Archie's Law Research Articles

Patterns of electrical properties change of heavy metal-organic compound contaminated media in soil-groundwater systems: From laboratory experiments to site application

Differences in electrical properties of media are the basis for determining the type and extent of contamination using geophysical methods. However, differences in heavy metals and organic matter complicate the electrical properties of compound-contaminated media, and existing geophysical methods cannot independently identify compound contamination. Therefore, this study proposes a geophysical detection system that combines electrical resistance tomography (ERT) and induced polarization methods and establishes a solid theory as the basis for the system application through laboratory experiments, model analysis, and site applications. The study reveals that as the organics volume proportion increases, the resistivity and normalized chargeability of contaminated media increased slowly, followed by a rapid increase, and finally reached a stable state. The specific type of compound significantly influences the electrical properties, while the resistivity of different kinds of compound-contaminated media reaches the same maximum value as the organics volume proportion increases. The medium type determines the contaminated media's lower resistivity limit and upper normalized chargeability limit. Additionally, the interplay between heavy metal type, content, and medium complicates the electrical properties of the media, with the compound type exerting a significant impact on resistivity. Archie's law and random forest modeling reveal that the inflection point for resistivity change occurs at 40 % and 80 % organics volume proportions, while the inflection point for normalized chargeability change occurs at 30 % and 70 % organics volume proportions in compound-contaminated media. These inflection points depend on the types of compounds, compositions, proportions, and media, and their importance for the electrical properties of the media changes with the increasing organics volume proportion. Based on the changing patterns of resistivity and normalized chargeability in heavy metal-organic compound contaminated media, the modified geophysical detection system can effectively identify the pollution type and intensity, which provides accurate pollution information to develop effective treatment strategies.

On the accuracy of saturation estimation from electrical measurements of soils with high swelling clay content

AbstractElectrical conductivity models have been widely used to estimate water content and petrophysical properties of soils in hydrogeophysical studies. However, these models are typically only valid for soils with non‐expandable matrices because they were originally developed for clean sandstone reservoir rocks. Soils containing swelling clays are characterized by matrices that expand/contract upon gaining/losing water. In this laboratory study, we demonstrate that soil matrix changes affect saturation estimation using Archie's laws. A sample of a soil containing a swelling clay was fully saturated with a potassium chloride solution, then left to dry evaporatively at room temperature for 8 days. The complex resistivity of the soil, along with its weight and volume shrinkage, were measured daily during the drying period, and the surface conductivity was calculated based on previous empirical findings. Over the course of the study, the simultaneous evaporation yielded a 33% decrease in volume and caused a nonlinear reduction in saturation with decreasing water content. Accounting for surface conductivity and correcting for saturation using the calculated volume reduction resulted in a power‐law relationship with high R2 values between resistivity and saturation along with reasonable saturation exponents. On the contrary, neglecting either surface conductivity or shrinkage caused similar underestimations of saturation exponents. These results indicate that the application of Archie's second law to soils with swelling clays leads to erroneous predictions of resistivity if saturation values are not corrected for changes in the volume of the soil and surface conductivity is neglected.

Electrical conductivity of antigorite–olivine aggregates under high temperature and pressure: Implications for the water content in mantle wedges

Antigorite–olivine aggregates were synthesized to serve as representative lithologies of subduction zones, which often suffered serpentinization due to the hydration of the mantle wedge. The electrical conductivities (EC) of antigorite–olivine aggregates with different antigorite proportions before and after dehydration at 2.0 GPa were measured. An increase in electrical conductivity prior to antigorite dehydration was due to Fe and Mg interdiffusion with an activation enthalpy of 130–200 kJ/mol. The electrical conductivity of the aggregates increased to 0.1 S/m due to antigorite dehydration. The electrical conductivity of 0.1 S/m derived from the laboratory experiments is consistent with geophysical observations. Combined cube model and modified Archie's law model with previous studies, the volume fractions of aqueous fluids in the mantle wedge of cold and hot subduction zones were estimated.

