[Hyoi]

Pumping CO2 is one of the techniques for extracting oil from wells once considered dry.......TW

The gas used is mostly nitrogen, but you're correct in that injecting a formation, sometimes even with plain water, is a common technique and is called secondary recovery. And I wasn't seriously making light of the idea of CO2 injection, but I do think that extra measures should be taken to protect water formations. New casing, good cementing techniques, the good sense to P & A and redrill if the bond logs are poor, et cetera; particulary, and here's the real kicker with coal, if the gas has substantial hydrogen sulfide content. H2S is none other than a cast iron bitch to deal with.