Predicting the Dielectric Response of Saturated Sandstones Using a 2-electrode Measuring System

Frontiers in Physics

Kirichek, Alex¹  Chassagne, Claire²  Ghose, Ranajit² 

[1] Deltares, Netherlands;Department of Hydraulic Engineering, Faculty of Civil Engineering and Geosciences, TU Delft, Netherlands

关键词: Dielectric Spectroscopy;    sandstone;    Electrode polarization;    impedance;    2-electrode setup;   

DOI  :  10.3389/fphy.2018.00148

学科分类：物理（综合）

来源: Frontiers

【 摘 要 】

4-electrode setups are usually used to measure the dielectric response (complex conductivity)of sandstones, as it is known that 2-electrode systems are sensitive to unwantedelectrode polarization at low frequency. Moreover, electrode polarization (EP) occurs inthe frequency range where the characteristic relaxation associated to the grain size also occurs, which can therefore theoretically be assessed using 4-electrode setups. Nonetheless, we find that other parameters of interest (porosity, salinity) can easily be extracted from the frequency range 1 - 10 kHz, beyond the one affected by EP using a 2 electrode setup. An additional unwanted effect (”pseudo-inductance”) is observed in the frequency range 10 kHz - 1 MHz during our experiments. Even though the origin of this effect remains unknown, it is shown to be correlated with the ionic strength of the system and the electrode separation. The bulk polarization region, i.e. the region of intermediate frequencies devoid of EP and pseudo-inductance polarizations, is the one of interest, as the complex conductivity of the system is there only dependent on material parameters such as the porosity of the sandstone and the conductivity of the electrolyte. We demonstrate that in the bulk region the model predicts the complex conductivity response, when these porosity and ionic strength are known. The model has been validated using laboratory measurements on a Bentheim sandstone saturated with five different NaCl concentrations: 5 mM, 10 mM, 100 mM, 170 mM and 540 mM.

【 授权许可】

CC BY