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| Titel |
Spatiotemporal observation of transport in fractured rocks |
| VerfasserIn |
Johannes Kulenkampff, Frieder Enzmann, Marion Gründig, Hellmuth Mittmann, Martin Wolf |
| 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 |
250033116
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| Zusammenfassung |
| A number of injection experiments in different rocks types have been conducted with
positron emission-process-tomography using a high-resolution "small-animal" PET-scanner
(ClearPET by Raytest, Straubenhardt) for the monitoring of transport processes. The fluids
are labelled with positron-emitting isotopes like e.g. 18F-, 124I- or dissolvable
complexes like K3[58Co(CN)6], without affecting their physico-chemical properties.
The annihilation radiation from individual decaying tracer atoms is detected with
high sensitivity, and the tomographic reconstruction of the recorded events yields
quantitative 3D-images of the tracer distribution. Sequential tomograms during
and after tracer injection are used for the spatiotemporal observation of the fluid
transport.
Raw data is corrected with respect to background radiation (randoms) and Compton
scattering, which turns out to be much more significant in rocks than in common biomedical
applications. Although in principle these effects are exactly known, we developed and apply
simplified and fast correction methods. Deficiencies of these correction algorithms generate
some artefacts, that cause the lower limit of the tracer concentration in the order of 1 kBq/μl
or about 107 atoms/μl, still outranging other methods (e.g. NMR or resistivity tomography)
by many orders of magnitude.
New 3D-visualizations of the process-tomograms in fractured rocks show strongly
localized and complex flow paths and in parts unexpected deviations from the fracture
structures as deduced from μCT-images. Such results demonstrate the potential of large
discrepancies between μCT-derived parameters like pore volume and specific surface area
and the hydraulic effective parameters as derived by means of the PET-process-tomography.
We conclude that such discrepancies and the complexity of the transport process in natural
heterogeneous porous media illustrates the limits of parameter determination methods from
model simulations based on structural pore-space models – in particular as long as the
simulations are not verified by experimental data. |
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