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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 22, issue 3
Hydrol. Earth Syst. Sci., 22, 1713-1729, 2018
https://doi.org/10.5194/hess-22-1713-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Hydrol. Earth Syst. Sci., 22, 1713-1729, 2018
https://doi.org/10.5194/hess-22-1713-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Mar 2018

Research article | 08 Mar 2018

Hydraulic characterisation of iron-oxide-coated sand and gravel based on nuclear magnetic resonance relaxation mode analyses

Stephan Costabel1, Christoph Weidner2,a, Mike Müller-Petke3, and Georg Houben2 Stephan Costabel et al.
  • 1Federal Institute for Geosciences and Natural Resources, Wilhelmstraße 25–30, 13593 Berlin, Germany
  • 2Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany
  • 3Leibniz Institute for Applied Geophysics, Stilleweg 2, 30655 Hannover, Germany
  • acurrent address: North Rhine Westphalian State Agency for Nature, Environment and Consumer Protection, Leibnizstr. 10, 45659 Recklinghausen, 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 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 estimation of 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 consider 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.

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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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