CO2 Sequestration Potential in Thin and Shallow Coal Beds: Eastern Kansas
Coals that are not attractive mining targets can be utilized for coalbed gas (CBM) production and CO2 sequestration. Eastern Kansas is underlain by several shallow (<1500 ft depth) and thin (1 to 4 ft) Pennsylvanian coals, which range in rank from high-volatile C to A bituminous. These coal beds can serve as sinks for large point-source emitters of CO2 because the number of beds at a given locality can have an aggregate thickness of several feet. These coals have the potential to produce CBM, and theoretically they can sequester approximately twice that volume in CO2. Gas content of the coals can be as great as 375 scf/ton (as-received), and the composite thickness of several coalbeds can improve economics for enhanced coal bed methane (ECBM) projects.
A study area underlying a metropolitan landfill in eastern Kansas investigated the CBM and ECBM potential for several underlying coal beds. Two cores tested coals for gas content and desorption characteristics. Structural and isopachous maps of the coal seams were integrated into a 3D geomodel covering 640 acres beneath the landfill. Critical factors affecting numerical simulations of CBM and simultaneous ECBM production include bed thickness and gas content, cleat spacing, porosity and permeability, and adsorption isotherms. Varying these parameters within geologically reasonable ranges in every possible combination created high, medium, and low scenarios for storage and flow parameters in the geomodel. Results from the model runs were integrated with a Monte-Carlo simulator to quantify the inherent parametric uncertainty in terms of probability.
Results indicate that CO2 sequestration and ECBM recovery are difficult to maximize simultaneously. Ultimate recovery in CBM production may be cut short due to CO2 breakthrough at production wells surrounding the injector. At 80% confidence, several years of CO2 produced from point-sources such as an ethanol plant, cement kiln, or landfill can be locked in the coal beds if the goal is solely to optimize CO2 sequestration. Considering the current rates of CO2 production from the above mentioned point sources, many 160-acre injector sites will be necessary to sequester 20 years of CO2 production from any one of these sources in these thin and shallow coal beds. This is feasible due to small footprint of each injector, but several square miles of open acreage and a pipeline infrastructure around the point source is necessary.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009