scholarly journals The dielectric constant of sandstones, 60 kHz to 4 MHz

Geophysics ◽  
1987 ◽  
Vol 52 (5) ◽  
pp. 644-654 ◽  
Author(s):  
Rosemary J. Knight ◽  
Amos Nur
Keyword(s):  
Dielectric Constant ◽  
Surface Area ◽  
Dielectric Response ◽  
Water Saturation ◽  
Pore Space ◽  
Strong Dependence ◽  
Complex Impedance ◽  
Volume Ratio ◽  
Electrode Polarization ◽  
Frequency Range

Complex impedance data were collected for eight sandstones at various levels of water saturation [Formula: see text] in the frequency range of 5 Hz to 4 MHz. The measurements were made using a two‐electrode technique with platinum electrodes sputtered onto the flat faces of disk‐ shaped samples. Presentation of the data in the complex impedance plane shows clear separation of the response due to polarization at the sample‐electrode interface from the bulk sample response. Electrode polarization effects were limited to frequencies of less than 60 kHz, allowing us to study the dielectric constant κ′ of the sandstones in the frequency range of 60 kHz to 4 MHz. κ′ of all samples at all levels of saturation shows a clear power‐law dependence upon frequency. Comparing the data from the eight sandstones at [Formula: see text], the magnitude of the frequency dependence was found to be proportional to the surface area‐to‐volume ratio of the pore space of the sandstones. The surface area‐to‐volume ratio of the pore space of each sandstone was determined using a nitrogen gas adsorption technique and helium porosimetry. κ′ also exhibits a strong dependence on [Formula: see text]. κ′ increases rapidly with [Formula: see text] at low saturations, up to some critical saturation above which κ′ increases more gradually and linearly with [Formula: see text]. Using the surface area‐to‐volume ratios of the sandstones, the critical saturation in the dielectric response was found to correspond to water coverage of approximately 2 nm on the surface of the pore space. Our interpretation of the observed dependence of κ′ on both frequency and [Formula: see text] is that it is the ratio of surface water to bulk water in the pore space of a sandstone that controls the dielectric response through a Maxwell‐Wagner type of mechanism.

The Influence of clay content, salinity, stress, and wettability on the dielectric properties of brine‐saturated rocks: 10 Hz to 10 MHz

Geophysics ◽  
1994 ◽  
Vol 59 (6) ◽  
pp. 909-917 ◽  
Author(s):  
Ali A. Garrouch ◽  
Mukul M. Sharma
Keyword(s):  
Dielectric Constant ◽  
Cation Exchange ◽  
Cation Exchange Capacity ◽  
Volume Fraction ◽  
Pore Space ◽  
Ambient Pressure ◽  
Complex Impedance ◽  
Clay Content ◽  
Exchange Capacity ◽  
Constant Frequency

Complex impedance measurements have been performed on 14 shaly sand samples, Berea sandstone, and Ottawa sand‐bentonite packs in a frequency range of 10 Hz to 10 MHz, using both the two‐ and four‐electrode techniques. Measurements have been conducted at an effective radial stress varying from ambient pressure to 4000 psi for brine‐saturated oil‐wet and water‐wet samples. The dielectric permittivity is found to correlate with the clay volume fraction, the cation exchange capacity, and electrochemical potential of the rock samples and to depend strongly on the salinity of the brine used. Stress and wettability are shown to have a small influence on the dielectric constant of fully brine‐saturated rocks. A lower critical frequency is found to characterize the geometry of the pore space. Empirical correlations between the dielectric constant, frequency, permeability, cation exchange capacity, and porosity are presented for the shaly sands used in this study. These correlations provide a means of estimating important petrophysical parameters such as the permeability and the clay content from a nondestructive complex impedance sweep of shaly sands fully saturated with brine.

