It rises one concern on my end: what type of ground do we have to have in order to deploy such technique in an effective manner? Iceland is pretty much a volcanic pillar, basalt and similar stone layers seem great at preventing both escape and being inert to carbonic acid (H2CO3 that results in dissolving CO2 in water). Would it make any calcium-based (it reacts with CO2 and carbonic acid alike, Ca(OH)2 is even an indicator of CO2 in chemistry) sedimentary rock ill-suited for use? I have a vague hunch that under such pressure as presented in article it might look completely different, but it does pose some questions.
Anyone here knows a thing or two about geology and/or chemistry to answer that?