Complex Refractive Index Method Research Articles

A rapid detection method for diesel content in diesel-contaminated soil based on dielectric measurement and oven-drying tests

Geophysical testing techniques have been successfully applied to identify light non-aqueous phase liquids in soils, but challenges remain in rapidly detecting contaminant content. Detection of contaminants in soil using geophysical testing techniques relies on sensors sensitive to electrical and electromagnetic parameter changes. In this study, the complex permittivity of silty clay contaminated with 0# diesel was measured using an open-ended coaxial probe at frequencies from 200–3000 MHz, and the four-phase dielectric mixing models were evaluated. The measurement results showed that the complex refractive index method (CRIM) model provided a better match with the real permittivity of the four-phase system between 500–3000 MHz with relative errors within an acceptable range of 4%. To eliminate the unknown variable in the CRIM model, an improved equation for the relationship between water content and diesel content of the watery diesel-contaminated silty clay was established by the oven-drying method. Thus, a method for the rapid quantitative detection of the diesel content in contaminated soil has been developed based on dielectric measurement and oven-drying tests. The relative error between the calculated and actual set diesel content for ten manually configured diesel-contaminated soil samples was within 10%, with a maximum error of 15.75%.

Revised models for evaluating hydrocarbon saturation of tight sandstone formations based on dielectric dispersion logs

AbstractAccurate estimation of hydrocarbon saturation is significant for log interpreters to evaluate tight sandstone formations. It is difficult to use conventional wireline logs to calculate hydrocarbon saturation in complex reservoirs. Dielectric dispersion logs are processed using dielectric models to obtain accurate saturation assessment, especially in high salinity shaly sand formations. However, the dielectric models consist of complex refractive index method model and shaly sand model ignore the impact of clay effects on complex refractive index method model, and the dielectric dispersion logs generated by them appear several unphysical phenomena in the clay‐bearing formations, such as the permittivity data at the highest frequency are greater than those at the second highest frequency and the conductivity data at the highest frequency are lower than those at the second highest frequency. This paper modifies the dielectric models by introducing a combined conductive phase in complex refractive index method model to correct the unphysical behaviours. Revised models are combined with four permittivity and four conductivity logs acquired by dielectric scanner at 24, 102, 360 and 960 MHz to inverse the water saturation, water salinity, textural index for water‐bearing pore and fraction of clay‐related phase. The complex refractive index method model interprets the logs measured at 960 MHz and shaly‐sand model interprets other dielectric dispersion logs. The particle swarm optimization algorithm is used to search inversion parameters. The results of forward simulation show that the revised models can correct unphysical behaviours of dielectric dispersion logs generated by the original models. Moreover, we apply original models and revised models to laboratory core data. The results of experiments show that the mean relative error values of the original models are 19.38% and 23.60% and of the revised models are 5.54% and 6.28% in two cases. It shows that the revised models are more accurate than the original models to interpret dielectric dispersion logs of tight sandstone reservoirs.

Theoretical Derivation of and Experimental Investigations into the Dielectric Properties Modeling of Concrete

Investigations into the dielectric properties of concrete form the basis for concrete quality testing and condition monitoring of internal structures when using ground penetrating radar (GPR). The formula used to describe the quantitative relationship between the dielectric properties of composite materials and the dielectric constant and volumetric ratio of each component is known as a dielectric model. In this study, a new dielectric model was deduced from circuit theory on the basis of structural abstraction to calculate the dielectric permittivities of concrete. To validate the applicability and accuracy of the proposed model, because concrete consists of matrix (cement mortar), aggregates (limestone), and air, the dielectric traits of concrete and its components were acquired using an open-ended coaxial probe. Compared with the Brown model, complex refractive index method (CRIM) model, Looyenga model, and Rayleigh model (i.e., the classical models), the results showed that among overall predictions of concrete dielectric constants, the proposed model has the greatest accuracy, because the theoretical results matched the test results more closely. This indicates that the proposed model can better interpret the dielectric properties of concrete, which lays the groundwork for future research into the application of GPR to the nondestructive testing and evaluation of concrete pavement.

