I have a question for the scientifically-minded?

[kentuck]

Regarding oil wells under the ocean:

If you put a pipe into the earth below 5000 feet of water, would it exert more pressure than a 1' foot pipe at the bottom of the ocean? Taking into account the water pressure from 5000' above? Which would bring the most oil out of the ground??

:-)

[tekisui]

1. I am not sure there would be a difference.

However, right now, there is a big kink in the pipe, like a garden hose, the leak is lessened. The kink is deteriorating, if it goes, the leak rate would go from 210,000 gallons/day to 4.2 million gallons/day.

[kentuck]

2. Would not the water pressure at 5000 feet have any impact

on the flow of oil out of the ground? Seems like that would be a lot of downward pressure??

[tekisui]

4. I don't think so. But, I'll await word from someone who remembers physics better than I.

[TransitJohn]

6. The hydrostatic head pressure of the water column above the wellhead

is miniscule compared to the pressure in the pore spaces of rock underneath 30,000 feet of other rock. That's why the oil is migrating upwards towards the water. Think of elementary fluid dynamics, fluids migrate from high pressure zones to low pressure zones.

[kentuck]

7. One would think we would see more natural oil "spills"?

if the water pressure above did not have a critical impact on what was below the earth??

[jberryhill]

22. Under the water - there is more rock

And, as demonstrated by, say the existence of Hawaii or Iceland, the water doesn't keep the rock down.

[zeemike]

8. The oil is much deeper than 5000'

they go down another mile or two into the rock....and so the oil is under more pressure than it would be at 5000'
And once the oil is in the water it will come to the surface because it is lighter than the watter. and will continue until the oil is exhausted.

[TransitJohn]

9. The deepest deepwater GOM wells are going 25,000 to 30,000 feet into the rock.

I think this one was 18,000ft. More than one or two miles.

[kentuck]

11. Right, but..

...the water is only 5000' deep. What would happen, for example, if the pipe was cut off at the ocean floor? Would the water pressure from above slow the oil pressure from below?

[jberryhill]

25. No

Not by a longshot.

The pressure exerted at the bottom of a mile of water is NOTHING compared to the pressure where this oil is coming from - under two miles of rock.

Rock beats more than just scissors

[kentuck]

29. If you say so....

As I noted, I am no scientist.

[FarCenter]

12. Water pressure at 5000 feet is a little over a ton per square inch

About 2165 psi IIRC.

If the crude oil has a specific gravity of 0.82 (and different crudes have varying spedific gravities) then the pressure at the bottom of a 5000' pipe filled with crude would be 0.82 x 2165 or 1775 psi.

Suppose however that the oil is at the bottom of a hole 8000 feet below sea level under 3000 more feet of rock with a specific gravity of 2.5. Now the total pressure of sea water plus rock overburden at the bottom of the hole could be:
2165 + (3/5)*2.5*2165 = 5412 PSI

However, the oil in the 8000 foot well would have a pressure of 8/5 * 1775 = 2840 PSI.

So there is a pressure differential of up to 5412 - 2840 = 2572 PSI available to push the oil up the well. Hence the blowout.

Now the above is not exact, since the pressure of the oil flowing out of the sand at the bottom of the well is not as much as the simple calculation would suggest, given that the rock is stiff and there is resistance to flow through the sand or rock to reach the well.

But that is the general idea.

During drilling, the well is supposed to be filled with a dense "drilling mud" in order to overcome the pressure of the oil under the weight of the rock.

[BeFree]

14. Pressure under the rock?

Not necessarily so. There are caverns in rock that are not pressurized... at least on land. Just because there is sea pressure, doesn't mean there is pressure being exerted on the oil therein.

I think....

[FarCenter]

15. Oil and gass reservoirs are under domes of relatively impervious rock layers

For example, the reservoir may be under a dome of salt. Salt is fairly plastic, so if there are thousands of feet of rock above a dome of quite a large diameter, which have had millions of years to deform and settle downward, the pressure could be a good fraction of what I calculated.

