Spectral induced polarization measurements on variably saturated sand‐clay mixtures

Abstract

Electrical spectral induced polarization (SIP) measurements are increasingly being used in environmental studies of the saturated zone. To better understand the mechanisms causing polarization and to extend the range of SIP applications to the vadose zone, it is important to investigate how the SIP response is affected by water saturation. Therefore, sand and sand‐clay mixtures were drained in several steps using a novel measurement set‐up allowing SIP measurements with a high accuracy. The measured SIP spectra were interpreted by Debye decomposition, which provided a relaxation time distribution and a chargeability distribution that was converted to a normalized total chargeability. The results showed that the normalized total chargeability of the fully saturated samples increased with increasing clay content due to the larger specific surface area of the clay minerals. Furthermore, normalized total chargeability first increased and then decreased with decreasing saturation for the pure sand and the 5% sand‐clay mixture. The normalized total chargeability values for the 10% and 20% sand‐clay mixtures only decreased with saturation. The peak relaxation time of the sand‐clay mixtures clearly decreased with decreasing saturation. Existing grain‐size based mechanistic models for SIP are not able to explain the observed behaviour and the observed relationship between relaxation time and saturation suggests that model concepts relying on polarization processes in the pore space are warranted to explain the measurements on variably saturated porous media presented here.

Estimation of water retention parameters from nuclear magnetic resonance relaxation time distributions

“…To predict the water retention properties of such models, our investigations indicate that NMR relaxometry measurements at saturation cannot provide enough information. Thus, additional methods will be necessary, for instance, measurements of induced polarization (IP) that can be correlated directly with the pore surface [e.g., Binley et al ., 2005; Revil , 2012; Breede et al ., 2012]. The IP method is therefore expected to be sensitive particularly to the pore throats.…”

An overview of the spectral induced polarization method for near‐surface applications

“…As outlined at the end of the previous section, this statement holds today, although some of the above controls have been further investigated in laboratory studies over the past 15 years, including mainly textural parameters (e.g., Vanhala 1997; Slater and Lesmes 2002; Scott and Barker 2003; Binley et al 2005; Slater et al 2006; Kruschwitz et al 2010; Weller et al 2010a) and permeability (e.g., Börner et al 1996; Slater and Lesmes 2002; Binley et al 2005; Revil and Florsch 2010; Zisser et al 2010a; Koch et al 2011; Revil et al 2012b). More laboratory measurements are particularly needed regarding the effect of chemistry (e.g., Lesmes and Frye 2001; Vaudelet et al 2011; Weller et al 2011), saturation (e.g., Ulrich and Slater 2004; Jougnot et al 2010; Breede et al 2012), temperature (e.g., Binley et al 2010; Zisser et al 2010b; Martinez et al 2012), multiple fluid phases (e.g., Cassiani et al 2009; Schmutz et al 2010; Revil et al 2011) and in addition effective pressure (e.g., Zisser and Nover 2009), grain‐size distribution (e.g., Revil and Florsch 2010), pH (e.g., Skold et al 2011) and the effect of microbial processes (see Atekwana and Slater 2009 for a recent review). Biogeophysics research has determined that SIP is one of the most promising geophysical techniques for detecting the alteration of mineral‐fluid interfaces and pore geometries resulting from microbial growth and biofilm formation (e.g., Abdel Aal et al 2004; Ntarlagiannis et al 2005a; Davis et al 2006; Abdel Aal et al 2009, 2010a,b) as well as biomineralization (e.g., Ntarlagiannis et al 2005b; Williams et al.…”

Spectral Induced Polarization measurements on New Zealand sands ‐ dependence on fluid conductivity

“…At high salinities this is often expressed in terms of a parallel combination of ionic conductivity through the pore fluid and a complex surface conductivity (e.g. Keller and Frischknecht ; Slater ; Weller and Slater ; Zisser et al ) …”

“…There are several mechanisms that have been considered as responsible for surface polarization at frequencies below about 10 kHz. These have recently been discussed by Kemna et al () and include effects associated with the formation of the electrical double layer at the interface between mineral grains and the pore fluid. The form of the phase dependence is believed to be characteristic of the grain size and pore structure of the unconsolidated material and SIP is thus believed to hold potential as a proxy for the hydraulic properties of a material (e.g.…”