[TangoLimaSierra]

The other problem I see is proppant mixing and transport with a -70 liquid. You need to keep the fractures open, too.

That's what I was wondering. Ya gotta have sand or rubber balls or something to move into the fractures. And something for them to flow in.

[no-s]

problem I see is proppant mixing and transport with a -70 liquid.

Pretty sure there exist conventional industrial processes that use liquid CO2 to transport particulates. Similarly for liquid nitrogen. If I'm reading the phase diagrams and such right those are supercritical fluids at those pressures and temps which means it will seep right into everything (no surface tension to speak of) and act as a solvent for all sorts of weird stuff (eg metal nanoparticles and polymers).

If you take the pressure off properly at temperature it can flash into vapor faster than the speed of sound in the rock, AKA earth-shattering kaboom. Unlike conventional explosives you can do this over and over again.

All in theory, of course. But it's not so "out there".