Relaxation in a Natural Soil: Comparison of Relaxometric Imaging, T1– T2 Correlation and Fast-Field Cycling NMR

Haber‐Pohlmeier, Sabina

doi:10.2174/1874769801003010057

Cited by 13 publications

(18 citation statements)

References 18 publications

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“…Although called the ratio . Such features have also been observed for fluids within soil [43,44], cement [16,45], ceramics [46], and porous catalysts [14,15].…”

Section: T 1 and T 2 Relaxation In Porous Mediamentioning

confidence: 59%

Obtaining T 1 - T 2 distribution functions from 1-dimensional T 1 and T 2 measurements: The pseudo 2-D relaxation model

Williamson

Röding

Galvosas

et al. 2016

Journal of Magnetic Resonance

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We present the pseudo 2-D relaxation model (P2DRM), a method to estimate multidimensional probability distributions of material parameters from independent 1-D measurements. We illustrate its use on 1-D T1 and T2 relaxation measurements of saturated rock and evaluate it on both simulated and experimental T1-T2 correlation measurement data sets. Results were in excellent agreement with the actual, known 2-D distribution in the case of the simulated data set. In both the simulated and experimental case, the functional relationships between T1 and T2 were in good agreement with the T1-T2 correlation maps from the 2-D inverse Laplace transform of the full 2-D data sets. When a 1-D CPMG experiment is combined with a rapid T1 measurement, the P2DRM provides a double-shot method for obtaining a T1-T2 relationship, with significantly decreased experimental time in comparison to the full T1-T2 correlation measurement.

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“…Although called the ratio . Such features have also been observed for fluids within soil [43,44], cement [16,45], ceramics [46], and porous catalysts [14,15].…”

Section: T 1 and T 2 Relaxation In Porous Mediamentioning

confidence: 59%

Obtaining T 1 - T 2 distribution functions from 1-dimensional T 1 and T 2 measurements: The pseudo 2-D relaxation model

Williamson

Röding

Galvosas

et al. 2016

Journal of Magnetic Resonance

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“…These methods are mostly inconvenient for investigating flow processes in soils, however, because the lower limit of these methods is on the order of some hundred micrometers per second, and flow velocities in soils are mostly slower. Second, the major obstacle for using MRI in soils is the inherent fast transverse relaxation, which is in the range between 0.1 and 10 ms (Hall et al, 1997; Votrubova et al, 2000; Haber‐Pohlmeier et al, 2010). The reasons for this are the presence of paramagnetic impurities and small pore sizes, because T 2 relaxation is caused by the dephasing of local magnetic moments in local magnetic field gradients, which are created at solid–liquid interfaces.…”

Section: Basics Of Magnetic Resonance Imagingmentioning

confidence: 99%

Water Flow Monitored by Tracer Transport in Natural Porous Media Using Magnetic Resonance Imaging

Haber‐Pohlmeier

Bechtold

Stapf

et al. 2010

Vadose Zone Journal

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Magne c resonance imaging (MRI) was applied to the study of fl ow processes in model and natural soil cores. Flow veloci es in soils are mostly too slow to be monitored directly by MRI fl ow velocity imaging. Therefore, we used for the fi rst me diethylenetriaminepentaacetate in the form Gd-DTPA 2− as a tracer in spin echo mul slice imaging protocols with strong weigh ng of longitudinal relaxa on me T 1 for probing slow fl ow veloci es in soils. Apart from its chemical stability, the main advantage of Gd-DTPA 2− is the anionic net charge in neutral aqueous solu on. We showed that this property hinders adsorp on at soil mineral surfaces and therefore retarda on. We found that Gd-DTPA 2− is a very convenient conserva ve tracer for the inves ga on of fl ow processes in model and natural soil cores. With respect to the fl ow processes in the coaxial model soil column and the natural soil column, we observed totally diff erent fl ow pa erns. In the fi rst case, the tracer plume moved quite homogeneously in the inner highly conduc ve core only and the migra on into the outer fi ne material was very limited. A numerical forward simula on based on independently obtained parameters showed good agreement between experiment and simula on and thus proves the convenience of Gd-DTPA as a tracer in MRI for soil physical inves ga ons. The natural soil core, in contrast, showed a fl ow pa ern characterized by preferen al paths, avoiding dense regions and preferring loose structures. In the case of the simpler model column, the local fl ow veloci es were also calculated by applying a peak tracking algorithm.Abbrevia ons: DTPA, diethylenetriaminepentaacetate; MRI, magne c resonance imaging; NMR, nuclear magne c resonance; rf, radiofrequency; SEMS, spin-echo mul slice.Flow processes in soils control the water and nutrient supply in plants, contaminant transport, and the recharging of aquifers. Natural soils are heterogeneous media with locally varying grain size, pore size, and pore geometry. In addition, highly conductive structures like wormholes and decomposed roots are present. All these factors lead to so-called preferential pathways, along which water fl ows faster vertically than expected from the average fl ow velocity v av [(volume fl ow rate/area)/water content: v av = (Q/A)/θ = J w /θ] but from which water can also diff use laterally into neighboring small-pore-size regions. All these processes can strongly aff ect water redistribution in soils, its bioavailability for plants, and transport of contaminants Clothier et al., 2008). Classical investigations of such processes have been invasive and not temporally resolved. For example, soil cores are infi ltrated with dyes and aft erward sliced and photographed, so that only the static result of fl ow processes can be observed (Wehrhahn et al., 2007). Th e direct observation of such processes in situ is diffi cult due to the opaque nature of the systems. Th erefore, during the past two decades, tomographic methods have become popular for the investigation of soils and soil-r...

