The Economic Interplay Between CO₂ Sequestration and Enhanced CH₄ Production from Coal Beds: Two Scenarios from Eastern Kansas

Saibal Bhattacharya¹, K. D. Newell¹, and Timothy R. Carr^2
1Kansas Geological Survey, University of Kansas, Lawrence, KS
²Dept of Geology and Geography, West Virginia University, Morgantown, WV

Eastern Kansas is underlain by several thin Pennsylvanian coal beds (1 to 4 ft), which range in rank from high-volatile C to A bituminous. As-received gas contents are as high as 350 scf/ton, and several coal beds commonly produce in a single well. Coal can adsorb approximately twice the volume of CO₂ than the desorbed CH₄, and therefore offer potential for carbon sequestration with enhanced coal-bed methane (ECBM) recovery.

Two scenarios were simulated for injection of CO₂-rich effluent gases generated respectively by a cement kiln and a landfill located in eastern Kansas into underlying coal beds. Critical factors affecting model performance include bed thickness and gas content, cleat spacing, porosity, and permeability, and adsorption isotherms. Results indicate that a large 5-spot pattern (160-acre spacing) utilizing a center-point injector can sequester CO₂ for years while delaying ECBM recovery. Reduced well spacing facilitates faster ECBM recovery, but limits sequestration volume due to early CO₂ breakthrough. Given bed thicknesses, cleat permeabilities, and conventional well spacing in the modeled areas, several dozen injection wells are needed to sequester the CO₂ emitted by these point sources.

Monte-Carlo cost/revenue simulation determined minimum geologic requirements to economically sequester CO₂ at the expense of delayed ECBM production. Depending on gas prices, a 15 to 30% increase in ECBM recovery is needed to justify the cost of a large 5-spot pattern which requires higher pipeline expenses. As a necessary next step, a small-scale pilot project should be initiated to validate modeling results.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas