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| Titel |
Understanding NMR relaxometry of partially water-saturated rocks |
| VerfasserIn |
O. Mohnke, R. Jorand, C. Nordlund, N. Klitzsch |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 19, no. 6 ; Nr. 19, no. 6 (2015-06-16), S.2763-2773 |
| Datensatznummer |
250120741
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| Publikation (Nr.) |
 copernicus.org/hess-19-2763-2015.pdf |
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| Zusammenfassung |
Nuclear magnetic
resonance (NMR) relaxometry measurements are commonly used to characterize
the storage and transport properties of water-saturated rocks. Estimations of
these properties are based on the direct link of the initial NMR signal
amplitude to porosity (water content) and of the NMR relaxation time to pore
size. Herein, pore shapes are usually assumed to be spherical or cylindrical.
However, the NMR response at partial water saturation for natural sediments
and rocks may differ strongly from the responses calculated for spherical or
cylindrical pores, because these pore shapes do not account for water menisci
remaining in the corners of desaturated angular pores. Therefore, we consider
a bundle of pores with triangular cross sections. We introduce analytical
solutions of the NMR equations at partial saturation of these pores, which
account for water menisci of desaturated pores. After developing equations
that describe the water distribution inside the pores, we calculate the NMR
response at partial saturation for imbibition and drainage based on the
deduced water distributions.
For this pore model, the NMR amplitudes and NMR relaxation times at partial
water saturation strongly depend on pore shape, i.e., arising from the
capillary pressure and pore shape-dependent water distribution in desaturated
pores with triangular cross sections. Even so, the NMR relaxation time at
full saturation only depends on the surface-to-volume ratio of the pore.
Moreover, we show the qualitative agreement of the saturation-dependent
relaxation-time distributions of our model with those observed for rocks and
soils. |
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