Just in case people aren’t aware of this, drilling wells the “old fashioned way” is a very advanced technology. Typically a mechanically complex diamond-tipped tungsten carbide drill bit grinds its way down, while a fluid with precisely calibrated density and reactivity is circulated down the center of the drill string and back up the annulus between the drill string and edges of the hole, sweeping the drill cuttings up the borehole to the surface. A well 4 miles long and 8 inches wide has a volume of over 200,000L, meaning that’s the volume of rock that has to be mechanically removed from the hole during drilling. So that’s the volume of rock you would have to “blow” out of the hole with compressed air. You can see why using a circulating liquid with a reasonably high viscosity is more efficient for this purpose.
The other important thing about drilling fluid is that its density is calibrated to push statically against the walls of the hole as it is being drilled, preventing it from collapsing inward and preventing existing subsurface fluids from gushing into the wellbore. If you tried to drill a hole with no drilling fluid, it would probably collapse, and if it didn’t collapse, it would fill with high pressure groundwater and/or oil and/or explosive natural gas, which would possibly gush straight to the surface and literally blow up your surface facilities. These are all things that would almost inevitably happen if you tried to drill a hole using microwaves and compressed air.
tl;dr, drilling with microwaves might sense if you’re in space drilling into an asteroid, but makes so no sense for this application.
Just in case people aren’t aware of this, drilling wells the “old fashioned way” is a very advanced technology. Typically a mechanically complex diamond-tipped tungsten carbide drill bit grinds its way down, while a fluid with precisely calibrated density and reactivity is circulated down the center of the drill string and back up the annulus between the drill string and edges of the hole, sweeping the drill cuttings up the borehole to the surface. A well 4 miles long and 8 inches wide has a volume of over 200,000L, meaning that’s the volume of rock that has to be mechanically removed from the hole during drilling. So that’s the volume of rock you would have to “blow” out of the hole with compressed air. You can see why using a circulating liquid with a reasonably high viscosity is more efficient for this purpose.
The other important thing about drilling fluid is that its density is calibrated to push statically against the walls of the hole as it is being drilled, preventing it from collapsing inward and preventing existing subsurface fluids from gushing into the wellbore. If you tried to drill a hole with no drilling fluid, it would probably collapse, and if it didn’t collapse, it would fill with high pressure groundwater and/or oil and/or explosive natural gas, which would possibly gush straight to the surface and literally blow up your surface facilities. These are all things that would almost inevitably happen if you tried to drill a hole using microwaves and compressed air.
tl;dr, drilling with microwaves might sense if you’re in space drilling into an asteroid, but makes so no sense for this application.
Also, polycrystalline diamond (PDC) bits are pretty common these days.