Effect of changing water salinity on complex conductivity spectra of sandstones

Geophysics ◽  
2011 ◽  
Vol 76 (5) ◽  
pp. F315-F327 ◽  
Author(s):  
Andreas Weller ◽  
Katrin Breede ◽  
Lee Slater ◽  
Sven Nordsiek
Keyword(s):  
Electrical Conductivity ◽  
Relaxation Time ◽  
Pore Space ◽  
Internal Surface ◽  
Imaginary Component ◽  
Fluid Composition ◽  
High Porosity ◽  
Equal Concentration ◽  
Fluid Chemistry ◽  
Average Relaxation Time

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 ([Formula: see text]) of sodium and calcium chloride solutions was gradually increased from 25 mS/m to 2300 mS/m. The expected linear relation between [Formula: see text] and the real component of electrical conductivity ([Formula: see text]) of the saturated samples was observed. The imaginary component ([Formula: see text]) exhibits a steeper increase at lower salinities that flattens at higher salinities. For a glauconitic sandstone and a high porosity Bunter sandstone, [Formula: see text] approaches an asymptotic value at high salinities. Sodium cations result in larger values of [Formula: see text] than calcium cations in solutions of equal concentration. Debye decomposition was used to determine normalized chargeability ([Formula: see text]) and average relaxation time ([Formula: see text]) from spectral data. The behavior of [Formula: see text] is comparable to [Formula: see text] as both parameters measure the polarizability. At lower salinity, the relation between [Formula: see text] and [Formula: see text] approximates a power law with an exponent of [Formula: see text]. The average relaxation time shows only a weak dependence on [Formula: see text]. 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 [Formula: see text]. We observe a consistent maximum polarizability for quartz dominated siliceous material.

Investigating the dielectric properties and low-frequency relaxation process of TlGaSe2 crystals

2017 ◽  
Vol 31 (12) ◽  
pp. 1750134 ◽  
Author(s):  
Oktay Samadov ◽  
Oktay Alakbarov ◽  
Arzu Najafov ◽  
Samir Samadov ◽  
Nizami Mehdiyev ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Relaxation Time ◽  
Constant Electric Field ◽  
Low Frequency ◽  
Constant Field ◽  
Impedance Spectra ◽  
Ionic Contribution ◽  
Frequency Relaxation ◽  
Average Relaxation Time ◽  
Diagram Analysis

The dielectric and impedance spectra of TlGaSe2 crystals have been studied at temperatures in the 100–500 K range in the alternating current (AC [Formula: see text]1 V). It has been shown that the conductivity of TlGaSe2 crystals is mainly an ionic characteristic at temperatures above 400 K. The well-defined peak at the frequency dependence of the imaginary part of impedance [Formula: see text] is observed in the 215–500 K temperature range. In a constant field, there occurs a significant decrease in electrical conductivity [Formula: see text] in due course. The ionic contribution to conductivity (76% at [Formula: see text]) has been estimated from a kinetic change in electrical conductivity [Formula: see text] under the influence of a constant electric field. The diagram analysis in a complex plane [Formula: see text] has been conducted by applying the method of an equivalent circuit of the substation. It has been determined that the average relaxation time of the electric module of the sample is [Formula: see text].

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.

Permeability-porosity transforms from small sandstone fragments

Geophysics ◽  
2006 ◽  
Vol 71 (1) ◽  
pp. N11-N19 ◽  
Author(s):  
Ayako Kameda ◽  
Jack Dvorkin ◽  
Youngseuk Keehm ◽  
Amos Nur ◽  
William Bosl
Keyword(s):  
Pore Space ◽  
Petroleum Industry ◽  
Rock Physics ◽  
Three Dimensions ◽  
Absolute Permeability ◽  
High Porosity ◽  
Drill Cuttings ◽  
Thin Sections ◽  
Numerical Experimentation ◽  
The Absolute

Numerical simulation of laboratory experiments on rocks, or digital rock physics, is an emerging field that may eventually benefit the petroleum industry. For numerical experimentation to find its way into the mainstream, it must be practical and easily repeatable — i.e., implemented on standard hardware and in real time. This condition reduces the size of a digital sample to just a few grains across. Also, small physical fragments of rock, such as cuttings, may be the only material available to produce digital images. Will the results be meaningful for a larger rock volume? To address this question, we use a number of natural and artificial medium- to high-porosity, well-sorted sandstones. The 3D microtomography volumes are obtained from each physical sample. Then, analogous to making thin sections of drill cuttings, we select a large number of small 2D slices from a 3D scan. As a result, a single physical sample produces hundreds of 2D virtual-drill-cuttings images. Corresponding 3D pore-space realizations are generated statistically from these 2D images; fluid flow is simulated in three dimensions, and the absolute permeability is computed. The results show that small fragments of medium– to high-porosity sandstones that are statistically subrepresentative of a larger sample will not yield the exact porosity and permeability of the sample. However, a significant number of small fragments will yield a site-specific permeability-porosity trend that can then be used to estimate the absolute permeability from independent porosity data obtained in the well or inferred from seismic techniques.

