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
progradational parasequences
of the basin
centered
source rocks in enriching low to medium ranked coal
groups.