TY - JOUR A1 - Binley, A. A1 - Kruschwitz, Sabine A1 - Lesmes, D. A1 - Kettridge, N. T1 - Exploiting the temperature effects on low frequency electrical spectra of sandstone: a comparison of effective diffusion path lengths JF - Geophysics N2 - A number of recent investigations have highlighted the potential value of using relaxation times derived from electrical spectra to infer key physical properties of permeable rocks. To date, most studies have assumed a grain size or pore throat as a measure of the length scale of the ionic diffusive process, although this has been challenged in recent experimental investigations. We compare the electrical spectra of three sandstones, adopting a new approach in which the temperature of the rock samples is perturbed and the relaxation time measured as a function of temperature. Our results suggest that, for the sandstones tested here, the effective diffusion coefficient should be considered as a function of the electrical tortuosity. These findings may help explain the apparent long relaxation times observed in low-permeability rocks in recent experimental studies. We also highlight the need to account for temperature in related studies of electrical spectra. KW - Grain size KW - Porosity KW - Rocks KW - Spectral induced polarization KW - Temperature KW - Sandstone KW - Saturation KW - Diffusion PY - 2010 DO - https://doi.org/10.1190/1.3483815 SN - 0016-8033 VL - 75 IS - 6 SP - A43 EP - A46 PB - Soc. CY - Tulsa, Okla. [u.a.] AN - OPUS4-23860 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kruschwitz, Sabine A1 - Binley, A. A1 - Lesmes, D. A1 - Elshenawy, A. T1 - Textural controls on low-frequency electrical spectra of porous media JF - Geophysics N2 - The results from several laboratory studies of the relationships between electrical polarization and physical properties of porous media have prompted interest in the potential use of low-frequency electrical spectra to qualitatively or quantitatively map variation in hydrogeologic properties in the field. Compiling several published and unpublished data sets, supported by new measurements, we have examined the low-frequency electrical spectra of a range of natural and artificial porous media to assess the generality of proposed relationships between electrical and physical properties. Our work confirms a significant positive correlation between the magnitude of electrical polarization (quantified as imaginary conductivity at a specific frequency) and the surface-area/pore-volume ratio Spor. Analyzing the parameters of ageneralized Cole-Cole resistivity relaxation model fitted to many electrical spectra, we observe two apparent controls on the electrical relaxation. For samples with abundant relatively large pore throats, we observe a distinct increase in the time constant of the model with modal pore-throat size, in accordance with classical electrical relaxation models. However, for media with pore structures dominated by small pore throats, the diffusion-length scales do not appear to be controlled by modal pore-throat size. We conclude that for such media, the microstructure of the network of small pores leads to some connectivity of diffusion paths; thus, these samples exhibit relatively large time constants. There is potential value in addition to limitations when using electrical spectra to estimate physical properties of porous media, and we see the need for more appropriate generalized theories of electrical polarization in hydrogeologic media. KW - Geophysical techniques KW - Terrestrial electricity KW - Spectral induced polarization KW - Temperature KW - Sandstone KW - Saturation KW - Diffusion PY - 2010 DO - https://doi.org/10.1190/1.3479835 SN - 0016-8033 VL - 75 IS - 4 SP - WA113 EP - WA123 PB - Soc. CY - Tulsa, Okla. [u.a.] AN - OPUS4-23861 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -