Geomodel Development and Simulation Studies for Possible Carbon Dioxide Sequestration and Enhanced Coalbed Gas Recovery Beneath a Major Kansas City Landfill

S. Bhattacharya¹, K. D. Newell¹, T. R. Carr¹, and J. G. Blencoe². (1) Kansas Geological Survey, University of Kansas, Lawrence, KS, (2) Oak Ridge National Laboratory, Oak Ridge, TN 

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Pennsylvanian coal and gas shale units, which underlie the Johnson County Landfill serving Kansas City, respectively record maximum as-received gas contents of 79 scf/ton (Bevier coal, 570-ft depth) and 22 scf/ton (Anna Shale, 421 ft). In-place gas in five coals and three shales beneath the landfill is calculated to be 986 mcf/acre. Isotopic and chemical analyses of desorption gases indicate that they are of mixed biogenic/thermogenic origin. Proximate analyses indicate the coals are high-volatile C to B bituminous ranks. The coals and gas shales are undersaturated with respect to their gas content, and the degree of saturation decreases with depth.

Daily production of landfill gas from the Johnson County Landfill is approximately 2.5 mmcf, of which 50% is methane (CH₄) and 50% is carbon dioxide (CO₂) and non-methane volatile organic compounds. About 4.5 years of landfill CO₂ production can be expected to be sequestered under the 960-acre site assuming that CO₂ can be imbibed on a 2:1 ratio compared to gas originally adsorbed. 

A multi-layer 3D-simulation study was carried out on a five-spot (one injector, four producers) pattern located on 40 acres to evaluate the volumes of CO₂ adsorbed and CH₄ produced, and respective breakthrough times. In preparation for a possible pilot demonstration, Monte Carlo simulation incorporating uncertainties in petrophysical parameters and recoveries was conducted for net-present-value (NPV) estimation. This proposed value-added model of CO₂ sequestration is expected to benefit unconventional gas production by increasing the rate and amount of CH₄ desorbed from the gas-bearing coal and shale units.