By injecting CO2 into basalt:http://www.ldeo.columbia.edu/news-events/turning-co2-stone-0
This is a really neat idea...I just enjoy the irony that environmentalists may have to embrace the notion that injecting chemical laden water at high pressure to fracture rock might actually be ok.
They used CO2 captured at the power plant, and mixed it with water and hydrogen sulfide, creating soda-like carbonation, then injected the mixture into porous basalt rocks 400 to 800 meters underground. Basalt, which is created as lava cools, contains calcium, iron, and magnesium, which react naturally with CO2 to form solid carbonate minerals.
I wouldn't think basalt to be very porous, but I guess it could be...just not very permeable.