Carbon storage capacity: there's plenty, but fracking may be wrecking some

[n2doc]

By Scott K. Johnson

Recent changes in the Earth's climate are primarily being driven by the burning of fossil fuels—that is, taking carbon from deep in the Earth, and dumping it into the atmosphere at breakneck speed. Wouldn’t it be nice if we could just sort of… put it back?

That’s roughly the idea behind carbon capture and sequestration (CCS). Carbon dioxide is captured from the effluent of a large generator, like a coal power plant, and compressed into a supercritical liquid. That liquid is then transported via pipeline to an injection station where it’s pumped deep underground.

But the technique requires some very specific rock formations if we expect the carbon to stay there. Two new studies have looked at how much CO2 we could hope to store, and how that storage may be affected by another process that's booming: fracking.

CCS can use the same rock configurations that sometimes host oil and natural gas. Like oil and natural gas, compressed liquid CO2 is less dense than water, so you need a geological cap that will prevent it from bubbling upward. That cap rock needs to be impermeable to flow (shale often fits the bill). If there’s permeable reservoir rock below that cap—like a sandstone—then you’re in business. Eight hundred meters below the surface, the pressure is sufficient to keep the CO2 in its compressed liquid state, and the reservoir rock will hold your fluid and the cap rock will keep it from escaping.

more
http://arstechnica.com/science/news/2012/05/new-estimate-of-potential-carbon-storage-capacity-theres-plenty.ars