Predicted Liquid Water Saturation in Unstructured Pore Networks Based on PEMFC GDL Porosity Profiles

2010 ◽  
Author(s):  
J. Hinebaugh ◽  
Z. Fishman ◽  
A. Bazylak
Keyword(s):  
Liquid Water ◽  
Water Saturation ◽  
Pore Space ◽  
Polymer Electrolyte Membrane ◽  
Gas Diffusion ◽  
Pore Network Model ◽  
High Porosity ◽  
Pore Networks ◽  
Electrolyte Membrane ◽  
Capillary Pressures

An unstructured, two-dimensional pore network model is employed to describe the effect of through-plane porosity profiles on liquid water saturation within the gas diffusion layer (GDL) of the polymer electrolyte membrane fuel cell. Random fibre placements are based on the porosity profiles of six commercially available GDL materials recently obtained through x-ray computed tomography experiments. The pore space is characterized with a Voronoi diagram, and invasion percolation-based simulations are performed. It is shown that water tends to accumulate in regions of relatively high porosity due to the lower associated capillary pressures. It is predicted that GDLs tailored to have smooth porosity profiles will have fewer pockets of high saturation levels within the bulk of the material.

scholarly journals The surface CO2 gradient and pore-space storage flux in a high-porosity litter layer

Tellus B ◽  
2004 ◽  
Vol 56 (4) ◽  
pp. 312-321 ◽  
Author(s):  
Adam I. Hirsch ◽  
Susan E.: Trumbore ◽  
Michael L. Goulden
Keyword(s):  
Pore Space ◽  
High Porosity ◽  
Litter Layer ◽  
Storage Flux

Electrical Conductivity Measurements of Al-Doped ZnO Semiconductor in High Temperature

2018 ◽  
Vol 772 ◽  
pp. 105-109
Author(s):  
Syamsul Hadi ◽  
Husein Jaya Andika ◽  
Agus Kurniawan ◽  
Suyitno
Keyword(s):  
Electrical Conductivity ◽  
Temperature Effects ◽  
Sintering Temperature ◽  
High Porosity ◽  
Conductivity Measurements ◽  
Grain Sizes ◽  
Lower Porosity ◽  
Doped Zno ◽  
Zno Semiconductor ◽  
Zno Doping

Electrical conductivity plays an important role in the performance of thermoelectric semiconductor material. This study discusses the electrical conductivity measurements of Zinc Oxide (ZnO) doping Aluminium (Al) pellet as a material of thermoelectric using four-point probe method at high temperatures. Al-doped ZnO (2 wt%) pellet was sintered at the temperature of 1100°C, 1200°C, 1300°C, 1400°C, and 1500°C with the heating rate of 8°C/minute. SEM and XRD tests show that the higher sintering temperature effects to larger grain sizes, better crystallinity, and lower porosity. There is no electrical conductivity in the sintering sample at 1100°C due to the small grain sizes and high porosity. In the sintering sample at 1500°C, the phase of ZnAl2O4erupted. The highest electrical conductivity of 5923.48S/m of Al-doped ZnO pellet was obtained at the sintering temperature of 1400°C with measurement temperature of 500°C.

scholarly journals A New Analytical Expression for the T.C.R. of Thin Monocrystalline Metal Films

1979 ◽  
Vol 5 (4) ◽  
pp. 209-213 ◽  
Author(s):  
C. R. Tellier
Keyword(s):  
Electrical Conductivity ◽  
Relaxation Time ◽  
Reflection Coefficient ◽  
Grain Boundary ◽  
Metal Film ◽  
Approximate Equation ◽  
Metal Films ◽  
Exact Equation ◽  
Temperature Coefficient Of Resistivity ◽  
Comparison Of The Results

The analysis of electrical conductivity of continuous thin monocrystalline metal film has been treated by assuming that the scattering from other sources than grain-boundaries can be described by an effective relaxation time. This relaxation time method is applied to the temperature coefficient of resistivity and leads to an analytical approximate equation in terms of the grain-boundary reflection coefficientrand the reduced thicknessk.Comparison of the results with those deduced from the exact equation (derived from the Mayadas and Shatzkes theory) shows that they deviate by less than 5% in largek–,p–, andr– ranges.

scholarly journals Theoretical Description of Carbon Felt Electrical Properties Affected by Compression

2019 ◽  
Vol 9 (19) ◽  
pp. 4030 ◽  
Author(s):  
Moshe Averbukh ◽  
Svetlana Lugovskoy
Keyword(s):  
Electrical Conductivity ◽  
Electrical Properties ◽  
Close Contact ◽  
Internal Surface ◽  
Theoretical Models ◽  
Theoretical Description ◽  
Carbon Felt ◽  
Long Carbon Fibers ◽  
Carbon Filaments ◽  
The Impact

Electro-conductive carbon felt (CF) material is composed by bonding together different lengths of carbon filaments resulting in a porous structure with a significant internal surface that facilitates enhanced electrochemical reactions. Owing to its excellent electrical properties, CF is found in numerous electrochemical applications, such as electrodes in redox flow batteries, fuel cells, and electrochemical desalination apparatus. CF electro-conductivity mostly arises from the close contact between the surface of two electrodes and the long carbon fibers located between them. Electrical conductivity can be improved by a moderate pressing of the CF between conducting electrodes. There exist large amounts of experimental data regarding CF electro-conductivity. However, there is a lack of analytical theoretical models explaining the CF electrical characteristics and the effects of compression. Moreover, CF electrodes in electrochemical cells are immersed in different electrolytes that affect the interconnections of fibers and their contacts with electrodes, which in turn influence conductivity. In this paper, we investigated both the role of CF compression, as well as the impact of electrolyte characteristics on electro-conductivity. The article presents results of measurements, mathematical analysis of CF electrical properties, and a theoretical analytical explanation of the CF electrical conductivity which was done by a stochastic description of carbon filaments disposition inside a CF frame.

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