Geophysics Professor Mark Zoback explores the potential of unconventional natural gas (shale gas, coal bed methane and tight gas) sources replacing coal as a step in transitioning the US economy towards zero carbon. He briefly describes the three different varieties and how they are produced. During his description of coal bed methane he talks about how the methane found in coal seams is actually adsorbed on to the surface of the coal and in order to extract it, the methane needs to be desorbed off the coal by reducing the pressure. But another way is to actually pump CO2 down into the coal seam and as the carbon dioxide likes to adsorb to the coal surface more than the methane it can actually replace it. So the concept is pump down CO2 into coal bed methane wells and boost methane production. Just like EOR (Enhanced Oil Recovery) in oil reservoirs it could be a huge win-win scenario. The concept may also apply to shales as well.
Unconventional gas production as well as this type of Carbon sequestration is still in the very early days of study, but the potential could be very promising.
Update (Oct 2012) – found the link was dead and here is what I hope is the same or a very similar talk.