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| Titel |
Combined 3D high-resolution PET and CT measurements with lattice Boltzmann simulations of fluid flow in heterogeneous material |
| VerfasserIn |
Martin Wolf, Johannes Kulenkampff, Frieder Enzmann, Marion Gründig, Michael Richter, Johanna Lippmann-Pipke |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250055063
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| Zusammenfassung |
| The joint research project “Dynamics of drowned and flooded salt mines and their overlaying
rocks” aimed at exemplarily and comprehensively clarifying causes, processes and effects of
damages caused by abandoned historical potassium mining in Staßfurt, Germany [1]. Funded
by the BMBF (Bundesministerium für Bildung und Forschung) ten universities,
research facilities and companies were coordinated by the BGR (Bundesanstalt für
Geowissenschaften und Rohstoffe). The IRC - Research Site Leipzig contributed small scale
laboratory experiments of flow and transport process observations in drilling cores from
hydrologic relevant regional lithologies and the matching of fluid flow patterns with high
resolution CT imaging data and structure-controlled model simulations obtained
and conducted by colleagues from JGUM [2]. This close collaboration aimed at
enhancing the comprehension of small scale fluid flow in heterogeneous natural porous
media.
Visualization of fluid flow in homogeneous porous as well as in fractured heterogeneous
media was conducted with a preclinical PET scanner with a spatial resolution of 1 mm and a
temporal resolution of 1 minute [3]. Drill cores from anhydrite, sandstone and rock salt
formations of the Staßfurt salt dome were examined with continuous flow-through
experiments. Pulses of radiotracer solutions ([18F]KF and [124I]KI) were injected and in
situ PET-observations of the tracer propagation were conducted throughout the
course of several hours and weeks, depending on the sample permeability. The flow
behavior can be described with heterogeneous and process-dependent parameter
distributions, like effective volume, permeability and dispersion rates. Based on μXCT
measurements with a spatial resolution of 65.3 μm the percolating pore space, including
all connected pores and fractures and the maximal inner surface, was quantified
[2].
This “GeoPET” method is an excellent tool for direct quantitative spatiotemporal
visualization of tracer transport in heterogeneous rocks on core scale [3, 4]. Combined
interpretation of μXCT and PET data enables deepened understanding on causes and effects
of the structural constraints (pore space, cleavages etc.) on fluid flow patterns, enables
to stereotype combined structural characteristics and flow path topologies and to
determine the ratio between total and effective pore volume. The latter is for instance
revealed by observable fingering phenomena in extended fractures. The fraction of the
internal surface of a rock sample in contact with the mobile fluid – the effective
reactive surface area – decreases with increasing localization of actual transport paths.
Therefore, combined PET-CT data interpretation enables to realistically describe the
considerably narrowed potential of dissolution and sorption reactions in heterogeneous and
fractured media. In combination with simulated data the flow velocity patterns were
quantified along the pathways, and they appeared highly variable within the fractures. In
saline rocks we observed that localized high flow velocities may locally stimulate
the salt dissolution and cause the widening of fracture cross sections. Such self
energizing mechanisms may lead to increasing permeabilities, flow velocities and flow
rates.
The complex flow patterns and the different resolutions of the data sets require scale
independent comparison methods. We thus applied variography [4], which also could be
applicable as simple method for upscaling to the field scale.
[1] Gerardi, J. (2006) Report BGR, p. 79.
[2] Enzmann, F. et al. (2010) EDGG, 244, p. 213-224.
[3] Kulenkampff, J. et al. (2008) Phys. Chem. Earth, 33, p. 937-942.
[4] Wolf, M. et al. (2010) EDGG, 244, p. 200-212. |
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