Use Of Dielectric Measurements Research Articles

Comparison of different dielectric models to calculate water saturation and estimate textural parameters in partially saturated cores

Accurate estimation of water saturation is central in predicting capillary pressure and relative permeability, under special core analysis in the laboratory. We have explored the use of dielectric measurements at different frequencies to estimate water saturation. In addition to water saturation, dielectric measurements are sensitive to the distribution of water and oil in a porous system, reflected by the apparent cementation factor [Formula: see text], which describes the water phase tortuosity. We have performed an experimental study to benchmark water saturation from dielectric measurements on eight carbonate cores and estimated their cementation exponent [Formula: see text] and saturation exponent [Formula: see text] in Archie’s equation from dielectric data. All cores went through a series of drainage/imbibition steps, creating varying saturations of brine/fluorocarbon. Fluorocarbon was chosen because it is invisible to proton nuclear magnetic resonance (NMR). Therefore,NMR porosity represents only the water-filled porosity and can be used to benchmark dielectric water-filled porosity. Three dielectric models were used for the comparison of the dielectric water-filled porosity with the one from NMR, i.e., the complex refractive index model (CRIM), bimodal model, and Stroud-Milton-De (SMD) model, and very good agreement of 1.5 porosity units on average is found. Despite its simplicity, CRIM predicted well the water-filled porosity in this experiment. However, it cannot provide information about the texture, which is captured by bimodal and SMD models. We also estimated [Formula: see text] and [Formula: see text] based on [Formula: see text] found from bimodal and SMD models, and good agreement with [Formula: see text] from resistivity data was shown. This is the first time to our knowledge that such a rich set of dielectric and NMR measurements was acquired at different saturation stages in a surface laboratory. This study is useful in benchmarking the water saturation from dielectrics, comparing different dielectric models, and demonstrating feasibility of estimating textural parameters.

Effective permittivity of porous media: a critical analysis of the complex refractive index model

ABSTRACTThe availability of reliable constitutive models linking the bulk electric properties of porous media to their inner structure is a key requirement for useful quantitative applications of noninvasive methods. This study focuses on the use of dielectric measurements to monitor fluid saturation changes in porous materials. A number of empirical, semi‐empirical and theoretical relationships currently exists that link the bulk dielectric constant with volumetric water content. One such relationship, named complex refractive index model or Lichteneker‐Rother model has been extensively applied in recent years. Here we first analyse the characteristics of this Lichteneker‐Rother model by means of theoretical considerations. This theoretical analysis indicates that the Lichteneker‐Rother exponent is dependent upon the geometrical properties of the porous structure, as well as the permittivity contrast between the different phases. Pore‐scale modelling and experimental data further support this result. The parameter estimation robustness in presence of synthetic data error is also assessed. This demonstrates that Lichteneker‐Rother parameters cannot, in general, be independently identified on the basis of bulk dielectric constant versus moisture content data.

Repeatability and Reliability of the Tube Suction Test

The tube suction test (TST) was developed in a cooperative effort between the Finnish National Road Administration and the Texas Transportation Institute for assessing the moisture susceptibility of granular base materials. The moisture-susceptibility ranking is based on the mean surface dielectric value of compacted specimens after a 10-day capillary soak in the laboratory. The factors that influence moisture susceptibility are discussed, and the use of dielectric measurements in the TST is explained. The TST protocol is given. The repeatability of the test is then evaluated at three different dielectric values, and statistical techniques are employed to enable estimation of the number of replicate samples required in the TST to achieve specified levels of tolerance and reliability. On the basis of the promising results of the test, the Texas Department of Transportation will begin implementation of the TST statewide during 2001.

Characterisation of dispersion of carbon black in high density polyethylene using dielectric measurements

The use of dielectric measurements as a means of characterising the dispersion of carbon black in high density polyethylene has been investigated. The dispersion of carbon black is an important parameter to quantify because of its significant effect on the electrical properties of the material. Samples were prepared at 26 and 31% carbon black level by compounding on a twin screw extruder using different designs of screw to produce three degrees of mixing: low, medium, and high. Dielectric properties were measured as a function of temperature in the solid phase and through into the melt phase at various frequencies.For a given level of carbon black, and at a fixed temperature, the frequency sensitivity of the alternating current (AC) resistivity was related to the dispersion of the carbon black. The AC resistivity and its frequency sensitivity decreased as the distance between the carbon black aggregates decreased, i.e. the frequency sensitivity decreased as the level of carbon black increased, as the degree of mixing decreased, and at lower measurement temperatures (especially below the melting point as opposed to above it). The frequency sensitivity of the AC resistivity is explained qualitatively in terms of a resistor-capacitor network model. In the manufacturing environment, the frequency sensitivity of the AC resistivity may be used as a practical measure of the dispersion of carbon black in high density polyethylene.