Active Layer and Permafrost Investigations Using Geophysical and Geocryological Methods—A Case Study of the Khanovey Area, Near Vorkuta, in the NE European Russian Arctic

Permafrost in the NE European Russian Arctic is suffering from some of the highest degradation rates in the world. The rising mean annual air temperature causes warming permafrost, the increase in the active layer thickness (ALT), and the reduction of the permafrost extent. These phenomena represent a serious risk for infrastructures and human activities. ALT characterization is important to estimate the degree of permafrost degradation. We used a multidisciplinary approach to investigate the ALT distribution in the Khanovey railway station area (close to Vorkuta, Arctic Russia), where thaw subsidence leads to railroad vertical deformations up to 2.5 cm/year. Geocryological surveys, including vegetation analysis and underground temperature measurements, together with the faster and less invasive electrical resistivity tomography (ERT) geophysical method, were used to investigate the frozen/unfrozen ground settings between the railroad and the Vorkuta River. Borehole stratigraphy and landscape microzonation indicated a massive prevalence of clay and silty clay sediments at shallow depths in this area. The complex refractive index method (CRIM) was used to integrate and quantitatively validate the results. The data analysis showed landscape heterogeneity and maximum ALT and permafrost thickness values of about 7 and 50 m, respectively. The active layer was characterized by resistivity values ranging from about 30 to 100 Ωm, whereas the underlying permafrost resistivity exceeded 200 Ωm, up to a maximum of about 10 kΩm. In the active layer, there was a coexistence of frozen and unfrozen unconsolidated sediments, where the ice content estimated using the CRIM ranged from about 0.3 – 0.4 to 0.9. Moreover, the transition zone between the active layer base and the permafrost table, whose resistivity values ranged from 100 to 200 Ωm for this kind of sediments, showed ice contents ranging from 0.9 to 1.0. Taliks were present in some depressions of the study area, characterized by minimum resistivity values lower than 10 Ωm. This thermokarst activity was more active close to the railroad because of the absence of insulating vegetation. This study contributes to better understanding of the spatial variability of cryological conditions, and the result is helpful in addressing engineering solutions for the stability of the railway.

Integrated Dielectric Model for Unconsolidated Porous Media Containing Hydrate

This article reports a novel dielectric model developed for estimating the complex permittivity of unconsolidated porous media containing gas hydrate. The complex permittivity spectra were experimentally obtained by using open-ended-coaxial-probes over a frequency range between 1 MHz and 3 GHz, in which the dielectric dispersion of both hydrate and liquid solution are covered. With tetrahydrofuran used as the hydrate former, reflection coefficients were recorded during the hydrate formation and dissociation processes in quartz sands and the complex permittivity spectra were inversed. Volumetric fractions estimated from the X-ray-tomography were used as the referenced values. Experimental data showed that the Maxwell-Wagner effect, surface conductance, and phase configuration can affect the bulk permittivity. The discrepancy was found to be unacceptable when the fitting was conducted with pre-existing models such as complex-refractive-index-method (CRIM) and Maxwell-Wagner-Bruggeman-Hanai (MWBH). In this study, by modifying the nested Wagner's theory, a shell-coated model was applied, and the surface of the solid sphere was assumed to possess surface conductance when it was humidified by the liquid solution. In contrast to CRIM and MWBH, the proposed model allows more accurate estimation of the volumetric fraction. By adopting this model with a range of dielectric measurements with different phase configurations, temperature, particle size, surface conductivity, and frequency, the contents of components and their influences onto the bulk permittivity can be physically estimated. The proposed model provides an essential tool for the interpretation of dielectric dispersion curves and the prediction of the volumetric fractions, which can be useful for both the field and laboratory applications.

Experimental Study on the Dielectric Model of Common Asphalt Pavement Surface Materials Based on the L-R Model

The establishment of a dielectric model of the asphalt pavement surface material is the premise and key to applying the electromagnetic wave technology to asphalt pavement nondestructive testing. Asphalt pavement can be made of different materials, including various types of asphalt mixtures. Therefore, in order to study and analyze the dielectric properties of different types of asphalt mixtures and establish a dielectric model of the asphalt pavement surface material, this paper studies four types of asphalt mixtures commonly used in the asphalt pavement surface course. Based on the comparative analysis of three classical models, the complex refractive index method (CRIM), Brown, and Looyenga; based on the L-R model, the linear regression analysis was conducted on the test data. The dielectric models which are suitable for the interpretation of four types of asphalt mixtures were established, and the dielectric model database of asphalt pavement surface materials was extended, which provides theoretical and technical support for nondestructive testing of the asphalt pavement.

