Effect of changing water salinity on complex conductivity spectra of sandstones

Abstract

We analyzed the influence of pore fluid composition on the complex electrical conductivity of three sandstones with differing porosity and permeability. The fluid electrical conductivity (σ w ) of sodium and calcium chloride solutions was gradually increased from 25 mS/m to 2300 mS/m. The expected linear relation between σ w and the real component of electrical conductivity (σ 0 ) of the saturated samples was observed. The imaginary component (σ 0 0 ) exhibits a steeper increase at lower salinities that flattens at higher salinities. For a glauconitic sandstone and a high porosity Bunter sandstone, σ 0 0 approaches an asymptotic value at high salinities. Sodium cations result in larger values of σ 0 0 than calcium cations in solutions of equal concentration. Debye decomposition was used to determine normalized chargeability (m n ) and average relaxation time (τ) from spectral data. The behavior of σ 0 0 is comparable to m n as both parameters measure the polarizability. At lower salinity, the relation between m n and σ w approximates a power law with an exponent of ∼0.5. The average relaxation time shows only a weak dependence on σ w . The normalized chargeability of sandstone samples can be described by the product of the pore space related internal surface and a quantity characterizing the polarizability of the mineral-fluid interface that depends on fluid chemistry. We introduce a new parameter, the specific polarizability, describing this dependence. We propose relations between polarizability and fluid chemistry that could be used to estimate pore space internal surface across samples of varying σ w . We observe a consistent maximum polarizability for quartz dominated siliceous material.

On the pore water chemistry effect on spectral induced polarization measurements in the presence of pyrite

“…representing the global polarization magnitude (in contrast to σ″ that represents the polarization magnitude at a single frequency) (Weller et al, 2011). Both σ″ and m nor isolate the polarization effects from conduction effects.…”

Geochemical and geophysical responses during the infiltration of fresh water into the contaminated saprolite of the Oak Ridge Integrated Field Research Challenge site, Tennessee

“…Induced polarization has a long history of use in colloidal chemistry and geophysics, and various petrophysical models have been developed over time to determine the relationship between the in-phase and quadrature conductivities and the texture of the material as well as the electrochemical properties of the mineral water interface [de Lima and Sharma, 1992;Grosse, 2011]. Recent work has focused on the development of a new model based on the polarization of the Stern layer to describe spectral induced polarization of clayey materials with simple supporting electrolytes (e.g., NaCl or KCl) [Revil and Florsch, 2010;Weller et al, 2011;Revil, 2012Revil, , 2013Revil et al, 2013aRevil et al, , 2013c.…”

Subsurface imaging of water electrical conductivity, hydraulic permeability and lithology at contaminated sites by induced polarization

“…As an alternative approach, non-invasive geophysical 61 methods can be used in combination with drillings for improved 3D characterization of 62 contaminant plumes. 63 ′ determined from multisalinity resistivity measurements and Furthermore, Weller et al (2013) found that the salinity dependency of the real surface 146 conductivity parallels the salinity dependency of the imaginary surface conductivity, which can be 147 expressed as (Weller et al, 2011;Weller et al, 2015): 148 where * is the complex conductivity, 0 is the DC conductivity, 0 is the intrinsic chargeability, 182 is the relaxation time, is the frequency exponent, is the frequency and is the imaginary 183 unit. Using MCMC (Monte Carlo Markov Chain) analysis, Fiandaca et al (2017a) (Fig.…”