Organic petrology, geochemistry, gas content and gas composition of Middle Pennsylvanian age coal beds in the Eastern Interior (Illinois) Basin: Implications for CBM development and carbon sequestration

Abstract

Fifty four samples of coal and organic-rich roof shale strata were collected as part of a coal bed methane exploration program. Following canister desorption to document gas contents, the samples were analyzed by geochemical and petrographic methods. Coal samples were found to have moderate ash yields (avg. 13.5%, dry basis), and high total sulfur contents (avg. 4.3%, dry basis). The average gas content was 1.91m3/ton. Petrographically, the coals were dominated by vitrinite macerals (avg. 81.6%, mmf), especially telovitrinite. By comparison, liptinite (avg. 7.1%, mmf) and inertinite macerals (avg. 11.3%, mmf), were minor in occurrence. Coal samples ranged from high volatile C to high volatile A bituminous in rank (avg. Ro maximum, 0.76%).Shale samples had higher ash yields (avg. 76.1, dry basis), though total sulfur contents were comparable to the coal samples (avg. 4.2%, dry basis). Gas contents were lower than the corresponding coal samples (avg. 0.65m3/ton). Petrographically, the shale samples contained decreased amounts of vitrinite (avg. 25.6%, mmf), and higher amounts of liptinite (avg. 45.4%, mmf) and inertinite (avg. 29.0%, mmf) macerals, relative to the coal samples.Gas obtained from coal and shale beds in the Illinois Basin was relatively pure (high CH4 content). Limited data also indicated that Illinois Basin coals have the ability to adsorb fairly significant amounts of CO2. This suggests that CO2 injection to enhance methane production (ECBM), and/or to sequester CO2 may have some potential. Mineralization in the coals could negatively impact CBM production, but it was found that the majority of the mineralization was present in the roof strata.