pressure simply comes from the gas that has been created by the oil forming over millions of years being trapped under an impermeable rock layer.

Now THAT makes sense. I was wondering the same as the OP.

 

[xxChrisxx]

The pressure in the oil reservoir is high enough that not only can it leak out - but when you actually drill into it the oil will reach the rig at the surface still with a lot of pressure. Oil rigs don't (generally) pump oil out of the reservoirs, it is squirted out by it's own enormous pressure.

Sometimes the rock cap isn't quite impermeable enough and the gas escapes leaving the oil unpressurized

EDIT: Just realized you said this doesn't happen in all cases. Time for a quick rewrite :P

In the unpressurised cases artificial lift systems are used. Such as pumping down high pressure fluids, or using big electric pumps.

 

[RosieR]

I thought about this the other day and I just assumed that oil was slippery, so it would slip past the water thingies. Wow, I guess there is more to it.

Rosie.

 

[ruko]

Consider a balloon: with 14 PSI of pressure pushing in at the nozzle, how can the 0.5 psi or so of internal pressure cause air to escape?

Internal pressure mostly due to the elasticity of the balloon material.

 

[russ_watters]

Internal pressure mostly due to the elasticity of the balloon material.

I never said it wasn't!

...however, you do need to be more specific. While I know what you meant, it is also perfectly correct to say the internal pressure inside a balloon is mostly due to the atmosphere compressing the balloon.

I'm was being intentionally coy there and I'm doing it again here because I want people to realize there are two different ways of measuring/expressing the pressure.

 

[rcgldr]

Even if the oil pressure was lower that the water pressure before the drill opening was made, water would pore into the opening until the pressure was the same, then the oil, being lower density, and assuming it to be as nearly incompressable as water, would float upwards towards the water surface because of buoyancy.

 

[chiefsss]

Without having much information to go on, I was trying to come up with a solution to this problem...

Does anyone know how large the opening is and how thick the edge is on the pipe and what material it's made from? Is the top/opening smooth or irregular?

Just as a brainstorm idea, could they place a "super-strong" magnet on top of the opening (if they could get one a mile down)? or is the pressure too great? (again I don't have any info on this stuff with regard to the dimensions/quantities/forces/etc.)

 

[ruko]

I never said it wasn't!

...however, you do need to be more specific. While I know what you meant, it is also perfectly correct to say the internal pressure inside a balloon is mostly due to the atmosphere compressing the balloon.

I'm was being intentionally coy there and I'm doing it again here because I want people to realize there are two different ways of measuring/expressing the pressure.

I just attempted to answer your question. I did not infer you said anything! I think it is not perfectly correct to say that the pressure that forces air out of a balloon is mostly due to ambient air pressure compressing the balloon. I think a combination of both with the much larger edge going to balloon material memory. But I could be wrong.

 

[chiefsss]

...not the pipe itself, but the top of the BOP - if it was thick enough (enough magnetic surface area to create a good enough strong magnetic bond), could they use a huge super-magnet to cap it at the BOP (after cutting off the damaged pipe)?

 

[mgb_phys]

Even if the oil pressure was lower that the water pressure before the drill opening was made, water would pore into the opening until the pressure was the same, then the oil, being lower density, and assuming it to be as nearly incompressable as water, would float upwards towards the water surface because of buoyancy.

Normally the oil isn't in a big void like an underground tank. It's diffused through the rock - like water in quicksand. The big difficultly is often to get the oil out of the rock.

 

[mikeph]

Surely the pressures of the two liquids will quickly equalise if they are in contact, and the less dense liquid (oil) will rise. The shapes of the pipes or anything shouldn't affect the hydrostatics...?

 

[russ_watters]

I think it is not perfectly correct to say that the pressure that forces air out of a balloon is mostly due to ambient air pressure compressing the balloon.

I didn't say the ambient air pressure is what forces air out of the balloon, I just said most of the pressure in the balloon is due to ambient air pressure. I see this isn't making any sense to you, so I'll explain further:

--Atmospheric pressure is 14.7 psi.
--The pressure generated by the elastic of the balloon may be around 0.5 psi.
--Total pressure inside the balloon: 14.7+.5=15.2psi.
--Fraction of the air pressure inside the balloon due to atmospheric pressure: 14.7/15.2=97%
--Pressure trying to push air in the throat of the balloon: 14.7psi
--Pressure trying to push air out the throat of the balloon: 15.2psi

 

[russ_watters]

Surely the pressures of the two liquids will quickly equalise if they are in contact, and the less dense liquid (oil) will rise. The shapes of the pipes or anything shouldn't affect the hydrostatics...?

The pressure equalizes as the oil accelerates through the orifice. The delta-P between inside and outside determines the speed the oil travels through the orifice and the size of the orifice times the speed equals the flow rate.

 

[mcgiiver]

5000 ft x 65 lbs/ ft^3 / 144 = 2257 psi due to weight of sea water, Well pressure must be higher than that to cause flow.

 

[stewartcs]

...not the pipe itself, but the top of the BOP - if it was thick enough (enough magnetic surface area to create a good enough strong magnetic bond), could they use a huge super-magnet to cap it at the BOP (after cutting off the damaged pipe)?

The BOP has an 18-3/4" diameter bore.