A new concept in modeling the dielectric response of sandstones: Defining a wetted rock and bulk water system

Geophysics ◽  
1990 ◽  
Vol 55 (5) ◽  
pp. 586-594 ◽  
Author(s):  
Rosemary Knight ◽  
Anthony Endres
Keyword(s):  
Dielectric Response ◽  
Water Saturation ◽  
Water System ◽  
Theoretical Models ◽  
Bulk Water ◽  
Frequency Range ◽  
Poor Agreement ◽  
Text Data ◽  
Pronounced Increase ◽  
Saturation Region

Experimental data for the real part of the dielectric constant (K′) of three sandstone samples are considered as a function of the level of water saturation [Formula: see text] in the frequency range 60 kHz to 4 MHz. Existing theoretical models have previously shown poor agreement with K′ versus [Formula: see text] data for rock samples, undoubtedly due to the complexity involved in adequately accounting for geometrical and electrochemical effects. In analyzing the data presented here, we find a pronounced increase in K′ in the low saturation region which in all cases can be attributed to the establishment of geometrical and surface effects associated with the rock‐water interface. When this increase in K′ is accounted for by defining wetted matrix parameters, the data show excellent agreement with existing theoretical models.

scholarly journals Morphology-dependent space charge polarization and dielectric relaxation of CdO nanomorphotypes

2016 ◽  
Vol 06 (04) ◽  
pp. 1650030 ◽  
Author(s):  
Paulose Thomas ◽  
K. E. Abraham
Keyword(s):  
Dielectric Constant ◽  
Space Charge ◽  
Dielectric Relaxation ◽  
Cadmium Oxide ◽  
Complex Impedance ◽  
Volume Ratio ◽  
Interfacial Polarization ◽  
Theoretical Models ◽  
Space Charge Polarization ◽  
Dielectric Polarization

A versatile approach signifying the morphology-dependent dielectric polarization and relaxation mechanisms of cadmium oxide (CdO) nanosphere, nanoflakes and nanoparallelepiped morphotypes as a function of frequency and temperature is presented. Variation of dielectric property is observed due to the changes of space charge/interfacial polarization resulting from the variations of surface to volume ratio of nanomorphology. Accordingly, colossal dielectric constant value has been observed in CdO nanosphere having larger surface to volume ratio. The order of dielectric constant (dc) values observed for the present nanomorphologies is: dc of sphere [Formula: see text] dc of flakes [Formula: see text] dc of parallelepiped resembles the order of surface to volume ratios of the present morphologies respectively. The experimental data of complex impedance values are numerically fitted using theoretical models which provide the information of role of grain resistance on dielectric polarization and Cole–Cole type mechanism of dielectric relaxation process. The activation energies for electron transport are found to be 0.087[Formula: see text]eV for spheres, 0.074[Formula: see text]eV for flakes and 0.067 for parallelepiped nanomorphotypes of CdO. The dielectric and impedance spectroscopic analysis of the present material opens up wide scope for morphology-dependent tuning of nanomaterials for electrical applications.

Rock/water interaction in dielectric properties: Experiments with hydrophobic sandstones

Geophysics ◽  
1995 ◽  
Vol 60 (2) ◽  
pp. 431-436 ◽  
Author(s):  
Rosemary Knight ◽  
Ana Abad
Keyword(s):  
Dielectric Constant ◽  
Dielectric Response ◽  
Water Saturation ◽  
Dielectric Behavior ◽  
Partially Saturated ◽  
Water Interaction ◽  
Water Wetting ◽  
Rock Water Interaction ◽  
Air System ◽  
Air Mixing

The dielectric constant of a partially saturated sandstone varies as a function of the level of water saturation. Experimental data indicate that rock/water interaction, at low saturations, has a large effect on the measured dielectric response. To theoretically predict the dielectric constant of the rock/water/air system, this rock/water interaction must be accounted for by including the effect of the water wetting the rock solid. Alternatively, if the rock/water interaction can be eliminated, a three‐component (dry rock, water, and air) mixing law can be used to model the dielectric behavior. In this laboratory study, a chemical treatment is used to change four water‐wet sandstones into hydrophobic sandstones. In three hydrophobic samples the rock/water interaction, seen in the data for the water‐wet samples, is eliminated and the dielectric constant of the partially saturated sandstones can be simply modeled as a dry rock/water/air system. This experimental study illustrates the importance of the chemical state of the rock surfaces in determining the dielectric behavior of sandstones.