Prediction of reservoir properties using inverse rock physics modelling in the Kanywataba Exploration Area, Albertine Graben

In this study we used the concept of inverse rock physics modelling to analyse reservoir properties of the Kanywataba Exploration Area, with a focus on their lateral distribution away from the Kanywataba well. The procedure employed rock physics models calibrated for the basin constrained by seismic inversion data, where non-uniqueness and data error propagation issues were also taken into account. Both seismic and well log datasets were used in the data calibration. The procedures enabled us to obtain the most likely estimate mean, weighted mean and posterior mean of the reservoir properties. We obtained a good match between measured and modelled porosity values. Any misfit between the observed and predicted lithology was mainly attributed to uncertainties in defining the correct mineral properties. The integrated approach revealed that high porosities correlate with low clay volumes and, furthermore, indicated two distinct reservoir units in the basin, which were interpreted as the Oluka and Kakara Formations. Fluid saturation data were less successfully predicted but this was most probably due to a result of lack of real saturation logs for use in the calibration of the rock physics model; instead, predicted saturation logs based on Archie's law were used in the calibration process. This analysis is first of its kind in this basin and therefore exhibits a high level of novelty in the determination of reservoir properties in this area.

Electrical resistivity, seismic velocity, and porosity of crustal rocks from the Oman ophiolite under brine-saturated ocean floor conditions

In order to examine the effects of crack properties on electrical resistivity and seismic velocity, we conducted simultaneous measurements of electrical resistivity, seismic velocity and porosity at brine-saturated hydrostatic pressures using mafic crustal rocks from the Oman ophiolite. The resistivity and velocity of the samples increase systematically with increasing confining pressure owing to the closure of cracks, as monitored by changes in porosity. Apparent formation factors of each sample are related to the porosity, but nonlinear relationships on logarithmic plots indicate that Archie's law cannot explain these experimental data. We evaluated the effect of crack porosity and aspect ratio for the measured velocity based on the effective medium theory, and the electrical resistivity was inferred from the crack porosity and connectivity according to the percolation model. The experimental velocity and resistivity results are consistent with the model calculations in terms of crack density, aspect ratio and connectivity. We applied a combined velocity-resistivity model to the geophysical logging and borehole data for the oceanic crust in Hole 504B. Our inversion results indicate that the seismic layer 2/3 transition is primarily caused by an alteration front controlled by interconnected cracks and fluid flow in the oceanic crust.

Pore structure exponent of Archie's law in a dual-porosity medium: Vuggy reservoirs

The porosity exponent (m) is one of the most critical parameters of Archie's equation and plays a significant role in quantitative evaluation of petroleum reservoirs. In vuggy carbonate reservoirs, it is difficult to separately quantify the matrix pores and vugs in natural core samples; consequently, how the matrix pores and vugs influence m remains unclear. In this study, a novel method was developed for preparing artificial vuggy core samples with specific values for matrix and vug porosity. The optimal preparing parameters of vuggy core samples, for the material to be consistent with the porosity and permeability of actual core samples, were as follows: 0.25 mm dolomite particles and 0.18 mm glass beads as the rock skeleton, epoxy resin as the binder, 10 mm sodium thiosulfate to form the vugs (compacted and gasified), a component ratio of 1:3:3, and a compaction pressure of 20 MPa. Next, petrophysical and resistivity experiments were carried out to obtain the m and porosity value of 15 artificial vuggy cores. Based on a comprehensive analysis of the artificial core samples, actual core samples, and porosity model, the response of m to matrix and vug porosity was modeled further. The key results are as follows: (1) the larger the portion of vugs to total porosity (Φv/Φ), the greater the increase in m with a range from 2 to 3.5 was found; (2) with the increases of Φ, m increases first and then decreases, where the inflection point of artificial and actual samples is in the range of Φ≈ 18%–20%; (3) the trend of variation of m with Φ is mainly controlled by Φv/Φ or Φm/Φ rather than Φv or Φm individually. What was revealed in this study, can provide theoretical support for using Archie's equation in carbonate reservoirs.

