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| Titel |
CO2 permeability of fractured cap rocks - experiments and numerical simulations (CO2Seals) |
| VerfasserIn |
Ines Rick (Draeger), Christoph Clauser |
| 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 |
250034321
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| Zusammenfassung |
| In CO2 sequestration and underground gas storage the sealing capacity of a cap rock is of
paramount importance. The main question is therefore how the leakage of CO2 through
fissures and faults within the cap rock may affect the CO2 sealing efficiency of
low-permeable seal lithotypes. In many cases, these structures provide the main pathways for
leakage of CO2.
Here, we provide an overview of one part of the joint research project CO2Seals, which deals
with the effect of structural features - such as tectonic faults and fissures in the overburden -
on the migration of CO2 in addition to mineralogical, petrophysical, and geochemical
properties of different lithotypes.
The primary contribution of the entire project consists of an improvement of the present
quantitative understanding of CO2 transport and retention processes and associated
interactions in cap rocks between rock and CO2 or brine.
To this end, we are adapting different numerical tools for simulating the relevant
petrophysical and geochemical processes of CO2 in cap rocks, in close operation with:
(1) large-scale CO2-percolation experiments on fractured cap rock samples; (2)
permeability, gas breakthrough, and diffusion experiments; (3) measurements of the
mechanical stability of cap rocks and the geochemical alterations of fault zone rock. The
observed resulting changes in petrophysical properties, such as porosity, relative rock
permeability (CO2 and brine), and fault permeability provide basics for the following
numerical simulations. For example, first permeability tests of a marl and clay cap
rock out of Cretaceous and Jurassic formations revealed gas permeability of 10-18
m2 down to 10-22 m2. In addition, first percolation experiments indicated that
the influence of fault zones on the measured CO2 permeability of clays is very
low.
Furthermore, numerical bench-scale models are performed to provide confidence for the
subsequent transfer to reservoir systems.
Large-scale numerical models were created for this purpose including generic structural
geological faults and comprising Mesozoic and Cenozoic formations of the Northern German
Basin. The mass of CO2 retained by a multi-barrier system including reservoirs and cap rocks
is estimated by taking into account hydraulic property values of known fault systems and
predicted or measured leakage rates, also from natural analogues.
As a result, we provide conclusions with respect to the stability and tightness of cap rocks
exposed to CO2 for long periods. Furthermore, potential CO2 leakage scenarios on different
size- and time-scales are generated in addition to the characterization of the CO2 sealing
efficiency of low-permeable cap rocks.
The CO2Seals project is funded by the R&D program GEOTECHNOLOGIEN of the German
Federal Ministry of Education and Research (BMBF). It is a joint research project of RWTH
Aachen University and the Karlsruhe Institute of Technology (KIT). The project is co-funded
and accompanied scientifically by the industry partner Shell International Exploration and
Production, Netherlands. |
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