Microbial Co2 Sequestration: from Coal-Fired Power Plants and Back to Coal
Coal-fired power plants in the United States are responsible for some 40% of the anthropogenic carbon dioxide (CO2) in the atmosphere. Several methods for geological CO2 sequestration have been suggested, including: injection into sandstone reservoirs, adsorption on coal, and reaction with serpentinite. We propose different approach, one that involves microbes within coal beds being used for sequestering CO2 captured from power plants. This approach has the additional economic benefit of enhancing recovery of coalbed natural gas (CBNG).
Our studies in the Powder River Basin (PRB), Wyoming and Montana, indicate that CBNG is biogenic in origin, resulting from methanogenic processes that generate natural gas in subbituminous coal beds. This conclusion is based on methane δ13C and δD isotopes, which indicate that methanogenesis is dominantly due to microbial reduction of CO2 and also results in part from microbial methyl-type fermentation. There is an indication that microbes in coal beds and associated pore waters are presently active or in stasis, and these in situ bacteria can be stimulated when appropriate chemical nutrients are delivered to the coal beds.
The proposed new approach to sequester CO2 in coal beds would involve, in addition to capturing CO2 in combustion gases (for example, by amine scrubbing), the injection of CO2, along with nutrients or chemical additives into nearby deep uneconomical coal beds for sequestration. This would initiate a methanogenic pathway of CO2 reduction by microbes consuming hydrogen (derived from water and coal) and a conversion of CO2 and organic acids to gain energy by generating methane, with water as a by-product of the biochemical reaction.
There are seven coal-fired power plants within 100 miles of the PRB that emitted 48.7 million tons of CO2 in 2007. If this emitted CO2 had been captured and injected into subbituminous coals not yet amenable to mining, and then sequestered by microbial CO2 reduction, 800 billion cubic feet (BCF) of new methane may have been produced in the PRB. During this same process, the CO2 could have displaced previously unrecoverable methane within the coal. With this secondary recovery, amounting to approximately 20% of the original CBNG resource, an additional 86 BCF of gas would be produced. The combined total of 886 BCF is more than twice the 2007 production of CBNG (430 BCF), with indigenous microbes the primary ingredient in sustaining this resource in the PRB!
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009