by Lisdexamfeta on 6/3/24, 6:46 PM with 171 comments
by pfdietz on 6/3/24, 9:03 PM
Some schemes fracture the rock between two boreholes, but this requires fiddly positioning of the wells as well as the fractures. Another interesting approach is to increase the thermal conductivity of the rock around a single well. Much of the thermal resistance is in the rock close to the well (as can be seen by examining the relevant integral), so this doesn't have to affect too far out to have a significant effect.
A company XGS Energy recently raised $20 M in series "A" funding for this. Their fluid (which is forced into fractures around the borehole) is proprietary, but is thought to contain graphite dust. Graphite can be three orders of magnitude more thermally conductive than rock, so incorporating it into even narrow fractures can have a major effect.
https://news.ycombinator.com/item?id=40434975
https://jpt.spe.org/hot-rock-slurry-developer-of-emerging-ge...
(the field tests mentioned there must have been successful, as they raised that $20 M subsequently.)
Because this technology involves a single well that remains sealed from the surrounding formation, it could be used in existing played-out oil or gas wells, some of which go quite deep (although that's in basins with low geothermal gradients or else the fossil fuels would have been destroyed.)
by gzu on 6/3/24, 8:20 PM
by sfink on 6/3/24, 8:06 PM
Though maybe the tunnel liner part is too much of a stretch. It sounds like the vaporized rock wants to turn to ash. I don't know if there's a way of concentrating the once-solid parts and keeping it hot enough while routing it to the tunnel wall. It just seems like a cool set of problems to solve, resulting in a self-contained (minus the energy source) burrowing drill that can create arbitrarily long stone tunnels underneath (non-volcanic) land.
DIY lava tubes!
by krunck on 6/3/24, 7:38 PM
by api on 6/3/24, 8:01 PM
The Earth itself is a giant fission reactor and molten metal thermal battery, but for some reason nobody thinks about it.
This would be far easier than fusion or even next generation full cycle fission but it’s barely funded.
by peter_d_sherman on 6/4/24, 4:32 AM
Now, such a device would probably seem a little bit far fetched...
But the first step in making such a device, if it could ever be engineered, would be to melt the inserted raw earth into a hot liquid state. (From this hot liquid state further chemical refinement processes could be completed, such as scooping out heavier elements from the bottom and lighter elements from the top of the liquid. Any emitted gasses could be captured and cooled down, liquified, etc. From there further chemical refinement processes of the liquids could take place, ultimately resulting in refined Elements being output...)
This technology -- the ability to "melt rocks" (aka, the ability to melt raw earth, any raw earth notwithstanding its chemical composition) might just enable the taking of that first step to creating such a machine...
Such a machine, should it ever exist, would find great application on Mars in the future, should it ever be able to get there...
Anyway, I wish this company a lot of luck in their endeavors!
by drtgh on 6/3/24, 9:09 PM
From how such progressive temperature change (extraction) would affect the dynamics of the Earth's core, among other things, to how it would affect such temperature to the nature chemical processes on the surface, how it would affect vegetal life (cultives), and so on.
The planet is big, but we are talking about, lets say, a century of use or more. Has anyone calculated were would be the limit of holes (on geothermal a new hole each XX years due area cold down) before the "we never guessed that X could happen"?
by toss1 on 6/4/24, 4:50 PM
However, one issue with geothermal that I didn't see addressed is that iirc, geothermal systems start out great, but as water/fluid is pumped down and back up hot, minerals rapidly deposit themselves on the plumbing and decrease the system efficiency and ultimately kill it. Could this system be used to more quickly, cheaply, and regularly perform maintenance, or is this just one good step to get broad geothermal applications, and that remains a problem to be solved?
It's be great to hear from any experts in the field - thx!
by eluketronic on 6/3/24, 7:25 PM
Is there any existing +3km deep geothermal well energy system in use?
by goda90 on 6/3/24, 11:10 PM
Does anyone know how much of the atmosphere's heat comes from geothermal energy as opposed to solar radiation? By extracting geothermal energy we'd be increasing that effect in the short term, but would it even be significant?
by greenthrow on 6/3/24, 8:08 PM
by auspiv on 6/3/24, 7:29 PM
This is true. Neither the article nor the CEO of the microwave drill company say why.
At that depth, rock isn't a solid. It behaves plastically. The traditional tri-cone bit used could make progress, but it kind of just started "massaging" the rock. The bit (as all bits do) wore out. They pulled the drill string out of the hole to put a new bit on. The borehole would close back in during the multiple days it took to pull 40kft of drill string out, change the bit, and put it back in. Progress was not possible.
Unless the microwave drill includes some enormous cooling system (that works 40kft down hole even when the drillstring is removed!), they will face the same issues.
Also, separately, I saw pictures of the resulting lab-drilled hole on LinkedIn the other day. The hole shows a high rugosity (qualitative description of the roughness of a borehole wall). Similar photo here - https://spectrum.ieee.org/media-library/image-of-a-rock-surf.... That's a ugly hole, and would be very difficult to run casing into it.
Further - traditional well drillers' #1 focus is controlling pressure downhole (typically done by varying the density of the drilling mud). If the pressure becomes too great, a blowout can happen, which is bad news for everyone involved (see the BP Deepwater Horizon incident). For geothermal wells, they presumably will try to avoid hydrocarbons. However, rock far above water boiling point can cause a BLEVE (boiling liquid expanding vapor explosion), which is also undesirable. Super curious to see how they intend to control bottomhole pressure with statements like this - "Instead of pumping fluid and turning a drill, we’ll be burning and vaporizing rock and extracting gas, which is much easier to pump than mud."