Dielectric and impedance spectroscopy of K+-doped MgAl2O4 nanoparticles

2018 ◽  
Vol 32 (15) ◽  
pp. 1850189
Author(s):  
Javed Ahmad ◽  
S. H. Bukhari ◽  
M. Qadeer Awan ◽  
M. Ehsan Mazhar ◽  
A. R. Makhdoom
Keyword(s):  
Dielectric Constant ◽  
Impedance Spectroscopy ◽  
High Frequency ◽  
Dielectric Response ◽  
Room Temperature ◽  
Parent Compound ◽  
Low Frequency ◽  
Space Charge Polarization ◽  
Relaxation Phenomena ◽  
Frequency Range

In this study, the dielectric response of Potassium (K[Formula: see text])-doped magnesium aluminates nanoparticles (Mg[Formula: see text]K[Formula: see text]Al2O4, x = 0.0, 0.25, 0.5, 0.75, 1.0) have been investigated as a function of frequency (20 Hz to 2 MHz) at room-temperature. Interestingly, the behavior of dielectric constant indicated the ionic or space charge polarization in the low-frequency range and it remains almost constant at high frequency. However, the value of conductivity increases at higher frequencies which is consistent with the previously reported results for the parent compound MgAl2O4. Moreover, the Cole–Cole plots represent various relaxation phenomena reflecting the existence of grain (boundaries) resistance effects.

scholarly journals Dielectric properties of Ep\TiO2;Ep\MgO nano composites

2019 ◽  
Vol 14 (31) ◽  
pp. 161-121
Author(s):  
Khadijha S. Mohan
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Volume Ratio ◽  
The State ◽  
Nano Composites ◽  
Frequency Range ◽  
Frequency Increase

The Dielectric properties of EP/TiO2 and MgO nanocomposite ata frequency range of (102-106 Hz) were studied. The composite wereprepared with the state volume ratio (0, 0.05, 0.1) for EP/TiO2 andMgO respectively. The impedance, dielectric constant and dielectricloss were found decrease with frequency increase.

Fabrication and Characterization of Colossal Dielectric Response of Polycrystalline Ca1-x SrxCu3Ti4O12 (0≤x≤1) Ceramics

2012 ◽  
Vol 1454 ◽  
pp. 81-87 ◽  
Author(s):  
Sung Yun Lee ◽  
Duk-Keun Yoo ◽  
Jihye Lee ◽  
William Jo ◽  
Youn-Woo Hong ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Dielectric Response ◽  
Full Range ◽  
Complex Impedance ◽  
Lattice Parameter ◽  
Linear Increase ◽  
Lower Dielectric Constant ◽  
Second Phases ◽  
Fabrication And Characterization

ABSTRACTWe report the microstructures and dielectric properties of Ca1-xSrxCu3Ti4O12 (C1-xSxCTO, 0≤x≤1) ceramics sintered at the various sintering temperatures ranging from 1000 to 1060˚C in air. The linear increase in lattice parameter in C1-xSxCTO (0≤x≤1) ceramics is observable for the full range of substitution. However, the second phases of SrTiO3 and CuO start to occur from the composition of x=0.8, implying that a stoichiometric SrCu3Ti4O12 (SCTO) compound may not exist. While the C0.6S0.4CTO and C0.4S0.6CTiO samples exhibit relatively lower dielectric constant (εr) of ∼40,000 below 1 kHz, the CaCu3Ti4O12 (CCTO) and SCTO show the extremely high εr values of ~120,000 and ∼180,000, respectively. Complex impedance (Z*) and modulus (M*) spectroscopy revealed that the capacitance (C) and resistivity (ρ) values of grain boundary in all samples are much higher than those of grains.

Dielectric and Electrical Studies of PMMA and PVP in Polar Solvents

2013 ◽  
Vol 209 ◽  
pp. 133-136 ◽  
Author(s):  
Dharmishtha Barot ◽  
Deepti Tripathi
Keyword(s):  
Dielectric Constant ◽  
Polar Solvent ◽  
Ionic Conduction ◽  
Polymer Concentration ◽  
Relaxation Times ◽  
Complex Impedance ◽  
Complex Dielectric Constant ◽  
Segmental Motion ◽  
Electrode Polarization ◽  
Low Frequencies

The dielectric and electric properties of poly (methyl Methacrylate) (PMMA) and Poly (vinyl Pyrrolidione) (PVP) in polar solvent have been studied in the frequency range of 20 Hz to 2 MHz at room temperature. The effect of polar solvent environment on the dielectric and electrical parameters such as the complex dielectric constant (Є*), relaxation times complex electrical modulus (M*) and complex impedance (Z*) has been analysed . Dielectric dispersion curves show that the polymer concentration plays an important role in governing its segmental motion in solvent solution. At low frequencies, the ionic conduction and electrode polarization seems to have dominant influence on the large increase of complex dielectric constant values.