Complex Electrical Resistivity and Dielectric Permittivity Responses to Dense Non-aqueous Phase Liquids' Imbibition and Drainage in Porous Media: A Laboratory Study

The effective techniques for remediation of sites polluted by dense non-aqueous phase liquids (DNAPLs) remains a challenge. Among the various technical monitoring methods, there is an increasing interest in studying the geophysical characteristics of contaminated soils, as indicators of the progress in clean-up programs. This work sought to investigate the variation of the electrical complex resistivity and the relative permittivity by analyzing the results obtained from spectral induced polarization (SIP) and time domain reflectometry (TDR). Different series of measurements during drainage and imbibition of DNAPLs in porous media were done to validate the clean-up process on sites polluted by DNAPLs. Therefore, a methodology based on laboratory work was designed and carried out to study the electrical complex resistivity (both in magnitude and phase) in the frequency range 0.183 Hz to 20 kHz, and the relative dielectric permittivity at 70 MHz. The experiments were done on small 1D cells. In these cells, glass beads were used as a porous medium. Two different fluid couples, i.e., coal tar (CT)/water and canola oil (CO)/salty ethanol (SE), were used to produce two-phase flow. Our findings highlight that due to the high resistivity of CO and CT, an increase in water saturation led to decrease in amplitude and phase. Saturation change of SE had the same effect on resistivity but no relationship was found for phase and saturation for the mixture CO and SE. It is also showed that the complex resistivity and relative permittivity measurements were compatible with generalized Archie's law and complete complex refractive index method (CRIM) model as two empirical models for defining the correlation between the electrical resistivity, relative permittivity, and saturation of each phase in the multiphase porous medium.

A novel heterogeneous model of concrete for numerical modelling of ground penetrating radar

The ground penetrating radar (GPR) method has increasingly been applied in the non-destructive testing of reinforced concrete structures. The most common approach to the modelling of radar waves is to consider concrete as a homogeneous material. This paper proposes a novel, heterogeneous, numerical model of concrete for exhaustive interpretation of GPR data. An algorithm for determining the substitute values of the material constants of concrete is developed, based on the modified complex refractive index method. Experimental surveys and numerical simulations are conducted on a concrete laboratory sample with a controlled degree of saturation, and on a real concrete slab with two different degrees of saturation. The results indicate that the proposed model is fully capable of realistic finite-difference time-domain modelling of concrete for ground penetrating radar diagnostics of civil engineering structures with changing water content.

Methods for estimating petrophysical parameters from well logs in tight oil reservoirs: a case study

Estimating petrophysical parameters from well logs plays a significant role in the exploration and development of tight oil resources, but faces challenges. What’s more, the methods for petrophysical parameters from well logs are paid little attention at present. In this paper, the typical tight oil reservoirs of Northwest China are used as an example. Based on the characteristics of mineralogy and fluids in the study field, the rock is assumed into five components which are clays, quartz and feldspar, carbonates, kerogen and pore fluids (porosity). The sum of kerogen content and porosity is defined as the apparent porosity. Then, two porosity log response equations are established. Once the clay content is determined by an individual method, the quartz and feldspar content, carbonate content and apparent porosity are calculated through the established equations. The kerogen content is the difference of the apparent porosity and porosity from nuclear magnetic resonance (NMR) logs. This paper also presents a new approach that combines the complex refractive index method (CRIM) and pseudo Archie method to compute saturation from dielectric logs, which avoids selection for the dielectric constants of each of the minerals. The effectiveness and reliability of these methods are verified by the successful application in the study of the target tight oil play in Northwest China.

Hydrodynamic parameters of a sandy soil determined by ground‐penetrating radar inside a single ring infiltrometer

AbstractThis study shows how Mualem‐van Genuchten (M‐vG) parameters can be obtained from GPR data acquired during water infiltration from a single ring infiltrometer in the case of a sandy soil. Water content profiles were generated at various time steps using HYDRUS‐1D, based on particular values of the M‐vG parameters and were converted to dielectric permittivity profiles using the Complex Refractive Index Method. The GprMax suite of programs was used to generate radargrams and to follow the wetting front progression in depth using the arrival time of the electromagnetic waves recorded by a ground‐penetrating radar (GPR). Theoretically, the 1‐D time convolution between reflectivity and GPR signal at any infiltration time step is related to the peak of the reflected signal recorded in the corresponding trace in the radargram. We used this relationship to invert the M‐vG parameters for constant and falling head infiltrations using the Shuffled Complex Evolution (SCE‐UA) algorithm. The method is presented on synthetic examples and on experiments carried out for a sandy soil. The parameters inverted are compared with values obtained in laboratory on soil samples and with disk infiltrometer measurements.

