Microbial Co₂ Sequestration: from Coal-Fired Power Plants and Back to Coal

Stricker, Gary D.¹; Flores, Romeo M.¹; Spear, Brianne D.^1
1 MS 939, US Geological Survey, Denver, CO.

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