Thanks. In principle I am wholeheartedly in support for geothermal as a renewable energy source, especially compared to fossil fuels. I think these kinds of developments to expand the potential for geothermal resources are super important.

I guess I just would like to understand some of the externalities to this particular methodology. Especially since many of the parallels to oil and gas fracking are present, and the environmental track record there is poor.

> I just would like to understand some of the externalities to this particular methodology

I would too. Their white paper devotes an entire section to induced seismicity. There is less attention paid to steady-state water requirements. (Given it's just water and brine, and assuming natural prop pants, the threat to the water table seems de minimus, barring something nasty dissolving out of the rocks.)

My reading of the comment above is that Geothermal uses the same chemical/physical process to fracture the rock and has to dispose of those chemicals afterwards (or leave them in place). Fossil fuel fracking needs a continuous supply of the chemicals and a continuous problem of finding a reservoir for the used chemicals so the impact is much, much higher.

The rate that geothermal energy replenishes is incredibly slow. Average heat flux through continental crust is around 70 milliWatts per square meter[0], so a single well with a horizontal drilling range of 3km would in steady state generate about 2 MW thermal, or around 0.8 MW of electricity. For comparison a single onshore windmill typically produces around 2 MW of electricity. As an example, to steady state power the state of Delaware, you'd need to completely frack 13% of the area of Delaware. You actually frack substantially less if you don't wait for the heat to regenerate, and you deplete an area bit by bit.[1]

[0] There are volcanic areas where the heat flux is substantially (~5-10x) higher, but they are few in number, generally far from population centers, and creating geologic instability in close proximity to a volcano carries its own risk. Viable in places like Iceland but not generally.

[1] Eventually of course you would wind up fracking the same total area, but it would take centuries to millenia, by which point you've probably either switched to a better power source or learned to deal with the issues of fracking.

IIRC (and I'm not an expert), you need to keep working on the cracks to keep water circulating. You don't need as much stimulation as you would for fracking since the goal isn't to crack new areas, but your well will stop working if you don't monitor and stimulate as needed.