Interfacial polarization of disseminated conductive minerals in absence of redox-active species — Part 2: Effective electrical conductivity and dielectric permittivity

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. E159-E176 ◽  
Author(s):  
S. Misra ◽  
C. Torres-Verdín ◽  
A. Revil ◽  
J. Rasmus ◽  
D. Homan
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Permittivity ◽  
Electric Field ◽  
Relative Permittivity ◽  
Effective Conductivity ◽  
Interfacial Polarization ◽  
Surface Conductance ◽  
Frequency Dependent ◽  
Mineral Inclusions ◽  
Effective Electrical Conductivity

Hydrocarbon-bearing conventional formations, mudrock formations, and source-rock formations generally contain clays, pyrite, magnetite, graphitelike carbon, and/or other electrically conductive mineral inclusions. Under redox-inactive conditions, these inclusions give rise to perfectly polarized interfacial polarization (PPIP) when subjected to an external electric field. Effective electrical conductivity and dielectric permittivity of geomaterials containing such inclusions are frequency-dependent properties due to the electric-field-induced interfacial polarization and associated charge relaxation around host-inclusion interfaces. Existing resistivity interpretation techniques do not account for PPIP phenomena, and hence they can lead to inaccurate estimation of water saturation, total organic content, and conductivity of formation water based on subsurface galvanic resistivity, electromagnetic (EM) induction, and EM propagation measurements in the presence of conductive mineral inclusions. In the first paper of our two-part publication series, we derived a mechanistic electrochemical model, the PPIP model, and we validated a coupled model that integrates the PPIP model with a surface-conductance-assisted interfacial polarization (SCAIP) model to quantify the frequency-dependent electrical complex conductivity of geomaterials. We have used the PPIP-SCAIP model to evaluate the dependence of effective complex-valued conductivity of geologic mixtures on (1) frequency, (2) conductivity of the host medium, and (3) material, size, and the shape of inclusions. Notably, we have used the PPIP-SCAIP model to identify rock conditions that give rise to significant differences in effective conductivity and effective relative permittivity of conductive-inclusion-bearing mixtures from those of conductive-inclusion-free homogeneous media. For a mixture containing as low as a 5% volume fraction of disseminated conductive inclusions, the low-frequency effective conductivity of the mixture is in the range of [Formula: see text] to [Formula: see text] with respect to the host conductivity for frequencies between 100 Hz and 100 kHz. Further, the high-frequency effective relative permittivity of that mixture is in the range of [Formula: see text] to [Formula: see text] with respect to the host relative permittivity for frequencies between 100 kHz and 10 MHz.

Interfacial polarization of disseminated conductive minerals in absence of redox-active species — Part 1: Mechanistic model and validation

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. E139-E157 ◽  
Author(s):  
S. Misra ◽  
C. Torres-Verdín ◽  
A. Revil ◽  
J. Rasmus ◽  
D. Homan
Keyword(s):  
Electrical Conductivity ◽  
Mechanistic Model ◽  
Interfacial Polarization ◽  
Active Species ◽  
Surface Conductance ◽  
Electrically Conductive ◽  
Mineral Inclusions ◽  
Redox Active ◽  
Polarization Phenomena ◽  
Complex Valued

Electrically conductive mineral inclusions are commonly present in organic-rich mudrock and source-rock formations such as veins, laminations, rods, grains, flakes, and beds. Laboratory and subsurface electromagnetic (EM) measurements performed on geomaterials containing electrically conductive inclusions generally exhibit frequency dispersion due to interfacial polarization phenomena at host-inclusion interfaces. In the absence of redox-active species, surfaces of electrically conductive mineral inclusions are impermeable to the transport of charge carriers, inhibit the exchange of charges and behave as perfectly polarized (PP) interfaces under the influence of an externally applied EM field. Interfacial polarization phenomena involving charge separation, migration, accumulation/depletion, and relaxation around PP interfaces is referred to as PP interfacial polarization; it influences the magnitude and direction of the electric field and charge carrier migration in the geomaterial. We have developed a mechanistic model to quantify the complex-valued electrical conductivity response of geomaterials containing electrically conductive mineral inclusions, such as pyrite and magnetite, uniformly distributed in a fluid-filled, porous matrix made of nonconductive grains possessing surface conductance, such as silica and clay grains. The model first uses a linear approximation of the Poisson-Nernst-Planck equations of dilute solution theory to determine the induced dipole moment of a single isolated conductive inclusion and that of a single isolated nonconductive grain surrounded by an electrolyte. A consistent effective-medium formulation was then implemented to determine the effective complex-valued electrical conductivity of the geomaterial. Model predictions were in good agreement with laboratory measurements of multifrequency complex-valued electrical conductivity, relaxation time, and chargeability of mixtures containing electrically conductive inclusions.

