Question about oil wells and pressure.

[Ayahuasca]

This BP well is about 5,000 feet down, which means that the water pressure keeping the oil in is TONS per square inch, so the pressure pushing the oil out must be much, much greater, so where does that pressure come from?

Any if the pressure is so great, why aren't there any 'oil volcanoes'?

?

[Brother D]

Maybe at a guess, the billions of tons of water pressing down on top of the mantle at that point of the ocean? Oil/Gas is less dense than water/rock. No different than if you had a bottle of oil/air held under water then if you puncture the bottle you'd get a stream of air/oil coming out.

[HowMuchLonger]

Oil/gas is held down there by a "cap" rock. An impermeable layer that the oil/gas can not move through. The fluid has already migrated upwardsuntil it can not go any higher. The pressure of this is higher than that of the ocean bed. To hold the gas back whilst drilling the "mud" (drilling fluid used is weighted up to a much higher density so that the hydrostatic head is equal to that of the reservoir, in some cases caesium formate is used to increase the mud weight. If the mud weight is too high there is a damnger of fracturing the formation and losing all your mud. Bear in mind that reservoirs are drilled with either water based mud or oil based mud, the oil base can be very expensive, so you dont want to lose it (also this can be a logistical nightmare getting a continual supply of new mud).

Edited by HowMuchLonger on Friday 28th May 15:02

[thepawbroon]

It's the rock...called a trap.

The crude oil permeates upwards from the source rock until it is prevented from doing so by impermeable cap rock. Under this rock is where the reservoirs form. If the cap rock wasn't there, the oil would permeate almost unnoticably into the ocean.

[thepawbroon]

ha ha! too slow

[GTIR]

I thought they pumped gas into the well to pressurise it?

But then I always thought a book on my mums shelf at the family home said "Rogers Treasure" but actually said "Roget's Thesaurus" so what do I know!

[HowMuchLonger]

GTIR said:

I thought they pumped gas into the well to pressurise it?

But then I always thought a book on my mums shelf at the family home said "Rogers Treasure" but actually said "Roget's Thesaurus" so what do I know!

As the field gets older the reservoir depletes the pressure will also decrease. They can drill more wells into the same reservoir, then inject water at high pressure to force the remaining oil out.

Edited by HowMuchLonger on Friday 28th May 15:20

[69 coupe]

If the Earth fractures and moves continuously on its tectonic plates, surely there must be oil trapped at some of these locations either land or sea based.

Do we ever get Hugh natural gushers of oil/gas leaking into the sea or similarly on land?

[Parsnip]

Depends on the reservoir, but the drive usually comes from several sources:

Gas stored above the oil at huge pressure forces the oil out and up through the wellbore as it expands. There is also gas in solution which expands as the reservoir pressure drops, forcing out more oil - a lot of this gas will also reach the surface and will be re-injected to maintain reservoir pressure to increase the oil recovery. There is also water down there, which does not mix with the oil, providing a further source of drive.

These are natural drive mechanisms, but injection of fluids (water being a common one) to enhance oil recovery is becoming more common. Artificial lift mechanisms to get more oil out are also more common than they once were - basically anything to get more oil out faster.

[D_T_W]

It's also worth remebering that they don't drain the reservoir dry, there's anything up to 2/3 of it still left in the ground as they aren't smart enough to figure out how to drain it completely. They'll get there eventually, but it's going to take a while!!

[Oakey]

D_T_W said:

It's also worth remebering that they don't drain the reservoir dry, there's anything up to 2/3 of it still left in the ground as they aren't smart enough to figure out how to drain it completely. They'll get there eventually, but it's going to take a while!!

Can't they just use a big straw?!??


"I..... DRINK.... YOUR..... MILKSHAKE!!!!"

[HowMuchLonger]

Oakey said:

D_T_W said:

It's also worth remebering that they don't drain the reservoir dry, there's anything up to 2/3 of it still left in the ground as they aren't smart enough to figure out how to drain it completely. They'll get there eventually, but it's going to take a while!!

Can't they just use a big straw?!??


"I..... DRINK.... YOUR..... MILKSHAKE!!!!"

It is important to note that the oil&gas is not stored in a big cavern in the ground. It is actually in the pores of the rocks *bit like a solid sponge.

[GTIR]

HowMuchLonger said:

GTIR said:

I thought they pumped gas into the well to pressurise it?

But then I always thought a book on my mums shelf at the family home said "Rogers Treasure" but actually said "Roget's Thesaurus" so what do I know!

As the field gets older the reservoir depletes the pressure will also decrease. They can drill more wells into the same reservoir, then inject water at high pressure to force the remaining oil out.

Edited by HowMuchLonger on Friday 28th May 15:20

You've sent me to sleep......

[uk_vette]

Hi All,
Well there is a slighhtly new twist to the fact that some oil is still not available to the extraction process.

So the scientists have had a rethink,,,,,,

Instead of bringing the oil up, out of the ground to burn it, and release its energy, why not burn it in situ?

So there is moves a foot now to burn the oil in situ, inject oxygen and water into the caverns, and return the water in a heated state.

It sounds a bit far fetched, but to have an underground fire, for want of a better description, don't sound to bad an idea ?