Note also that per TransitJohn, this well was much deeper than 8000 feet below sea level. So the pressures in the reservoir would be much greater.

[kentuck]

16. I imagine the pressure underground is what causes the oil to shoot...

out of the ground in geysers? But if a steel pipe is put down into the ocean, the pressure from below would fill that pipe a certain distance or it would geyser out the top. But the pressure inside the steel pipe would not be the same as on the outside. Therefore the top of the pipe, at the top of the water, would exert less pressure on the oil than would a pipe only one foot off the ocean floor. Uh, nevermind. :-)

[BeFree]

24. I do know this

In some oil wells water is injected to force the oil up and out.

Surely there are oil pools under pressure. Just as surely there are pools of oil not under pressure.

Drilling down 10,000 feet must at times bring some surprises as to what pressure the oil is under.

At the top of the pipe the air pressure is 14.7 psi. So if the pressure of the oil is above that it will rise up and out of the pipe. If the psi of the oil is at say 1,000 psi, you got your geyser.

[TransitJohn]

26. Hydrocarbons don't exist in 'pools'. They're in pore spaces.

Yes, secondary recovery with water flushing is sometimes performed on older oilfields, because the water will fill up pore space, and because of the hydrophobic nature of alkanes (alkanes are nonpolar, water is one of the most polar molecules), the hydrocarbons are forced up the reservoir. However, mechanical action is still needed to pump the petroleum out. Think of all the pumpjacks you've seen. Drilling down 10,000 feet doesn't bring many surprises in the way of pressures (that's all planned out and everyone's briefed in pre-spud and daily meetings), but can bring much in the way of surprises with structural geology. Especially if no seismic has been shot in the area.

[BeFree]

37. So

As the rock squeezes the oil (compresses with a live load) the rock collapses?

[TransitJohn]

19. With respect, you don't know what you are talking about.

Yes, the overburden always exerts pressure on any fluids contained within the pore space of rock. Hydrocarbon fluids do not exist in 'caverns'. Highly compressed fluids are necessarily under pressure.

[BeFree]

28. So, every well is free flowing?

Of course not.

Not every pocket of liquid underground is under pressure.

There are deep caverns that have overburden and there is no pressure in them other than atmospheric pressure. Think of these oil pockets (some of them) as we think of aquifers. Just because we stick a straw in those aquifers doesn't mean the water comes geysering up.

[TransitJohn]

31. Yeah, what do I know?

I'm just a petroleum geologist working a rig 17 miles from the site of the Deepwater Horizon. Thanks for putting me in my place. Fuck I hate DU sometimes.

[BeFree]

33. Just answer the questions then

Is every well a free flowing well? And if it is free flowing (some are, some are not) how long will it flow freely?

[Earth_First]

3. Do you have a link for those numbers, tekisui?

[tekisui]

5. Yeah, I should have put it in:

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=389x8259678

[kentuck]

10. delete

wrong response

[BeFree]

13. Pressure differences

When there are pressure differences that become uncontained, pressure will seek equalization.

The water pressure at 5,000 feet is _________? Lets say 500 pounds per square inch. PSI

The oil pressure in the rock is ___________? Lets say 0 psi.

If so, the water will force it's way into the space the oil occupies until the pressure is equal. 500 psi.

The displacement of the oil will have to take place and the only place to go is up the well hole. And since oil floats on water it is just a matter of time before almost all of the oil in the pocket leaves the pocket and enters the Gulf.

I think....

[Rex]

17. I've read that there could be billons of barrels of oil, coming out of

3 leak areas, wonder how long that takes?

[kentuck]

18. I would think it possible...

that the pressure from above, especially 5000 feet of water pressure, could force the oil back down into the earth, conversely.

[TransitJohn]

23. 30,000 feet of rock exerts a hell of a lot more pressure on the oil than 5000 feet of water.

As noted above. :hi:

[kentuck]

27. How do we know there is 30,000 feet of rock?

And why don't we have more "natural" spills from the pressure below the earth??

