Gas Origin in Coals of the Blackhawk Formation,
Coals of the Blackhawk Formation locally contain a world class in-situ methane resource base that is estimated to exceed 30 billion standard cubic feet of gas per sq mile. Following recent coring of the primary coal groups at the Castlegate CBM field, detailed carbon isotopic investigations of desorbed gases with mixed composition (C1, C2, C3, CO2) while strongly indicating a thermogenic origin, suggest that not all gas within the coal is internally sourced from humic kerogens. Rather, the isotopic signatures and gas composition indicate that the gas in place has a mixed origin from both internal and external sources, the later likely having being generated by type I & II kerogens from the underlying Mancos Shales, and adsorbed during uplift.
Detailed study of both subsurface and outcrop data, indicate
that the migration pathway for secondary thermogenic
enrichment is the likely combination of coal seam positioning relative to large