CS

 

[Delboyrfc1976]

Can someone explain why with the tremendous pressure of- is it 5000 ft. of water-pushing down that oil can still leak out? I guess the oil pressure must be greater. How do you calculate the water pressure at that depth on the broken pipe. If the pipe is say one foot diameter would you figure a one foot column of water?

It would be very difficult to work out the pressure is at 5000 ft of water as you need to have know the mass of water. Here's a little what’s known in the industry as well control information for you.

Pressure of water in not pushing down on the oil it's pushing down on the sea bed and the drilling riser the leak is coming from the riser. When drilling a oil well a fluid called drilling mud is used it has several functions which are to prevent the well bore collapsing, to help cool and lubricate the drill string, to clean the hole when drilling but probably the most important to prevent a gas influx entering the well bore. Drilling mud in the industry is referred to as the first barrier what this means is when drilling the bottom hole pressure which is the pressure from the formation pushing upwards when drilling needs to be over come by the volume of fluid pushing down this prevents the dangerous fluids (H2S gas) entering the well bore. It is called the hydrostatic pressure it can be calculated using several formulas depending on operator’s instructions but here is one way to work it out

PPG (mud weight) * FT(current TVD Depth) *.052(constant) = PSI

Now if this is less than the pressure generated by the formation then the mud weight needs to be increased to prevent potential influx into the well bore i.e. a gas kick.

when drilling for oil encountering gas is a common thing but sometimes when drilling through formations you can drill into a gas high pressure pocket and if you imagine a balloon filled with water and you sick a hollow tooth pick in the size the pressure in the balloon is so great that it empties out from inside the tooth pick well the same thing happens when drilling into a gas pocket. I can go on all night I hope you get a better idea from my answer if you want more information let me know.

 

[Delboyrfc1976]

Can someone explain why with the tremendous pressure of- is it 5000 ft. of water-pushing down that oil can still leak out? I guess the oil pressure must be greater. How do you calculate the water pressure at that depth on the broken pipe. If the pipe is say one foot diameter would you figure a one foot column of water?

The pressure is nothing to do with the delta what ever. It is coming from the oil reservoir 20000ft or so below the sea bed the reservoir can produce pressures you would believe the problem BP have is how to cap this pressure and kill the well to stop it producing oil. like i say it the formation pressure releasing from the oil Reservoir.

 

[stewartcs]

It would be very difficult to work out the pressure is at 5000 ft of water as you need to have know the mass of water.

The mass of the water is not needed. The water pressure is extremely simple to work out. In fact, you have already given the formula below. All that is needed is the density and water depth to determine the pressure. So for 5000-ft of seawater the pressure is 0.052 x 8.56 ppg x 5000 ft = 2225.6 psi.

Pressure of water in not pushing down on the oil it's pushing down on the sea bed and the drilling riser the leak is coming from the riser.

The water is actually pushing down on the reservoir. It's just on top of the Earth instead of directly on the reservoir. The pore pressure in a normally pressured formation is dependent on hydrostatic head of the fluid from the surface to the point of interest in the reservoir.

CS

 

[dacarls]

Who can do this Physics calculation? Is it possible to pump liquid nitrogen through an insulated pipe past 1 mile of water to the bottom of the Gulf of Mexico, then down the now short riser, into the leaking oil well riser? If so, how far down into the well would the liquid N2 have to be pumped to gradually FREEZE the escaping oil and gas in the existing pipe?

This is the job that conventional drilling mud could NOT do when it was pumped into the top of the well with a huge leak blowing it out the top at the same time. Now there is apparently a large hole of some unknown shape where the 21 inch riser was cut off poorly. Is it possible to get a LN2 tube down past the BOP? (Blow Out Preventer, Hahaha), and deep enough to begin freezing the oil in place? This could give enough resistance to begin putting cement into the well.

 

[pallidin]

Who can do this Physics calculation? Is it possible to pump liquid nitrogen through an insulated pipe past 1 mile of water to the bottom of the Gulf of Mexico, then down the now short riser, into the leaking oil well riser? If so, how far down into the well would the liquid N2 have to be pumped to gradually FREEZE the escaping oil and gas in the existing pipe?

.

Would not work at all, but keep thinking.

 

[dacarls]

Would not work at all, but keep thinking.

Palladin: I see a statement of your opinion. Why not?

 

[cyber stealth]

How about attaching a device to the end of a narrow rocket and send the rocket down the 20" pipe to the bottom end of the pipe and let the device attach itself to the deepest end of the pipe, e.g., by opening an upside down metal unbrella so that the pressure of the gas and oil forces the device against the bottom end of the pipe, the more pressure the better the seal?

If the the pipe has a number of holes in the side of the pipe to let gas/oil in, the device could have arms it puts through the first holes it encounters, to lock itself into the pipe, instead of attaching itself to the end of the pipe.

The rocket would need to sense it's speed and not go over a few miles per hour, so that it does not damage the wall of pipe.

If there is no oxygen in the gas/oil in the pipe, I assume the rocket could not cause the oil/gas to burn.

 

[pallidin]

There would be too much risk of an unintended explosion using a 'rocket'

However, if one could insert, say, a hollow, 10-foot long, 3-inch diameter pipe that has 3-5 expanding non-corrosive bladders sectioned-off it might be possible to restrict the flow enough to properly cap.

 

[cyber stealth]

If there is no oxygen in the methane gas and oil in the pipe, how could the rocket flames cause the oil/gas to burn or explode?

 

[russ_watters]

It exploded at the surface, after mixing with air.