The dielectric permittivity of terrestrial ground ice formations: Considerations for planetary exploration using ground‐penetrating radar

Exploration of the polar ice caps and apparent glacial and periglacial landforms on Mars will aid our understanding of its ancient climate conditions and the history of water on the planet. Given that ground‐penetrating radar (GPR) is likely to be used to understand these features, we investigated the real component of the complex dielectric permittivity of stratified segregation ice, non‐stratified segregation ice, and polygonal ice wedge deposits in the Canadian Arctic. We acquired moveout profiles with a 450 MHz GPR on ground ice formations that had active layer sediments excavated prior to surveying. Using ice core data collected from these sites, we found that the volumetric fraction of ice plays the greatest role in defining the dielectric permittivity of the deposit and that it can be described using a modified complex refractive index method (CRIM) dielectric mixing model. Using the modified CRIM model, we estimate the dielectric permittivity of several ground ice deposits on Earth and present further estimates for similar features on Mars using permittivity values for Martian sediments derived from both theory and laboratory methods.

Georadar‐derived estimates of firn density in the percolation zone, western Greenland ice sheet

Greater understanding of variations in firn densification is needed to distinguish between dynamic and melt‐driven elevation changes on the Greenland ice sheet. This is especially true in Greenland's percolation zone, where firn density profiles are poorly documented because few ice cores are extracted in regions with surface melt. We used georadar to investigate firn density variations with depth along a ∼70 km transect through a portion of the accumulation area in western Greenland that partially melts. We estimated electromagnetic wave velocity by inverting reflection traveltimes picked from common midpoint gathers. We followed a procedure designed to find the simplest velocity versus depth model that describes the data within estimated uncertainty. On the basis of the velocities, we estimated 13 depth‐density profiles of the upper 80 m using a petrophysical model based on the complex refractive index method equation. At the highest elevation site, our density profile is consistent with nearby core data acquired in the same year. Our profiles at the six highest elevation sites match an empirically based densification model for dry firn, indicating relatively minor amounts of water infiltration and densification by melt and refreeze in this higher region of the percolation zone. At the four lowest elevation sites our profiles reach ice densities at substantially shallower depths, implying considerable meltwater infiltration and ice layer development in this lower region of the percolation zone. The separation between these two regions is 8 km and spans 60 m of elevation, which suggests that the balance between dry‐firn and melt‐induced densification processes is sensitive to minor changes in melt.

Estimating porosity with ground‐penetrating radar reflection tomography: A controlled 3‐D experiment at the Boise Hydrogeophysical Research Site

To evaluate the uncertainty of water‐saturated sediment velocity and porosity estimates derived from surface‐based, ground‐penetrating radar reflection tomography, we conducted a controlled field experiment at the Boise Hydrogeophysical Research Site (BHRS). The BHRS is an experimental well field located near Boise, Idaho. The experimental data set consisted of 3‐D multioffset radar acquired on an orthogonal 20 × 30 m surface grid that encompassed a set of 13 boreholes. Experimental control included (1) 1‐D vertical velocity functions determined from traveltime inversion of vertical radar profiles (VRP) and (2) neutron porosity logs. We estimated the porosity distribution in the saturated zone using both the Topp and Complex Refractive Index Method (CRIM) equations and found the CRIM estimates in better agreement with the neutron logs. We found that when averaged over the length of the borehole, surface‐derived velocity measurements were within 5% of the VRP velocities and that the porosity differed from the neutron log by less than 0.05. The uncertainty, however, is scale dependent. We found that the standard deviation of differences between ground‐penetrating‐radar‐derived and neutron‐log‐derived porosity values was as high as 0.06 at an averaging length of 0.25 m but decreased to less than 0.02 at length scale of 11 m. Additionally, we used the 3‐D porosity distribution to identify a relatively high‐porosity anomaly (i.e., local sedimentary body) within a lower‐porosity unit and verified the presence of the anomaly using the neutron porosity logs. Since the reflection tomography approach requires only surface data, it can provide rapid assessment of bulk hydrologic properties, identify meter‐scale anomalies of hydrologic significance, and may provide input for other higher‐resolution measurement methods.