[TransitJohn]

30. Right, 18,000 feet at this well I think.

And there are many natural spills of oil, they're called seeps.

Edit: spelling :dunce:

[jberryhill]

38. Because we drilled through it to get at the oil

18000 in this case, but, really, it's no mystery how much rock is over an oil deposit because when you reach oil, you know you're there.

[BeFree]

32. Eh?

Is that a live load or a dead load?

[jberryhill]

20. The water pressure is nothing compared to the pressure of the rock

Oil deposits are typically like a highly compressed sponge underneath a layer of nonpermeable rock. The pressure comes from the rock which, as you can imagine, is a lot heavier than a mile of water.

[BeFree]

35. So

Is the rock exerting a live load upon the oil?

[happyslug]

21. Oil fields are the the result of a cap over the oil

A well drills THROUGH that cap. Now if the well has some sort of pressure (Other oil or more likely Natural Gas) then the oil will force it way through the hole made by the drill. As the well ages you may have to pump the oil up but does NOT seem to be the case in this blow out.

Also remember oil floats on water so if any oil goes through the drill hole, it will float to the surface. Thus the problem is the drill hole itself and it needs to be capped.

[BeFree]

34. Oil way underground

Depending on several factors, it may be vaporizing and creating pressure all on it's own?

And, if the rock is producing pressure then how did the oil force its way into the rock?

[TransitJohn]

36. Try reading.

http://en.wikipedia.org/wiki/Petroleum_geology

[BeFree]

39. Interesting

"Gas generation starts at similar temperatures, but may continue up beyond this range, perhaps as high as 200°C."

As gas is generated (from the oil?) it wants to occupy more space. If space is limited (confined) it will create pressure.

You read all that, I presume, did you understand it, too?

[happyslug]

46. At about 20,000 feet the heat of the earth turns oil into Natural Gas

Remember solids take up less space then liquids, Liquids less space then gases. As the oil converts to natural gas, the oil changes from a liquid state to a gaseous state. This change in the state of the oil/Natural gas builds up pressure under the oil dome (cap) for Gas takes up a huge amount of space compared to a liquid, even of the same material. When we drill into such an oil dome, the oil is under pressure from the natural gas to go and up the drill hole it will go, pushed by the Natural gas elsewhere in field. Sooner or later the Pressure disappears and you have to start pumping the oil out, but that can be years from now (and pump in water to drive the oil to the pump to be pumped out, but that is a Secondary recovery method, not a factor at the present time).

This conversion from oil to natural gas (which includes an conversion from liquid to gaseous state) provides most of the pressure in most oil wells. When no natural gas is present, it is rare to have a gusher, but common in wells with a high percentage of natural gas in the underlying oil field being drilled. We do NOT hear of gusher to much any more do to the fact in most such fields we can guess how much natural gas is in the field and to prepare to handle such a gusher, but most wells today tend to be into non-gaseous wells i.e. no pressure so they have to pump from day one instead of waiting for the pressure to drop before pumping. The big worries today for gushers are these deep wells, i.e. around 20,000 feet deep. If the well is 100$ natural gas all you have is a huge fireball as the gas leaks into the air before it is capped, if it is 100$ oil, you have to start to pump from day one no gushed (This is what happened to Colonel Drake when he did the first oil well in 1859, it was 100% oil and he had to pump it out).

The problem is fields with BOTH natural gas and oil, those occur up to about 20,000 feet deep. Now natural gas can occur without being converted from oil, thus you can have natural gas in well that has oil, but you get more of such mixed wells as you drill around 20,000 feet.

For you information, the US could drill to 20,000 feet in 1938, the 50,000 deep wells you hear of today are natural gas only wells. For this reason we have a rough idea of how much oil is in the world today, for such information could be found by 1938 (Through actual research would take to the 1960s), we have a lesser idea of how much natural gas exist today, we have a rough idea but it is considered less accurate the the rough idea of how much oil exists.