Modeling of blood flow in cerebral arterial circulation and its dynamic impact on electrical conductivity in a realistic multi-compartment head model

Background and ObjectiveThis study aims to assess the dynamic impact of non-Newtonian cerebral arterial circulation on electrical conductivity within a realistic multi-compartment head model. Evaluating this research question is crucial and challenging due to its relevance to electrophysiological modalities like transcranial electrical stimulation (tES), electro-/magnetoencephalography (EEG/MEG), and electrical impedance tomography (EIT). In these modalities, accurate forward modeling depends on the electrical conductivity, which is affected by complex tortuous vessel networks, limited data acquisition in Magnetic Resonance Imaging (MRI), and non-linear blood flow phenomena, including shear rate and viscosity in non-Newtonian fluid. MethodsTo obtain an approximation for the blood concentration, we first use Navier–Stokes equations (NSEs) to solve for the pressure and velocity of the blood in the major vessels. Then Fick's law is used to solve for the blood concentration in the tissues. Finally, Archie's law is used to estimate the electrical conductivity distribution based on the blood concentration. ResultsThe results, obtained with an open 7 Tesla MRI dataset, suggest that a dynamic model of cerebral blood flow (CBF) for both arterial and microcirculation can be established; we find blood pressure and electrical conductivity distributions given a numerically simulated pulse sequence and approximate the blood concentration and electrical conductivity inside the brain based on those. ConclusionsOur model provides an approximation of the dynamical blood flow and the corresponding electrical conductivity distribution in the different parts of the brain. The advantage of our approach is that it is applicable with limited a priori information about the blood flow and with an arbitrary head model distinguishing the arteries.

Imaging of the electrical activity in the root zone under limited-water-availability stress: a laboratory study for Vitis vinifera

Abstract. Understanding root signals and their consequences for the whole plant physiology is one of the keys to tackling the water-saving challenge in agriculture. The implementation of water-saving irrigation strategies, such as the partial root zone drying (PRD) method, is part of a comprehensive approach to enhance water use efficiency. To reach this goal tools are needed for the evaluation of the root's and soil water dynamics in time and space. In controlled laboratory conditions, using a rhizotron built for geoelectrical tomography imaging, we monitored the spatio-temporal changes in soil electrical resistivity (ER) for more than a month corresponding to eight alternating water inputs cycles. Electrical resistivity tomography (ERT) was complemented with electrical current imaging (ECI) using plant-stem-induced electrical stimulation. To estimate soil water content in the rhizotron during the experiment, we incorporated Archie's law as a constitutive model. We demonstrated that under mild water stress conditions, it is practically impossible to spatially distinguish the limited-water-availability effects using ECI. We evidenced that the current source density spatial distribution varied during the course of the experiment with the transpiration demand but without any significant relationship to the soil water content changes. On the other hand, ERT showed spatial patterns associated with irrigation and, to a lesser degree, to RWU (root water uptake) and hydraulic redistribution. The interpretation of the geoelectrical imaging with respect to root activity was strengthened and correlated with indirect observations of the plant transpiration using a weight monitoring lysimeter and direct observation of the plant leaf gas exchanges.

Magnetotelluric images of the medium enthalpy Bakreswar geothermal province within a granitic gneissic complex, Eastern Indian Peninsula

AbstractThe Bakreswar geothermal province represents a medium enthalpy geothermal system with its Bakreswar and Tantloie hot springs. It lies within the Chotanagpur Granite Gneissic Complex in the eastern part of the Indian Peninsula. The province has a high heat flow and a high geothermal gradient of 90°C/km. Magnetotelluric data from 95 sites in a frequency range of 10 kHz–10 Hz were acquired over the Bakreswar geothermal province to obtain an electrical conductivity model and map the geothermal reservoir with its fluid pathways and related geological structures. Subsurface conductivity models obtained from three‐dimensional inversions of the Magnetotelluric data exhibit several prominent anomalies, which are supplemented by gravity results. The conductivity model maps three features which act as a conduit (a) a northwest–southeast trending feature, (b) an east–west trending feature to the south of the northwest–southeast trending feature (which lies 1 km north of the Oil and Natural Gas Corporation fault marked by previous studies) and (c) shallow conducting features close to Bakreswar hot spring. The northwest–southeast trending feature coincides with the boundary of the high‐density intrusive block. This northwest–southeast trending feature provides the pathway for the meteoric water to reach a maximum depth of 2.7 km, where it gets heated by interacting with deep‐seated structures and then it rises towards the surface. The radiogenic process occurring within the granites of Chotanagpur Granite Gneissic Complex provides the heat responsible for heating the meteoric water. The northwest–southeast and east–west trending features are responsible for the transport of meteoric water to deeper depths and then towards the shallow regions of the Earth. The near surface features close to the Bakreswar hot spring are responsible for carrying the water further towards the hot spring. The resistivity of these structures plotted as a function of salinity and temperatures for saline crustal fluids suggests the involvement of meteoric water. Further, applying Archie's law to this resistivity suggests that the conduit path has a porosity greater than 10%. This study successfully maps the anomalous structures which might foster the migration of geothermal fluid in Bakreswar geothermal province.

