I'd have to look it up...
...but as I recall the wells at the Rocky Mountain Arsenal were not intentionally fracked, but I could be mistaken. This was about the same time as Project Rusilon, where a well was fracked in western Colorado using a nuke, so anything is possible.
In order to get the CO2 down to 8000 feet, it will have to be under a pressure that is greater than the lithostatic pressure at that depth. It will enhance the pore pressure (the pressure of fluids in cracks and the spaces between grains) within the reservoir rock, reducing its fracture strength under differential stress.
We'll find out for sure when they start pumping.