Variability of geochemical properties in a microbially dominated coalbed gas system from the eastern margin of the Illinois Basin, USA

This study outlines gas characteristics along the southeastern margins of the Illinois Basin and evaluates regional versus local gas variations in Seelyville and Springfield coal beds. Our findings suggest that high permeability and shallow (100-250 m) depths of these Indiana coals allowed inoculation with methanogenic microbial consortia, thus leading to widespread microbial methane generation along the eastern marginal part of the Illinois Basin. Low maturity coals in the Illinois Basin with a vitrinite reflectance Ro ~ 0.6% contain significant amounts of coal gas (~ 3 m3/t, 96 scf/t) with ≥ 97 vol.% microbial methane. The amount of coal gas can vary significantly within a coal seam both in a vertical seam section as well as laterally from location to location. Therefore sampling of an entire core section is required for accurate estimates of coal gas reserves.