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| Titel |
Observational evidence for the long-term integrity of CO2-reservoir caprocks |
| VerfasserIn |
Niko Kampman, Peiter Bertier, Andreas Busch, Jeroen Snippe, Vitaly Pipich, Jon Harrington, Mike Bickle |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106559
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| Publikation (Nr.) |
 EGU/EGU2015-6236.pdf |
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| Zusammenfassung |
| Storage of anthropogenic CO2 in geological formations relies on impermeable caprocks as
the primary seal preventing buoyant super-critical CO2 escaping upwards. Although
natural CO2 reservoirs demonstrate that CO2 may be stored safely for millions of
years, uncertainty remains in predicting how caprocks will react in contact with acid
CO2-bearing brines. This uncertainty is a significant barrier to risk assessment and
consequently implementation of carbon capture and storage schemes. Prediction of caprock
behavior is based primarily on theoretical modelling and laboratory experiments.
However, the coupled reactive transport phenomena cannot be faithfully reproduced
in laboratory experiments over sufficient timescales, theoretical models have not
been calibrated against observational data and existing studies on natural caprocks
have not resolved mineral reactions. Here we report the first detailed description
and interpretation of a CO2 reservoir-caprock system exposed to CO2 over ~ 105
years, a time-scale comparable with that needed for effective geological carbon
storage. Fluid-mineral reactions in the basal seven cm of the caprock, driven by
diffusion of CO2 and minor H2S from the underlying reservoir, result in dissolution of
haematite, dolomite and K-feldspar and precipitation of Fe-bearing dolomites, gypsum,
pyrite and illite. The mineral dissolution reactions within the caprock generate
transient increases in porosity but the propagation of these mineral reaction fronts is
retarded by the reaction stoichiometry and mineral precipitation. Neutron scattering
measurements indicate that the decrease in tortuosity and the fractal dimensions of
the pore-network following mineral dissolution is only partly offset by mineral
precipitation, implying a non-recoverable increase in effective diffusivity. Analytical
modeling is used to extract kinetic data from the geometry of the mineral reaction
fronts and numerical reactive transport modeling is used to place constraints on the
time-scales of the alteration. The results attest to the significance of transport-limited
reactions to the long-term integrity of sealing behavior in caprocks exposed to CO2. |
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