Coal deposits: Potential geological sink for sequestering carbon dioxide emissions from power plants

Unminable coal deposits may present an opportunity for the energy industry to sequester carbon dioxide (CO2) emissions from power plant stack gas. These coal (r)esources may be uneconomic for mining by being too thin, too deep, or too unsafe. In recent times, historically mined coals may also be too high in sulfur or ash content or too low in Btu value to be economically profitable. Unlike CO2-enhanced oil recovery where the CO2 is subsequently co-produced, injected CO2 into coals displaces the adsorbed methane (CH4) from the coal surface, two molecules of CO2 being trapped for every molecule of CH4 released. Proprietary industry field projects of CO2 injection into coalbeds have shown increased yields of produced CH4 over conventional coalbed methane (CH4) recovery. These coal deposits represent a widely dispersed potential geological sink for CO2 storage while at the same time offering an opportunity to recover commercial quantities of natural gas from coalbeds. The U.S. Department of Energy has been facilitating the evolving recognition and development of this novel CO2-CH4 concept in order to enhance coalbed methane production and evaluate a potential geological option for disposal of carbon dioxide from power plant stack gases.