On Permeability Prediction From Complex Conductivity Measurements Using Polarization Magnitude and Relaxation Time

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We investigate the complex conductivity behaviour of natural volcanic rocks containing variable amounts of smectite in multi‐salinity experiments. We compare the results with relationships established for sandstones. Considering only samples with little volume of metallic particles, we observe similar and small phase‐angles at low frequency for all samples at all salinities (less than 25 mrad at 1 Hz). Yet, a wide range of cation exchange capacity, porosity and formation factor is covered by the sample set: 0.5–50 meq/100 g, 4–40% and 18–780, respectively. Our results show that, in the absence of metallic particles, the ratio between imaginary conductivity and surface conductivity is significantly lower for altered volcanic rocks than for sandstones and decreases with the smectite content. These observations indicate that an increased smectite content causes more conduction and less polarization, which could be explained by the onset of a continuous conduction pathway throughout connected interfoliar spaces of smectite. Due to this pathway, cations from the pore fluid may penetrate the solid lattice, for example through connected smectite aggregates clogging the fracture network, thus preventing polarization. We also observe that the relationship between imaginary conductivity and surface conductivity, at one salinity or over the whole salinity range, is not more significant than the relationship between the imaginary conductivity and the total real conductivity. Therefore, we suggest that the imaginary conductivity cannot be used to discriminate the contributions from smectite and pore water to the total conductivity of altered volcanic rocks.

Section: Introductionmentioning

confidence: 99%

Influence of smectite and salinity on the imaginary and surface conductivity of volcanic rocks

Levy

Weller

Gibert

2019

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“…() and Robinson et al . (). Ten new samples have been added to the database, seven being samples from the Baharija Formation (Egypt) and three being samples from the Shahejie Formation (China).…”

Section: Methodsmentioning

confidence: 97%

“…Geophysical length scales determined from induced polarization provide a possible solution to this problem (Robinson et al . ).…”

Section: Theorymentioning

confidence: 97%

“…The geophysical length scale that results from the characteristic relaxation time (

τ_{p c}

) is (Robinson et al . )

r_{t} = \sqrt{2 D_{+} τ_{p c}},

where

D_{+}

(m 2 /s) is a diffusion coefficient for the ions at the mineral–fluid interface involved in the polarization. In the most commonly applied SLP model, the diffusion coefficient is related to the effective ionic mobility

β_{+}^{S}

, temperature

T_{b}

, the Boltzmann's constant

k_{b}

and the charge of counter ions in the Stern layer

q_{+}

by the Nernst–Einstein relationship

D_{+} = k_{b} T_{b} β_{+}^{s} / false| q_{+} false|

.…”

Section: Theorymentioning

confidence: 99%

“…a pore radius) required in permeability ( k ) prediction models (Robinson et al . ). A geophysical approach to k estimation could substantially advance subsurface characterization by providing spatially dense information on the distribution of relatively high versus relatively low permeability units.…”

Section: Introductionmentioning

confidence: 97%

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Permeability estimation from induced polarization: an evaluation of geophysical length scales using an effective hydraulic radius concept

Weller

Slater

2019

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Geophysical length scales defined from induced‐polarization measurements can be used in models of permeability (k) prediction. We explore the relative merit of different induced‐polarization parameters as proxies of an effective hydraulic radius (reff) that can be used to predict permeability from a modified Hagen–Poiseuille equation. Whereas geometrical measures of the hydraulic radius are good proxies of reff, the induced‐polarization measures are not well correlated with reff. However, a new proxy of reff that considers both imaginary conductivity and formation factor shows an improved correlation with reff. The resulting model enables a better quality of permeability prediction compared with the other geophysical length scales, but does not reach the predictive quality of the models based on geometrical length scales. The specific polarizability defined when incorporating the effect of the formation factor on imaginary conductivity appears to be independent of pore geometry, indicating that it is the correct parameter representing the role of the surface electrochemistry on the induced‐polarization effect. However, the joint dependence of induced‐polarization measurements on both the pore radius and the tortuosity and porosity of the interconnected pore network is a limitation to the widely explored use of induced‐polarization measurements to isolate surface properties from volumetric properties of the interconnected pore network.

Experimental and numerical analysis of dielectric polarization effects in near‐surface earth materials in the 100 Hz–10 MHz frequency range: First interpretation paths

Tabbagh,

Souffaché,

Jougnot

et al. 2024

SummaryThe recent developments of electromagnetic induction and electrostatic prospection devices dedicated to critical zone surveys in both rural and urban contexts necessitate improving the interpretation of electrical properties through complementary laboratory studies. In a first interpretation step, the various experimental results obtained in the 100 Hz–10 MHz frequency range can be empirically fitted by a simple six‐term formula. It allows the reproduction of the logarithmic decrease of the real component of the effective relative permittivity and its corresponding imaginary component, the part associated with the direct current conductivity, one Cole–Cole relaxation and the real and imaginary components of the high‐frequency relative permittivity. For elucidating physical phenomena contributing to both the logarithmic decrease and the observed Cole–Cole relaxation, we first consider the Maxwell–Wagner–Sillars polarization. Using the method of moments, we establish that this continuous medium approach can reproduce a large range of relaxation characteristics. At the microscopic scale, the possible role of the rotation of the water molecules bound to solid grains is then investigated. In this case, contrary to the Maxwell–Wagner–Sillars approach, the relaxation parameters do not depend on the external medium properties.