Dielectric and mechanical assessment of water ingress into carbon fibre composite materials

High frequency dielectric measurements (300 kHz–3 GHz) have been used to assess the water uptake by bonded composite resin joint structures. Comparison of exposed and dry joints demonstrated that a correlation exists between changes with time in the dielectric properties of the joints and the extent of water uptake in the matrix as determined gravimetrically. Diffusion of water into the joints is discussed in terms of various models. The changes in mechanical properties as a function of water uptake are reported over an extended period of time. The use of dielectric measurements as a non-destructive examination method for the assessment of water ingress into joint structures is demonstrated.

Identification of stereoisomers based on dielectric studies: dipole moments of chloroalkenes and chlorocumulenes

The use of dielectric measurements to assign molecular configurations was examined with model compounds of the chloroalkane, chloroalkene and chlorocumulene type. A dielectric microcell is described which allows of 0.35 mL samples under exclusion of air. Both benzene and cyclohexane were used as solvents. Different theories of dielectric constant are compared to evaluate dipole moments. Dipole moments are analyzed in terms of bond moments. - The results can be summarized as follows: (i) dielectric measurements are feasible up to 1 M solutions without substantial deviation from linearity; (ii) in general, the dipole moments found in both solvents are similar; the aromatic solvent, however, causes a substantial decrease of the values obtained for chloroalkenes with two bulky substituents at the double bonds; (iii) the ( E) isomers of chloroalkenes exhibit significantly higher dipole moments than the corresponding ( Z) isomers; (iv) isomers of non-chlorinated alkenes or cumulenes with dipole moments below 0.6 D cannot be discriminated dielectrically; (v) on the other hand, if the dipole moments of the compounds exceed 1 D, configurations can be assigned unambiguously on the basis of. dielectrical data even in cases where other approaches fail.

Acquisition and Signal Processing of Ground-Penetrating Radar for Shallow Exploration and Open-Pit Mining

The Australian Mineral Industries Research Association (AMIRA) has sponsored Monash University to investigate the acquisition and signal processing of ground-penetrating radar (GPR) for shallow exploration and open-pit mining. This project had three objectives: (1) to acquire high-quality GPR data sets for shallow exploration and surface mining applications under a variety of geological conditions; (2) to develop signal-processing techniques to enhance radar profiles prior to detailed interpretation; (3) to assess the accuracy of GPR and associated processing techniques through comparisons with independent measurements.Over one hundred kilometres of data were recorded at the various sponsors sites in a wide variety of geological conditions for different economic targets. Several examples are presented to demonstrate:1) the hand-carried and vehicle-towed acquisition techniques,2) target detection at depths down to 25 m,3) the benefits of signal processing for good and poor quality data,4) the use of dielectric measurements, petrophysical modelling and frequency-dependent synthetic radargrams,5) the application of seismic interpretation concepts.The project has demonstrated commercially acceptable rates of GPR data acquisition where the penetration is satisfactory. Some of the unfavourable Australian geological conditions for radar have also been identified. Although signal processing techniques have extended the applicable range of the radar technique, additional hardware enhancements have been identified to improve the commercial application of radar. The next stage is to assess the economic feasibility of radar by comparison with competing techniques such as drilling.

The Dielectric Properties of Various Cotton Varieties

The use of dielectric measurements of cotton fibers as a method of measuring the mass of a fiber bundle would eliminate the tedious and time-consuming manual operation of weighing the fiber bundle. The dielectric properties of various cotton varieties were measured using several measuring frequencies for ranges of fiber moisture content and sample pack ing density. For a fiber moisture content greater than the equilibrium moisture content at 10% RH, it was found that there is a significant variation in the dielectric properties between varieties of cotton. As the fiber moisture content approaches zero, the variation between varieties diminishes. At zero fiber moisture content, the variation between varie ties becomes insignificant. At zero moisture content, it was found that it is possible to use dielectric measurements as a reliable measure of the mass of a fiber bundle.