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| Titel |
Impact on the deep biosphere of CO2 geological sequestration in (ultra)mafic rocks and retroactive consequences on its fate |
| VerfasserIn |
Bénédicte Ménez, Emmanuelle Gérard, Céline Rommevaux-Jestin, Sébastien Dupraz, François Guyot, Helgi Arnar Alfreðsson, Sigurdur Reynir Gislason, Holmfridur Sigurdardottir |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043169
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| Zusammenfassung |
| Due to their reactivity and high potential of carbonation, mafic and ultramafic rocks constitute
targets of great interest to safely and permanently sequestrate anthropogenic CO2 and thus,
limit the potential major environmental consequences of its increasing atmospheric level. In
addition, subsurface (ultra)mafic environments are recognized to harbor diverse and active
microbial populations that may be stimulated or decimated following CO2 injection (±
impurities) and subsequent acidification. However, the nature and amplitude of the involved
biogeochemical pathways are still unknown. To avoid unforeseen consequences at all time
scales (e.g. reservoir souring and clogging, bioproduction of H2S and CH4), the impact of
CO2 injection on deep biota with unknown ecology, and their retroactive effects on the
capacity and long-term stability of CO2 storage sites, have to be determined. We present
here combined field and experimental investigations focused on the Icelandic pilot
site, implemented in the Hengill area (SW Iceland) at the Hellisheidi geothermal
power plant (thanks to the CarbFix program, a consortium between the University of
Iceland, Reykjavik Energy, the French CNRS of Toulouse and Columbia University in
N.Y., U.S.A. and to the companion French ANR-CO2FIX project). This field scale
injection of CO2 charged water is here designed to study the feasibility of storing
permanently CO2 in basaltic rocks and to optimize industrial methods. Prior to
the injection, the microbiological initial state was characterized through regular
sampling at various seasons (i.e., October ‘08, July ‘09, February ‘10). DNA was
extracted and amplified from the deep and shallow observatory wells, after filtration of
20 to 30 liters of groundwater collected in the depth interval 400-980 m using a
specifically developed sampling protocol aiming at reducing contamination risks. An
inventory of living indigenous bacteria and archaea was then done using molecular
methods based on the amplification of small subunit ribosomal RNA genes (SSU
rDNAs). The stratigraphic levels targeted to store the injected CO2 as aqueous
phase harbor numerous new species close to cultivable species belonging to the
genus Thermus or Proteobacteria species known to be linked in particular with the
hydrogen and iron cycles. After injection, the evolution of these microbial communities
will be monitored using the Denaturing Gradient Gel Electrophoresis technique.
Beyond the ecological impact of storing high levels of CO2 in deep environments,
particularly important is the ability of intraterrestrial microbes to potentially interact
with the injected fluids. For example, carbonation has been shown to be strongly
influenced by microbiological activities that can locally modify pH and induce
nucleation of solid carbonates. To improve the understanding of these processes
and to better constrain the influence of deep biota on the evolving chemical and
petrophysical properties of the reservoir, an experimental and numerical modeling is
carried out in parallel, using model strains representative of the subsurface (including
acetogens, sulphate and iron reducing bacteria), as single-species or consortia. A
set of batch experiments in presence of crushed olivine or basalts was especially
designed to evaluate how microbial activity could overcome the slow kinetics of
mineral-fluid reactions and reduce the energy needed to hasten the carbonation process. |
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