Continuous profiles of electromagnetic wave velocity and water content in glaciers: an example from Bench Glacier, Alaska, USA

AbstractWe conducted two-dimensional continuous multi-offset georadar surveys on Bench Glacier, south-central Alaska, USA, to measure the distribution of englacial water. We acquired data with a multichannel 25 MHz radar system using transmitter–receiver offsets ranging from 5 to 150 m. We towed the radar system at 5–10 kmh–1 with a snow machine with transmitter/receiver positions established by geodetic-grade kinematic differentially corrected GPS (nominal 0.5 m trace spacing). For radar velocity analyses, we employed reflection tomography in the pre-stack depth-migrated domain to attain an estimated 2% velocity uncertainty when averaged over three to five wavelengths. We estimated water content from the velocity structure using the complex refractive index method equation and use a three-phase model (ice, water, air) that accounts for compression of air bubbles as a function of depth. Our analysis produced laterally continuous profiles of glacier water content over several kilometers. These profiles show a laterally variable, stratified velocity structure with a low-water-content (~0–0.5%) shallow layer (~20–30 m) underlain by high-water-content (1–2.5%) ice.

Modelling of GPR waves for lossy media obeying a complex power law of frequency for dielectric permittivity

ABSTRACTThe attenuation of ground‐penetrating radar (GPR) energy in the subsurface decreases and shifts the amplitude spectrum of the radar pulse to lower frequencies (absorption) with increasing traveltime and causes also a distortion of wavelet phase (dispersion). The attenuation is often expressed by the quality factor Q. For GPR studies, Q can be estimated from the ratio of the real part to the imaginary part of the dielectric permittivity.We consider a complex power function of frequency for the dielectric permittivity, and show that this dielectric response corresponds to a frequency‐independent‐Q or simply a constant‐Q model. The phase velocity (dispersion relationship) and the absorption coefficient of electromagnetic waves also obey a frequency power law. This approach is easy to use in the frequency domain and the wave propagation can be described by two parameters only, for example Q and the phase velocity at an arbitrary reference frequency. This simplicity makes it practical for any inversion technique. Furthermore, by using the Hilbert transform relating the velocity and the absorption coefficient (which obeys a frequency power law), we find the same dispersion relationship for the phase velocity. Both approaches are valid for a constant value of Q over a restricted frequency‐bandwidth, and are applicable in a material that is assumed to have no instantaneous dielectric response.Many GPR profiles acquired in a dry aeolian environment have shown a strong reflectivity inside dunes. Changes in water content are believed to be the origin of this reflectivity. We model the radar reflections from the bottom of a dry aeolian dune using the 1D wavelet modelling method. We discuss the choice of the reference wavelet in this modelling approach. A trial‐and‐error match of modelled and observed data was performed to estimate the optimum set of parameters characterizing the materials composing the site. Additionally, by combining the complex refractive index method (CRIM) and/or Topp equations for the bulk permittivity (dielectric constant) of moist sandy soils with a frequency power law for the dielectric response, we introduce them into the expression for the reflection coefficient. Using this method, we can estimate the water content and explain its effect on the reflection coefficient and on wavelet modelling.

Radar frequency dielectric dispersion in sandstone: Implications for determination of moisture and clay content

The relationship between dielectric permittivity, water saturation, and clay content for the Sherwood Sandstone from NE England was characterized as part of a wider study of the vadose zone moisture dynamics and pollution vulnerability of this aquifer. Dielectric permittivity was measured over the full range of saturation levels, for various lithologies ranging from clean medium‐grained sandstone to fine‐grained sandstone containing up to 5% clay, using a specially constructed dielectric cell. Dielectric constant, Kr, is largely independent of frequency between 350 MHz and 1000 MHz. Below 350 MHz, Kr of fine‐grained, clay‐rich sandstone shows frequency dispersion. Tests on physical models of the sandstone consisting of a fine fraction of Ottawa Sand and montmorillonite clay indicate that the clay minerals within the sandstone are responsible for its frequency dispersive behavior. These tests also show that increasing pore fluid salinity increases dielectric dispersion at the lower end of the frequency range, which indicates that this arises from the interfacial Maxwell‐Wagner mechanism associated with platy clay particles. Water saturated sand:clay mixtures show very low dielectric constants at high frequencies (over 650 MHz). This effect is independent of salinity and probably results from the layered geometric arrangement of solids, bound and free water within the swelling clay. The complex refractive index method (CRIM) with a mineral dielectric constant of about 5 provides a good match to the water saturation versus dielectric constant data for all Sherwood Sandstone lithologies at frequencies between 350 and 1000 MHz and for clay‐poor sandstone at lower frequencies. Below 350 MHz the presence of a few percent of clay in some Sherwood Sandstone lithologies raises their CRIM best fit mineral dielectric constant substantially.

