Drilling into Earth

[All Seeing Eye]

If we built a huge drill and started drilling vertically into the Earth how deep could we potentially go? could we go as far down as the mantle in order to tap the heat for power?

 

[JustAFriend]

You don't need to go down to the mantle.

Lots of heat is already available much closer and easier to tap. Far easier to produce the power at location near geothermal activity and then run the power across the national or international grids from there.

Here's the world's deepest hole, 7.5 miles:
http://www.damninteresting.com/?p=567

 

[Jadzia]

At what point do we hit magma. Or does that just occur in pockets below fault lines around tectonic plates?

 

[PlixTixiplik]

The thickness of the lithosphere (the crust plus the rigid upper mantle) varies depending on where you are. Under mid-ocean ridges it can be as thin as 20 km, typical ocean lithosphere is 30-50 km, and continental lithosphere is 100-150 km thick.

-MEC

 

[anais]

The drill would melt a loooong time before it can hit any magma.

Geothermal heat pumps for private homes reach down a few hundred feet.

 

[All Seeing Eye]

Geothermal heat pumps for private homes reach down a few hundred feet.

So we can drill down 7.5 miles but a few hundred feet is adequate for heat pumps for homes?
When we build new homes why are we not drilling huge holes into the ground to tap into the heat for the houses? We'd have no more reason to need natural gas to warm our central heating.

 

[Verteron]

When we build new homes why are we not drilling huge holes into the ground to tap into the heat for the houses? We'd have no more reason to need natural gas to warm our central heating.

That's a great question.

The answers are that currently it's more expensive than buying fossil fuels (probably not over a long term but people rarely see the long term picture), and in many places, people aren't allowed to drill because they don't have the freehold to the land, or the freehold is restricted by whichever government governs the land to allow for utilities and mines under houses.

The deepest hole ever drilled was drilled by the Russians, article about that here, the Kola Superdeep Borehole.

However, it was only 7.5 miles, a mere scratch in the surface. At the bottom, temperatures hit a whopping 180°C (356°F)!

 

[anais]

Well I can't speak for we but here in Norway heat pumps have become common over the past decade. It is an investment, but perfectly doable for people with the money to buy a house and pays off in 5 years.

 

[All Seeing Eye]

Oil rigs in the North Sea are on the continental shelf where the Earth's crust is thin (less than 10 kilometres). I've heard that these oil rigs can (when the oil runs out) be converted into Geothermal power plants. They can drill into the Earth below the north sea and tap the geothermal power there.

I hope this turns out to be the case.

 

[Mr. B]

Oil rigs in the North Sea are on the continental shelf where the Earth's crust is thin (less than 10 kilometres). I've heard that these oil rigs can (when the oil runs out) be converted into Geothermal power plants. They can drill into the Earth below the north sea and tap the geothermal power there.

I hope this turns out to be the case.

Oil companies would probably be very interested in deriving additional revenue from those platforms considering their massive expense. I wonder how you'd transport the power fomr some of those great distances.

 

[All Seeing Eye]

Well I suppose if they connected all the platforms together by undersea cables and then had a single cable running to the mainland it would save money laying cables because there'd be less cable. But Geothermal would be a never ending supply, for as long as the Earth exists power could be tapped from the North Sea so the price of the cables would be irrelevant because the money to be gained from the geothermal power would easily pay for it. Of course power would be lost over the distances needed to travel but power should still reach the mainland in large enough quantities.

 

[Alpha_Geek]

At what point do we hit magma. Or does that just occur in pockets below fault lines around tectonic plates?

IIRC, just below the mohorovic(sp?) discontinuity... Been a looong time since Earth Science classes!

 

[Ariadne]

Geothermal heat pumps for private homes reach down a few hundred feet.

So we can drill down 7.5 miles but a few hundred feet is adequate for heat pumps for homes?
When we build new homes why are we not drilling huge holes into the ground to tap into the heat for the houses? We'd have no more reason to need natural gas to warm our central heating.

Well, mostly price. It's cost-effective with a reasonable pay-back period in some areas (Iceland, the areas of BC with lots of hot-springs, etc), and it's somewhat common there.

 

[trekkiedane]

Well I can't speak for we but here in Norway heat pumps have become common over the past decade. It is an investment, but perfectly doable for people with the money to buy a house and pays off in 5 years.

Those usually just concentrate heat from slightly below the lawn or from the atmosphere -and not geothermal heat (They're also increasingly popular here!)

 

[farmkid]

Well I suppose if they connected all the platforms together by undersea cables and then had a single cable running to the mainland it would save money laying cables because there'd be less cable. But Geothermal would be a never ending supply, for as long as the Earth exists power could be tapped from the North Sea so the price of the cables would be irrelevant because the money to be gained from the geothermal power would easily pay for it. Of course power would be lost over the distances needed to travel but power should still reach the mainland in large enough quantities.

I'm not sure a cable is the best way to do that. Aren't some of them several hundred miles from land? That's a long way to run a cable to carry that much electricity. Also, undersea cables are frequently cut by ship anchors or geological events, or other such stuff. Such damage to a cable carrying a large electric current could be very bad.

I think a better idea would be to use the energy on site to hydrolyze sea water to produce hydrogen, then transport the hydrogen to land. The hydrogen could then be used to produce electricity through combustion or in fuel cells.

 

[All Seeing Eye]

I think a better idea would be to use the energy on site to hydrolyze sea water to produce hydrogen, then transport the hydrogen to land. The hydrogen could then be used to produce electricity through combustion or in fuel cells.

You mean like THIS but with Geothermal energy.

I LIKE IT!

 

[Ariadne]

Well I suppose if they connected all the platforms together by undersea cables and then had a single cable running to the mainland it would save money laying cables because there'd be less cable. But Geothermal would be a never ending supply, for as long as the Earth exists power could be tapped from the North Sea so the price of the cables would be irrelevant because the money to be gained from the geothermal power would easily pay for it. Of course power would be lost over the distances needed to travel but power should still reach the mainland in large enough quantities.

I'm not sure a cable is the best way to do that. Aren't some of them several hundred miles from land? That's a long way to run a cable to carry that much electricity. Also, undersea cables are frequently cut by ship anchors or geological events, or other such stuff. Such damage to a cable carrying a large electric current could be very bad.

I think a better idea would be to use the energy on site to hydrolyze sea water to produce hydrogen, then transport the hydrogen to land. The hydrogen could then be used to produce electricity through combustion or in fuel cells.

Transporting hydrogen is not that easy either.

 

[trekkiedane]

Transporting hydrogen is not that easy either.

Well, that too is being dealt with:

In 2007 Dupont and others reported hydrogen-storage materials based on imidazolium ionic liquids. Simple alkyl(aryl)-3-methylimidazolium N-bis(trifluoromethanesulfonyl)imidate salts that possess very low vapour pressure, high density, and thermal stability and are not inflammable can add reversibly 6-12 hydrogen atoms in the presence of classical Pd/C or Ir0 nanoparticle catalysts and can be used as alternative materials for on-board hydrogen-storage devices. These salts can hold up to 30 g / L of hydrogen at atmospheric pressure, which is twice that compressed hydrogen gas can attain at 350 atm.

Emphasis mine
Wikipedia

 

[Dayton3]

The mantle is considerably denser than the crust.

And at the depths necessary to drill into the mantle, the rock acts more like a liquid (and I'm not talking about magma) and flows into any voids.