Comment by anakaine | Hacker News Reader

Comment by anakaine | Hacker News Reader

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Former exploration geologist here.

Drilling that deep is not easy. Directional drilling equipment is very expensive, and heat + pressure take a toll very quickly on such equipment. Directionality is important as boreholes are rarely straight an it is entirely possible to drill a borehole in a U shape accidentally. Drilling requires high pressure pumps to clear the face of the drill bit, and the cut material must be returned out of hole. That's one hell of a compressor or mud pump. Below a certain depth rock behaviour changes from brittle deformation toward more plastic (and explosive) deformation, to eventually plastic deformation entirely. Groundwater pressures can collapse holes. Deformation can collapse holes. The rock grinds back at drilling gear. Equipment can become stuck and difficult to dislodge. Holes eventually collapse and partially close on their own, requiring casing of the hole. To case, drill a section, retrieve gear from down hole, slide casing in, replace Drilling gear, repeat for each length of casing. It can be quite different per hole, and per rig setup. Some rig setups permit casing in place (this is more a drillers specialist area than my own).

Then, there's the issue of keeping the hole open long term. Hydrothermal activity tends to dissolve minerals in water. Minerals tend to crystallise out inside boreholes and pipes over time, like hard water in water pipes in rural areas, constricting flow.

What is being proposed is difficult and requires an extreme amount of maintenance through its life cycle.

While all that is true the original article concerns using high intensity microwaves to drill, with an unbalanced purge gas. One of the advantages of this is the potential to create a glass casement as you drill. I'm not in the industry but it's a neat paper and your comment reads like you're simply unfamiliar with what they're proposing, ambitious as it is.

That’s because what they are proposing is untried fantasy at this point, and he’s talking about proven field reality.

MIT has verified the basics concepts at lower power levels. So while there's still uncertainty and risk here, it's wrong to say it's totally untested. It's trying to make the jump from lab demonstration to commercial viability, which is exactly what you'd expect a research project like this to be doing.

There is a vast difference between ‘verified at low power levels in theory’ and ‘bore hole maser drilling to multiple miles below the earth’.

The jump from lab demonstration to commercial viability is exactly the place where almost every tech trick fails.

So there is no need to pay this thing any attention. Geothermal under ideal conditions is not competitive. Steam turbines have operating costs solar and wind do not.

This is the same reason nukes are a dead end, and D-T fusion besides. It doesn't matter how cheap your heat source is if you need to pay for operating a steam turbine to get any power out. Solar and wind provide high-grade energy directly, so are impossible to compete with anywhere they work.

There are uses for direct heat piped underground to heat buildings, but you don't need to bore to 10km, or even 3km, to get enough heat for that.

To a lay person why do you mean by brittle deformation and plastic sand explosive deformation

When something hard is under pressure, it can bend or deform, or it can break or shatter.

Imagine a hammer striking a sheet of metal and the metal denting. For a brief moment, the pressure and heat of the hammer strike causes the metal to deform. Conversely, if the hammer hit something like a sheet of glass, it would shatter.

Plastic in this sense is not like Tupperware plastic at room temperature, but plastic heated when it is first being molded into shape.

Explosive deformation is again like the hammer hitting a sheet of glass- if the glass were already under pressure, breaking it would relieve the pressure causing shards to fly everywhere.

Rock at the surface is relatively cold and under little pressure- it is hard, but brittle, and simply breaks. As you get deeper, it is under more pressure and as it breaks, that pressure can get relieved unpredictably (fault lines cause formerly stable walls of already drilled hole to collapse).

With even more depth comes more pressure but also more heat, which relaxes the crystalline structure of the rock. It can start deforming rather than breaking. Drill bits become less effective as the rock flows around it rather than getting broken up and pumped away.

Edit: if you haven't watched videos of hydrologic presses destroying things on YouTube, you see something like this in reverse; sometimes things can deform a bit, but eventually explode under pressure. The most surprising to be to watch was a deck of playing cards literally shatter.

Dave Letterman did a whole series of crushing things with a hydraulic press. Quite entertaining.

> requires an extreme amount of maintenance through its life cycle

Precisely. Calling a plumber to plug a leak or remove a clog 10 miles underground is astronomically expensive.

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