Effects of material texture and packing density on the interfacial polarization of granular soils

Geophysics ◽  
2021 ◽  
pp. 1-58
Author(s):  
Hang Chen ◽  
Qifei Niu
Keyword(s):  
Electrical Conductivity ◽  
Packing Density ◽  
Characteristic Frequency ◽  
Effective Permittivity ◽  
Scale Up ◽  
Interfacial Polarization ◽  
Granular Soils ◽  
Geologic Materials ◽  
Effective Electrical Conductivity ◽  
Material Texture

Many electrical and electromagnetic (EM) methods operate at MHz frequencies, at which the interfacial polarization occurring at the solid-liquid interface in geologic materials may dominate the electrical signals. To correctly interpret electrical/EM measurements, it is therefore critical to understand how the interfacial polarization influences the effective electrical conductivity and permittivity spectra of geologic materials. We have used pore-scale simulation to study the role of material texture and packing in interfacial polarization in water-saturated granular soils. Synthetic samples with varying material textures and packing densities are prepared with the discrete element method. The effective electrical conductivity and permittivity spectra of these samples are determined by numerically solving the Laplace equation in a representative elementary volume of the samples. The numerical results indicate that the effective permittivity of granular soils increases as the frequency decreases due to the polarizability enhancement from the interfacial polarization. The induced permittivity increment is mainly influenced by the packing state of the samples, increasing with the packing density. Material textures such as the grain shape and size distribution may also affect the permittivity increment, but their effects are less significant. The frequency characterizing the interfacial polarization (i.e., the characteristic frequency) is mainly related to the electrical contrast of the solid and water phases. The model based on the traditional differential effective medium (DEM) theory significantly underestimates the permittivity increment by a factor of more than two and overestimates the characteristic frequency by approximately 1 MHz. These inaccurate predictions are due to the fact that the electrical interactions between neighboring grains are not considered in the DEM theory. A simple empirical equation is suggested to scale up the theoretical depolarization factor of grains entering the DEM theory to account for the interaction of neighboring grains in granular soils.

Analysis of Clustering and Interphase Region Effects on the Electrical Conductivity of Carbon Nanotube-Polymer Nanocomposites via Computational Micromechanics

2008 ◽  
Author(s):  
Gary D. Seidel ◽  
Kelli L. Boehringer ◽  
Dimitris C. Lagoudas
Keyword(s):  
Electrical Conductivity ◽  
Polymer Nanocomposites ◽  
Effective Conductivity ◽  
Interphase Layer ◽  
Finite Element Software ◽  
Interphase Region ◽  
Effective Electrical Conductivity ◽  
Wide Range ◽  
Electrical Conductivities ◽  
Computational Micromechanics

In the present work, computational micromechanics techniques are applied towards predicting the effective electrical conductivities of polymer nanocomposites containing aligned bundles of SWCNTs at wide range of volume fractions. Periodic arrangements of well-dispersed and clustered/bundled SWCNTs are studied using the commercially available finite element software COMSOL Multiphysics 3.4. The volume averaged electric field and electric flux obtained are used to calculate the effective electrical conductivity of nanocomposites in both cases, therefore indicating the influence of clustering on the effective electrical conductivity. In addition, the influence of the presence of an interphase region on the effective electrical conductivity is considered in a parametric study in terms of both interphase thickness and conductivity for both the well dispersed case and for the clustered arrangements. Comparing the well-dispersed case with an interphase layer to the same arrangement without the interphase layer allows for the assessment of the influence of the interphase layer on the effective electrical conductivities, while similar comparisons for the clustered arrangements yield information about the combined effects of clustering and interphase regions. Initial results indicate that there is very little influence of the interphase layer on the effective conductivity prior to what is identified as the interphase percolation concentration, and that there is an appreciable combined effect of clustering in the presence of interphase regions which leads to increases in conductivity larger than the sum of the two effects independently.

Frequency Dependence of Electrorheological (ER) Effect and Its Relationship to Dielectric and Electrical Properties in Ba1-xSrxTiO3 Suspensions

2005 ◽  
Vol 19 (07n09) ◽  
pp. 1443-1448 ◽  
Author(s):  
Yasuhito Misono ◽  
Shoichi Furukawa ◽  
Hitomi Yosinaga ◽  
Junko Sugiyama ◽  
Keishi Negita
Keyword(s):  
Electrical Conductivity ◽  
Electrical Properties ◽  
Dielectric Permittivity ◽  
Field Strength ◽  
Electric Field ◽  
Frequency Dependence ◽  
Applied Electric Field ◽  
Electrode Polarization ◽  
Low Frequencies ◽  
High Frequencies

Varying the electric field strength (E), the ER effect, the dielectric permittivity, and the electrical conductivity were simultaneously measured on the Ba 0.75 Sr 0.25 TiO 3 suspension. It was found that at high E the ER effect increased with the frequency (f), while at low E it once decreased and then increased with increase in f. At high E, the dielectric permittivity at low frequencies was much larger than that at high frequencies, indicating that an electrode polarization was formed as a result of accumulations of ions, which were dissociated from the liquid at high E, near the electrodes. This electrode polarization was further confirmed in the time dependence of the electrical conductivity after the electric field was switched on. From these results it is suggested that the E-dependent frequency dependence of the ER effect may be due to the electrode polarization, which causes larger shielding of the applied electric field at lower f while smaller shielding at higher f.