Estimation of hydraulic conductivity of an unconfined aquifer using cokriging of GPR and hydrostratigraphic data

Densely sampled geophysical data can supplement hydrogeological data for estimating the spatial distribution of porosity and hydraulic conductivity over an aquifer. A 3D Ground Penetrating Radar (GPR) survey was performed over a shallow unconfined aquifer consisting of a coarse to medium sand sequence overlying an impermeable clay layer. The site is instrumented with piezometers and water levels are frequently monitored. Vertical determination of moisture and granulometry at a resolution of 10 cm were made at a few locations. The GPR reflection times were correlated with piezometric and stratigraphic information; cokriging of both data yields the spatial distribution of the radar velocities within the layers. Porosity and hydraulic conductivities are estimated using the Complex Refractive Index Method (CRIM) and Kozeny–Carman formulations, respectively. A pumping test and a tracer test, both done using a well in the center of the survey zone, provide a measure of the average hydraulic conductivity and its anisotropy. The results from cokriging in the saturated zone show that the estimated parameters agree very well with the measured hydrogeological data. The geometric mean of the porosity is close to the laboratory measurements. The geometric mean of the GPR-derived hydraulic conductivities fits the values obtained from the pumping and tracer tests. The range of estimated hydraulic conductivities is quite large and indicates that flow could be faster or slower than the one predicted from the pumping test in some places. Radar attenuation is also found to be a good indicator of porosity distribution. From the observed (high) GPR attenuations and electrical conductivities of water sampled in the piezometers, porosity is determined using Archie's formula. In the vadose zone, moisture content estimated from the GPR velocities using either CRIM or Topp formulations agree well with the ones from the laboratory measurements. Cokriging of the radar reflection times and of the hydrogeological/stratigraphic data leads to an accurate estimate of the radar velocities with a precision and a spatial resolution much higher than the CDP technique. Within the limits of the interpretative models, porosity, saturation and hydraulic conductivities can accurately be estimated with a high spatial resolution over the survey zone.

Dielectric properties of pyrite samples at 1 100 MHz

Pyrite occurs in many petroleum reservoirs and significantly affects density and electric well logs even in low concentrations. Ultrahigh‐frequency dielectric measurements also are significantly affected by pyrite. Dielectric properties of core samples containing approximately 50 percent pyrite by volume were measured from 800 to 1 200 MHz ([Formula: see text]). These measurements demonstrate the high, complex dielectric permittivity of pyrite and provide data for calculation of pyrite permittivity at ultrahigh frequencies. The measured complex‐permittivity of water‐saturated pyrite nodules is approximately [Formula: see text] at 1 100 MHz and 25 °C. The measured permittivity of pyrite nodules depends upon the concentration of pyrite and only slightly on saturating‐water salinity. Two geometric mixing models, the complex refractive‐index method (CRIM) and a modified Hanai‐Bruggeman‐Sen (HBS) model, are used to analyze the data. CRIM analysis of water‐saturated and oil‐saturated core data gives inconsistent results because the porosity is poorly connected. HBS, with a variable dielectric exponent, provides more consistent results. [Formula: see text] is the complex permittivity of pyrite at 1 100 MHz and 25 °C determined by applying HBS to laboratory measurements. CRIM‐determined pyrite permittivity is about 50 percent greater in both real and imaginary parts. This high [Formula: see text] has important implications for high‐frequency dielectric well‐logging tools. Signal amplitudes are highly attenuated in formations with large concentrations of pyrite. Where pyrite nodules occur, wave scattering may cause inconsistent data indicative of formation heterogeneity. Low concentration, disseminated pyrite increases the rock “matrix” permittivity. Mineralogical variations, particularly in trace quantities of heavy minerals, are a likely explanation for significant variations in measured matrix permittivities for sandstones. Comparison of pyrite permittivity with available values for the permittivity of rutile, another heavy mineral found in sedimentary rocks, suggests employing pyrite and rutile in artificial sandpack experiments. The real parts of pyrite and rutile permittivities are nearly equal, but the imaginary part of the permittivity of rutile is lower than pyrite by about [Formula: see text]. Experiments with both minerals could test mixing models and the effects of distribution in mixtures of conductive minerals.