25th International Meeting on Organic Geochemistry IMOG 2011

P-448
Genetic and metabolic characterization of methanogen microbial
communities in the Antrim gas shale formation
Cornelia Wuchter 1 , Erin Banning 1 , Nick Drenzek 2 , Marco Coolen 1
1 Woods Hole Oceanogaphic Institution, Marine Chemistry and Geochemistry Department, Woods Hole, MA
02540, United States of America, 2 Schlumberger-Doll Research, Cambridge, MA 02139, United States of
America (corresponding author:c_wuchter@hotmail.com)
Geochemical evidence from the Antrim Shale
(Michigan, USA) indicates that a significant portion of
the economically relevant quantities of natural gas
currently in production has been generated by
microbial methanogenesis over the late Pleistocene
[1]. These biogenic gas deposits are located near the
basin margins where the shale source rock is laden
with organic matter of low thermal maturity and
infiltrated by fresh water flow through a relatively
permeable fracture network [1]. The goal of this study
was to further investigate methanogen community
structure, biogeochemical cycling, and environmental
sensitivity in an effort to enhance formation evaluation
and well completion design.
A 40 m long core was retrieved from the margin of the
Antrim basin and subsampled into sterile desorption
canisters at ten depth horizons corresponding to
distinct lithological and historical gas production units.
Aliquots were subsequently pulverized under an inert
atmosphere and used to initiate incubations with an
array of known methanogen or fermentative bacteria
substrates. Phylogenetic analyses of PCR amplified
core and incubation extracts were also performed by
denatured gradient gel electrophoresis.
Headspace gas analysis of the incubation bottles
revealed substantial methane generation rates at four
different depths that generally correspond to more
organic carbon rich core sections. Interestingly, direct
methane production was stimulated by a typical
methanogen substrate (acetate) at only one depth,
with the other three responding indirectly to the
addition of fermenting bacteria substrates (bitumen,
glucose and yeast extract). Bacterial and archeal 16S
rRNA genes recovered from the incubation bottles
and subsequently DNA fingerprinted revealed a
correspondingly diverse microbial population. Similar
findings have been reported for methanogenic
consortia from a variety of terrestrial and coastal
habitats that can only be isolated after enrichment in a
fermenting co-culture, implying that the hydrogenproducing
fermenting bacterium provides the
methanogenic substrate at low, environmentally
relevant levels [2]. Combined, these results suggest
that biogenic shale gas generation is likewise reliant
on low substrate fluxes provided by fermenting
bacteria. Further research is now underway to isolate
both fermenting bacteria and methanogenic archaea
from the shale formation and constrain the kinetics of
stimulated methane production from gas shale
communities.
References:
[1] Martini et al., 2003. AAPG 87 (8), 1355-1375.
[2] Sakai et al., 2007. AEM doi:10.1128/AEM.03008-
06, 4326-4331.
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