Evaluation of Nanotechniques and Conventional Techniques for the Removal of Dioxins

2018 ◽  
Vol 9 (1) ◽  
pp. 79-84
Author(s):  
Vaishali V. Shahare ◽  
Rajni Grover ◽  
Suman Meena
Keyword(s):  
Soil Sample ◽  
Human Health ◽  
Surface Area ◽  
Contaminated Soil ◽  
Conventional Treatment ◽  
Volume Ratio ◽  
Soil Samples ◽  
Dioxins And Furans ◽  
Palladized Iron ◽  
The Impact

Background: The persistent dioxins/furans has caused a worldwide concern as they influence the human health. Recent research indicates that nonmaterial may prove effective in the degradation of Dioxins/furans. The nanomaterials are very reactive owing to their large surface area to volume ratio and large number of reactive sites. However, nanotechnology applications face both the challenges and the opportunities to influence the area of environmental protection. Objective: i) To study the impact of oil mediated UV-irradiations on the removal of 2,3,7,8-TCDD, 2,3,7,8-TCDF, OCDD and OCDF in simulated soil samples. ii) To compare the conventional treatment methods with the modern available nanotechniques for the removal of selected Dioxins/furans from soil samples. Methods: The present work has investigated an opportunity of the degradation of tetra and octachlorinated dioxins and furans by using oil mediated UV radiations with subsequent extraction of respective dioxins/furans from soils. The results have been compared with the available nanotechniques. Results: The dioxin congeners in the simulated soil sample showed decrease in concentration with the increase in the exposure time and intensity of UV radiations. The dechlorination of PCDD/Fs using palladized iron has been found to be effective. Conclusion: Both the conventional methods and nanotechnology have a dramatic impact on the removal of Dioxins/furans in contaminated soil. However, the nanotechniques are comparatively costlier and despite the relatively high rates of PCDDs dechlorination by Pd/nFe, small fraction of the dioxins are recalcitrant to degradation over considerable exposure times.

scholarly journals Estimation of permeability and saturation based on imaginary component of complex resistivity spectra: A laboratory study

2020 ◽  
Vol 12 (1) ◽  
pp. 299-306
Author(s):  
Jiang Jia ◽  
Shizhen Ke ◽  
Junjian Li ◽  
Zhengming Kang ◽  
Xuerui Ma ◽  
...  
Keyword(s):  
Water Saturation ◽  
Pore Space ◽  
Evaluation Model ◽  
Low Frequency ◽  
Petroleum Exploration ◽  
Western China ◽  
Imaginary Component ◽  
Estimation Model ◽  
Complex Resistivity ◽  
Linear Relationships

AbstractLow-frequency resistivity logging plays an important role in the field of petroleum exploration, but the complex resistivity spectrum of rock also contains a large amount of information about reservoir parameters. The complex resistivity spectra of 15 natural sandstone cores from western China, with different water saturations, were measured with an impedance analyzer. The pore space of each core was saturated with NaCl solution, and measurements were collected at a frequency range of 40–15 MHz. The results showed a linear relationship between the real resistivity at 1 kHz and the maximum values of imaginary resistivity for each core with different water saturations. The slopes of the linear best-fit lines had good linear relationships with the porosity and the permeability of cores. Based on this, a permeability estimation model was proposed and tested. In addition, the maxima of imaginary resistivity had power exponential relationships with the porosity and the water saturation of the cores. A saturation evaluation model based on the maxima of imaginary resistivity was established by imitating Archie’s formula. The new models were found to be feasible for determining the permeability and saturation of sandstone based on complex resistivity spectrum measurements. These models advance the application of complex resistivity spectrum in petrophysics.

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