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“…Several nondestructive techniques [Roels et al, 2004], including nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) [Carpenter et al, 1993;Leech et al, 2003;Pohlmeier et al, 2008a] and γ ray attenuation [Ferguson and Gardner, 1963;Nielsen, 1972;Nizovtsev et al, 2008], have been applied to probe distributions of water saturation and to study the dynamics of liquid transport in porous materials. The quantitative study of water in porous media using NMR or MRI is limited by the range of pore sizes that can be imaged and the presence of paramagnetic elements in the samples [Chen et al, 2003;Haber-Pohlmeier et al, 2010;Jelinkova et al, 2011;Pohlmeier et al, 2008a]. As an alternative method to visualize fluid flow in porous materials, X-ray imaging can be applied to visualize porosity and equilibrium fluid distributions in porous materials [Bayer, 2005;Nabawy and David, 2016;Pease et al, 2012;Roels and Carmeliet, 2006;Schillaci et al, 2008;Tidwell et al, 2000].…”

Section: Introductionmentioning

confidence: 99%

Effects of microstructure on water imbibition in sandstones using X‐ray computed tomography and neutron radiography

et al. 2017

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Capillary imbibition in variably saturated porous media is important in defining displacement processes and transport in the vadose zone and in low‐permeability barriers and reservoirs. Nonintrusive imaging in real time offers the potential to examine critical impacts of heterogeneity and surface properties on imbibition dynamics. Neutron radiography is applied as a powerful imaging tool to observe temporal changes in the spatial distribution of water in porous materials. We analyze water imbibition in both homogeneous and heterogeneous low‐permeability sandstones. Dynamic observations of the advance of the imbibition front with time are compared with characterizations of microstructure (via high‐resolution X‐ray computed tomography (CT)), pore size distribution (Mercury Intrusion Porosimetry), and permeability of the contrasting samples. We use an automated method to detect the progress of wetting front with time and link this to square‐root‐of‐time progress. These data are used to estimate the effect of microstructure on water sorptivity from a modified Lucas‐Washburn equation. Moreover, a model is established to calculate the maximum capillary diameter by modifying the Hagen‐Poiseuille and Young‐Laplace equations based on fractal theory. Comparing the calculated maximum capillary diameter with the maximum pore diameter (from high‐resolution CT) shows congruence between the two independent methods for the homogeneous silty sandstone but less effectively for the heterogeneous sandstone. Finally, we use these data to link observed response with the physical characteristics of the contrasting media—homogeneous versus heterogeneous—and to demonstrate the sensitivity of sorptivity expressly to tortuosity rather than porosity in low‐permeability sandstones.

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Relaxation in a Natural Soil: Comparison of Relaxometric Imaging, T1– T2 Correlation and Fast-Field Cycling NMR

Cited by 13 publications

References 18 publications

Obtaining T 1 - T 2 distribution functions from 1-dimensional T 1 and T 2 measurements: The pseudo 2-D relaxation model

Obtaining T 1 - T 2 distribution functions from 1-dimensional T 1 and T 2 measurements: The pseudo 2-D relaxation model

Water Flow Monitored by Tracer Transport in Natural Porous Media Using Magnetic Resonance Imaging

Effects of microstructure on water imbibition in sandstones using X‐ray computed tomography and neutron radiography

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