Quantification of microporosity by nuclear magnetic resonance relaxation of water imbibed in porous media

Abstract

Abstract. On the basis of the nuclear magnetic resonance (NMR) relaxation of imbibed water, we evaluated the interparticle and intraparticle pore sizes in packed beds of silica materials of known particle sizes and microporous structure. The NMR relaxation distribution is scaled by the surface relaxivity parameter p, which incorporates a surface area to volume ratio (So/Vo) term, to yield a corresponding pore size distribution. The NMR-derived pore sizes of nonporous silica sand agreed with the expected interparticle pore sizes estimated from the morphology of a packed bed of spheres of comparably sized particles. The NMR-derived intraparticle pore size for porous silica was also in good agreement with reported values for the silica materials studied. Scaling of the NMR relaxation corresponding to interparticle water by the same surface interaction parameter to yield interparticle pore size in high-surface area porous silica material, however, grossly underestimated interparticle pore size. In these high-surface area materials the intraparticle micropores provide a higher contribution to the N 2 measured surface area relative to the contribution from interparticle macropores. When the NMR relaxation method was used to evaluate the pore space in the Borden Aquifer material, the NMRderived pore sizes agreed with those observed in scanning electron micrographs as well as pore sizes estimated from the morphology of packed beds of comparably sized particles. For soils and aquifer materials of low to moderate surface area the NMR-derived porosity determination may be used to adequately evaluate both solute transporting and sorbing pore sizes. IntroductionThe fate and transport of pollutants in terrestrial and aquatic ecosystems are influenced by the heterogeneity of the sotbent matrix. In modeling solute transport, assumptions regarding the sorption mechanisms and the microgeometry of sotbents must be made. Experimental data is needed to calibrate model parameters which describe the pore structure and hydraulic properties. There is, however, a lack of process- The principle methods for pore structure analysis are gas adsorption/condensation and mercury porosimetry [Gregg and Sing, 1977]. In heterogeneous porous media characterized by a broad range of pore sizes, the two methods are complementary [Ball et al., 1990] in that the former is capable of measuring sizes less than 0.05/xm and the latter is better suited to measure sizes greater than 0.05/xm. There are limitations inherent to each of these methods, however. Both gas adsorption and mercury porosimetry measure the smallest constriction in a porous matrix rather than the pore radius [Gallegos et al., 1988]. In addition, these methods require removal of the pore fluid prior to analysis. Desiccation may cause irreversible 2697

Influence of drying–wetting cycles on soil-water characteristic curve of undisturbed granite residual soils and microstructure mechanism by nuclear magnetic resonance (NMR) spin-spin relaxation time (T2) relaxometry

“…Desiccation may cause irreversible changes in pore structure, which in turn will affect the actual POSD of the soils. The Image analysis or Microscopy requires approach a large quantity of two-dimensional information for the desired three-dimensional pore structure information and it is time-consuming (Gallegos and Smith 1988;Hinedi et al 1997;Giesche 2006;Kate and Gokhale 2006;Minagawa, et al 2008;Benjamini et al 2014;Wang et al 2016). None of those methods are suitable for this present study because the tested soil is a special kind of low density (dry density, ρ d =1.30 g/cm 3 ) granite residual soil with grain size distribution ranging from gravel to clay.…”

“…Recently, numerous studies reported the potentiality of NMR relaxometry to assess the POSD of porous media in a fast and non-destructive way (Kleinberg 1994;Strange et al 1993; Hinedi al. 1997;Milia et al 1998;Dunn et al 2002;Ramia et al 2010).…”

Nuclear magnetic resonance imaging of water content in the subsurface

“…This time constant is generally measured in controlled laboratory experiments (e.g. Hinedi et al 1997) and in borehole logging by switching the static applied magnetic field for various lengths of time. Tlis procedure is not possible for the surfkce geophysicalmeasurementswhere the earth's magnetic field is used.…”

Nuclear Magnetic Resonance Imaging of Water Content in the Subsurface

“…This time constant is generally measured in controlled laboratory experiments (e.g. Hinedi et al 1997) and in borehole logging by switching the static applied magnetic field for various lengths of time. This procedure is not possible for the surface geophysical measurements where the earth's magnetic field is used.…”