4Km is *deep;*
A lot of this sort of stuff has been done around the 3000 ft mark in Texas for tapping heat from played out oil wells.
It's strange that they are not initially focusing on the areas around the big cities.
does the extraction efficiency vary *so* much that the transport losses from 2000 km are outweighed by the increased energy recovery?
Possible I suppose but hard to believe.
A very impressive feat of both IT and engineering if they pull it off.