One last comment, not only can pressure build up in the field do to the conversion from oil to Natural Gas, the earth itself can bring gravity on the field via the rocks. If the pressure in the field is high enough it can stop this downward pressure but such pressure itself will re-start once the pressure inside the field has dropped (do to the oil being pumped out). This is a minor source of pressure compared to the conversion of Oil to Natural gas but it is still a factor. There are other causes for a pressure build up, but all are minor competed to the conversion from oil to natural gas (Or the conversion from plant matter to natural gas directly, which would be a conversion from a Solid state to a gaseous state).

[BeFree]

47. Downward pressure

How is this downward pressure measured?

An active pressure means something has to be moving in order for pressure to occur. Are rocks actually moving toward the core? Is the earth slowly getting smaller? Is the globe contracting into an ever smaller ball?

[happyslug]

48. Here some places to look for that information

Depth calculator at various oceans depths:
http://www.calctool.org/CALC/other/games/depth_press

Details on Depth and pressure:
http://www.engineersedge.com/fluid_flow/relationship_depth_pressure.htm
http://www.tpub.com/content/doe/h1012v3/css/h1012v3_25.htm

Details on the "Gas laws" i.e. the relationship between pressure, volume and Temperature:
http://en.wikipedia.org/wiki/Gas_laws

Temperature, on average, goes up 3 depress Celsius, for every 100 meters you go down into the earth (This varies from one area to another but becomes more stable the deeper you go:
http://www.energyquest.ca.gov/story/chapter11.html

Sub-surface temperatures in most of the world right under the surface is about the same as the average temperature in that area. For example where I live (Johnstown Pa) average temperature and sub-surface temperature is about 54 depress Fahrenheit. 300 feet deep it increases to 59 degree Fahrenheit, 600 feet 76 depress Fahrenheit etc. Most caves are less then 100 feet from the surface so tend to be about what ever the local average temperature is, but mines and wells that go deep tend to end up with 100 plus degree temperatures at the lowest depths where people operate (i.e. the Diamond and gold mines of South Africa). Oil and Natural gas wells go deeper with even higher temperatures. With increase temperatures you have increase volume of gas and increase pressure.

Now to a degree the above varies from location to location on the planet, but as you go deeper the more accurate is the above formula.

[kentuck]

40. Thanks to everyone for their very helpful responses...

Now I would ask whether or not the huge burning of oil on the sea creates clouds that could affect the weather and cause massive floods in Tennessee??

[BeFree]

41. Doubt it

But all that rain falling upstream of the Gulf, may just send a great plug of fresh water into the Gulf and help flush the oil into the Atlantic a little faster. We need it dispersed as quick as possible.

[jberryhill]

42. No

I'm guessing your regular occupation does not involve considering and comparing the relative proportions of things to one another.

Rain is caused by the precipitation of evaporated water in the air. Smoke does not cause rain.

Just what is it you think we were planning to do with all of that oil If there had been no leak - and indeed all of the oil that comes out of all of the oil wells everywhere?

[kentuck]

43. I suppose you were going to sell it and make billions of dollars...

if there had been no spill. But there was a spill.

I suppose you might work with the traders on Wall Street that work for Goldman Sachs and that speculate in oil futures to drive up the price to $4 per gallon to get back your money, no matter how much oil you pumped or spilled. Just my opinion.

[jberryhill]

44. I guess you missed my point

The oil was going to be burned.

It is what we do with oil, and I was trying to put into perspective the fact that we are burning a lot more oil than this every day. That might lead you to thinking that the relative climatic impact of burning this amount of oil would not be much in comparison to what is burned every day.

I don't see the connection to Goldman Sachs, but they didn't make it rain in TN either.

[kentuck]

45. I suppose the dark, dirty clouds of burning smoke...

could block out the sun and cause the temperature to drop, just as volcanoes do? So, yes, I think it could have a climatic impact. I don't know if it could change the weather patterns a great deal? But, it might. I'm superstitious. It's not nice to mess with Mother Nature.