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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2017-364
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
04 Aug 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).
Hydraulic characterisation of iron oxide-coated sand and gravel based on nuclear magnetic resonance relaxation modes analyses
Stephan Costabel1, Christoph Weidner2,a, Mike Müller-Petke3, and Georg Houben2 1Federal Institute for Geosciences and Natural Resources, Berlin, Wilhelmstraße 25–30, 13593, Germany
2Federal Institute for Geosciences and Natural Resources, Hannover, Stilleweg 2, 30655, Germany
3Leibniz Institute for Applied Geophysics, Hannover, Stilleweg 2, 30655, Germany
acurrent address: North Rhine Westphalian State Agency for Nature, Environment and Consumer Protection, Recklinghausen, Leibnizstr. 10, 45659, Germany
Abstract. The capability of nuclear magnetic resonance (NMR) relaxometry to characterise hydraulic properties of iron oxide-coated sand and gravel was evaluated in a laboratory study. Past studies have shown that the presence of paramagnetic iron oxides and large pores as present in coarse sand and gravel disturbs the otherwise linear relationship between relaxation time and pore size. Consequently, the commonly applied empirical approaches fail when deriving hydraulic quantities from NMR parameters. Recent research demonstrates that higher relaxation modes must be taken into account to relate the size of a large pore to its NMR relaxation behaviour in the presence of significant paramagnetic impurities at its pore wall. We performed NMR relaxation experiments with water-saturated natural and reworked sands and gravels, coated with natural and synthetic ferric oxides (goethite, ferrihydrite) and show that the impact of the higher relaxation modes increases significantly with increasing iron content. Since the investigated materials exhibit narrow pore size distributions, and can thus be described by a virtual bundle of capillaries with identical apparent pore radius, recently presented inversion approaches allow for estimating a unique solution yielding the apparent capillary radius from the NMR data. We found the NMR-based apparent radii to correspond well to the effective hydraulic radii estimated from the grain size distributions of the samples for the entire range of observed iron contents. Consequently, they can be used to estimate the hydraulic conductivity using the well-known Kozeny-Carman equation without any calibration that is otherwise necessary when predicting hydraulic conductivities from NMR data. Our future research will focus on the development of relaxation time models that allow for broader pore size distributions. Furthermore, we plan to establish a measurement system based on borehole NMR for localising iron clogging and controlling its remediation in the gravel pack of groundwater wells.

Citation: Costabel, S., Weidner, C., Müller-Petke, M., and Houben, G.: Hydraulic characterisation of iron oxide-coated sand and gravel based on nuclear magnetic resonance relaxation modes analyses, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-364, in review, 2017.
Stephan Costabel et al.
Stephan Costabel et al.
Stephan Costabel et al.

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Short summary
Laboratory experiments using water-filled sand and gravel samples with significant contents of iron oxide coatings were performed to identify the relationship between effective hydraulic radius and nuclear magnetic resonance (NMR) response. Our interpretation approach for the NMR data leads to reliable estimates of hydraulic conductivity without calibration, but is limited to coarse material for physical reasons. An NMR-based observation system for iron clogging in boreholes is planned.
Laboratory experiments using water-filled sand and gravel samples with significant contents of...
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