scholarly journals Structural, Optical and Frequency Dependent Electrical Behaviour of Aluminum Nitride (ALN) Nanopowder

2019 ◽  
Vol 8 (3) ◽  
pp. 7928-7932
Keyword(s):  
Electrical Conductivity ◽  
Particle Size ◽  
Dielectric Permittivity ◽  
Aluminum Nitride ◽  
Loss Tangent ◽  
Raman Shift ◽  
Crystallographic Structure ◽  
Electrical Parameters ◽  
Frequency Dependent ◽  
Relative Loss

Aluminum nitride (AlN) is ceramic material. It has very high thermal and low electrical conductivity. The Variation of Various Electrical Parameters viz. Impedance (Z), Admittance (Y), Dielectric Permittivity ('), Relative Loss (''), Electrical Conductivity (), and Loss Tangent (Tan ) with frequency Dependence of Aluminum Nitride (AlN) Nano powder were studied. Scanning electron microscopy (SEM); Raman Spectroscopy; and X-ray diffraction (XRD) were used to analyse the surfaces and structures of aluminum nirtride nanopowder. It has been found that the particle size is of 36.15 nm and the crystallographic structure is amorphous. The surface morphology of the studied compound has been investigated by Scanning Election Microscopy (SEM) indicating the particles are in nanosize and characteristic range of diameters are in nanoscale. The electrical studies of the studied compound have been examined in order to acquire the electrical parameters (mainly dielectric permittivity, loss, conductivity, loss-tangent, impedance, and admittance). Small rise in the conductivity (with frequency dependent) has been observed due to the decrease in the particle size of the material.it is also observed that the relative permittivity ('), relative loss '') and dissipation factor (Tan ) decreases with increase in frequency. The Raman shift variation with the intensity which shows the peaks of the compound are obtained at 506 cm-1 , 615 cm-1 656 cm-1 , 873 cm-1 , 882 cm-1 , 949 cm-1 , and 974 cm-1 using laser at 785 nm.

Dispersive and directional electrical conductivity and dielectric permittivity of conductive-mineral-bearing samples derived from multifrequency tensor electromagnetic induction measurements

Geophysics ◽  
2017 ◽  
Vol 82 (4) ◽  
pp. D211-D223 ◽  
Author(s):  
Siddharth Misra ◽  
Carlos Torres-Verdín ◽  
Dean Homan ◽  
John Rasmus
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Permittivity ◽  
Glass Bead ◽  
Frequency Dispersion ◽  
Source Rocks ◽  
Relative Dielectric Permittivity ◽  
Electrically Conductive ◽  
Mineral Inclusions ◽  
Em Field ◽  
Graphite Inclusions

Organic-rich mudrocks, hydrocarbon-bearing conventional formations, and source rocks generally contain pyrite, rutile, graphite, graphitic precursors, and other electrically conductive minerals in the form of veins, laminations, flakes, and grains. Under redox-inactive subsurface conditions, when an external electromagnetic (EM) field is applied to geomaterials containing conductive mineral inclusions, ions in pore-filling brine and charge carriers (electrons and holes) in electrically conductive mineral inclusions migrate, accumulate/deplete, and diffuse around impermeable host-inclusion interfaces. These EM-field-induced phenomena are referred to as perfectly polarized interfacial polarization (PPIP) phenomena, and they alter the effective electrical conductivity [Formula: see text] and effective relative dielectric permittivity [Formula: see text] of geomaterials. In addition, the relaxation process associated with such polarization phenomena and the time required to fully develop and dissipate the EM-field-induced polarization gives rise to frequency dispersion of [Formula: see text] and [Formula: see text] of geomaterials containing conductive mineral inclusions. A laboratory-based EM apparatus, referred to as a whole-core EM induction tool, was used to measure the directional, multifrequency EM response of brine-saturated 4 in diameter (10.16 cm diameter), 2 ft long (0.61 m long), glass-bead packs containing uniformly distributed pyrite and graphite inclusions. We then implemented a semianalytic (SA) EM forward model, referred to as the SA model, to compute the [Formula: see text] and [Formula: see text] of these conductive-mineral-bearing glass-bead packs. The estimated [Formula: see text] and [Formula: see text] of conductive-mineral-bearing packs exhibit directional and frequency dispersive characteristics, which can be explained using the theory of PPIP phenomena. Relative variations in [Formula: see text] and [Formula: see text] due to frequency dispersion were as large as [Formula: see text] and [Formula: see text], respectively, between the values estimated at 20 and 260 kHz. Computed values of [Formula: see text] of conductive-mineral-bearing packs were unusually large in the range of 103–106, whereas the corresponding values of [Formula: see text] exhibited strong dependence on volume content, size, and metallic nature of conductive mineral inclusions, brine salinity, and frequency. Furthermore, packs containing uniformly distributed pyrite and graphite inclusions exhibited conductivity and permittivity anisotropy in the range of one to two.

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