AltaRock Energy Melts Rock with Millimeter Waves for Geothermal Wells (2020)

Re:AltaRock Energy Melts Rock with Millimeter Waves for Geot... by mNovak on Thursday October 13, 2022 @11:03PM (#33199169)

As an RF engineer, this is a very creative application of mmW and I hope can be successful, but is not without very significant challenges which the company has made no claims to have solved. The issue is, mm-waves (and all high frequency RF really) are very sensitive to distance and losses. As a random example [1] gives some numbers for theoretical and precision machined waveguides in these frequencies. In the very best case we're talking about 0.03dB/cm loss. That means in the first meter of ideal waveguide you've lost half the power! And not just disappeared, you just dumped 0.5MW into the pipe itself, meaning it would likely melt within minutes. Meanwhile, their concept is to bore 20km into the earth.

The only way I could imagine this working is to lower the gyrotron itself down the borehole, but there's presumably tradeoffs of physical dimensions and output power that make it challenging. Again maybe not impossible, but there's no indication they've made fundamental advances in miniaturizing the source, or producing lossless waveguide.

Related, another interesting company I came across is Petra [2], who is doing something similar -- plasma/heat based non-contact drilling. But because they fracture the rock instead of vaporizing it, there's essentially gravel/sand leftover which is hard to evacuate from a deep vertical shaft, hence their focus on power/fiber trenches not geothermal.

[1] https://www.nrao.edu/meetings/isstt/papers/2012/2012151153.p...

[2] https://petra.cc/

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Re:AltaRock Energy Melts Rock with Millimeter Waves for Geot... by richk449 on Friday October 14, 2022 @12:35AM (#33199667)

For distance transmission at these frequencies, quasi optical systems are usually used. As you rightly point out, TE10 mode waveguide would be completely impractical.

See here for a good explanation of quasi optical transmission: https://www.bridge12.com/learn/what-are-quasi-optics/

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Re:AltaRock Energy Melts Rock with Millimeter Waves for Geot... by 1letterunixname on Friday October 14, 2022 @12:55AM (#33199789)

I'm thinking about the opportunity cost and the longevity of a solid-state rock, exo-"microwave oven" vs. drill bits.

How is it going to displace molten rock after it is softened?

And, if it's too hot for drill bits, how is it any better for electronics, power conducting cables, and cooling apparatus?

It seems like hammer technology in search of nails like flying cars and battleship rail guns.

One thing I do know is conventional microwaves heat the bejesus out of the edges of silicon dioxide objects like glass containers and ceramic bowls far sooner and better than they do food. Perhaps they have a dipole moment similar enough to water that it's unavoidable and typically enclose tasty vittles from spilling and sloshing all over.

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Re:AltaRock Energy Melts Rock with Millimeter Waves for Geot... by skagenpilot on Friday October 14, 2022 @06:25AM (#33201676)

> But because they fracture the rock instead of vaporizing it, there's essentially gravel/sand leftover which is hard to evacuate from a deep vertical shaft, hence their focus on power/fiber trenches not geothermal.

Getting cuttings out of the borehole is a solved problem with present drilling technics used in the Oil & Gas industry or geothermal. The drilling fluidsbrings them back. One needs the drilling fluids (mud) to avoid the well to collapse, I guess Petra is staying clear of deep borehole drilling because they can't operate their technology with drilling mud present. Also the deeper you go, the smaller the hole and they may face miniaturizion issues too.

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