Injection of Biogenic Landfill Gas into Coal Seams for Enhanced Coalbed Natural Gas Recovery and Carbon Sequestration

Timothy R. Carr¹, K. David Newell¹, James G. Blencoe², and Saibal Bhattacharya^1
1 Kansas Geological Survey, University of Kansas, Lawrence, KS
² Oak Ridge National Laboratory, Oak Ridge, TN

Landfills are the largest source of anthropogenic methane (CH₄) emissions in the USA, annually totaling 8.14 Mt (0.38 trillion cubic feet). Landfill gas (LFG) is a low-BTU gas composed of approximately 50% methane CH₄, 40% carbon dioxide (CO₂), and 10% miscellaneous gases, including non-methane volatile organic compounds (NMVOCs). Most CH₄ and CO₂ generated in solid-waste landfills is flared and vented -- a practice that ignores environmental impacts and potential economic value.

A possibly profitable economic option involves injecting LFG, or a CO₂ enriched residual LFG gas into subsurface coal seams. Because CO₂ and NMVOCs are preferentially adsorbed on coal surfaces, the CH₄ concentration of LFG could be increased as it flows through a coal seam from an injection well toward a nearby production well. In addition, adsorbed CH₄ present in the coal prior to LFG injection could be released as sorption proceeds, allowing additional amounts of CH₄ to be produced. In this way, both profitable CH₄ production and cost-effective CO₂ sequestration are realized.

This concept is being tested through field, laboratory, and simulation studies by injecting LFG derived from a large landfill in the Kansas City metropolitan area into underlying Middle Pennsylvanian coals. Sorption/desorption experiments provide data to model gas behavior during and after LFG injection into an underground coal seam. Gas flow-through experiments will help understand permeability changes due to swelling as LFG is adsorbed onto the coal and CH₄ is desorbed from it. Widespread distribution of organic shale and coalbeds provide potential targets for such value-added sequestration.