Capturing the Dynamic Processes of Porosity Clogging

AbstractUnderstanding mineral precipitation induced porosity clogging and being able to quantify its non‐linear feedback on transport properties is fundamental for predicting the long‐term evolution of energy‐related subsurface systems. Commonly applied porosity‐diffusivity relations used in numerical simulations on the continuum‐scale predict the case of clogging as a final state. However, recent experiments and pore‐scale modeling investigations suggest dissolution‐recrystallization processes causing a non‐negligible inherent diffusivity of newly formed precipitates. To verify these processes, we present a novel microfluidic reactor design that combines time‐lapse optical microscopy and confocal Raman spectroscopy, providing real‐time insights of mineral precipitation induced porosity clogging under purely diffusive transport conditions. Based on 2D optical images, the effective diffusivity was determined as a function of the evolving porous media, using pore‐scale modeling. At the clogged state, Raman isotopic tracer experiments were conducted to visualize the transport of deuterium through the evolving microporosity of the precipitates, demonstrating the non‐final state of clogging. The evolution of the porosity‐diffusivity relationship in response to precipitation reactions shows a behavior deviating from Archie's law. The application of an extended power law improved the description of the evolving porosity‐diffusivity, but still neglected post‐clogging features. Our innovative combination of microfluidic experiments and pore‐scale modeling opens new possibilities to validate and identify relevant pore‐scale processes, providing data for upscaling approaches to derive key relationships for continuum‐scale reactive transport simulations.

Pressure–Poisson equation in numerical simulation of cerebral arterial circulation and its effect on the electrical conductivity of the brain

Background and ObjectiveThis study considers dynamic modeling of the cerebral arterial circulation and reconstructing an atlas for the electrical conductivity of the brain. Electrical conductivity is a governing parameter in several electrophysiological modalities applied in neuroscience, such as electroencephalography (EEG), transcranial electrical stimulation (tES), and electrical impedance tomography (EIT). While high-resolution 7-Tesla (T) Magnetic Resonance Imaging (MRI) data allow for reconstructing the cerebral arteries with a cross-sectional diameter larger than the voxel size, electrical conductivity cannot be directly inferred from MRI data. Brain models of electrophysiology typically associate each brain tissue compartment with a constant electrical conductivity, omitting any dynamic effects of cerebral blood circulation. Incorporating those effects poses the challenge of solving a system of incompressible Navier–Stokes equations (NSEs) in a realistic multi-compartment head model. However, using a simplified circulation model is well-motivated since, on the one hand, the complete system does not always have a numerically stable solution and, on the other hand, the full set of arteries cannot be perfectly reconstructed from the MRI data, meaning that any solution will be approximative. MethodsWe postulate that circulation in the distinguishable arteries can be estimated via the pressure–Poisson equation (PPE), which is coupled with Fick's law of diffusion for microcirculation. To establish a fluid exchange model between arteries and microarteries, a boundary condition derived from the Hagen–Poisseuille model is applied. The relationship between the estimated volumetric blood concentration and the electrical conductivity of the brain tissue is approximated through Archie's law for fluid flow in porous media. ResultsThrough the formulation of the PPE and a set of boundary conditions (BCs) based on the Hagen–Poisseuille model, we obtained an equivalent formulation of the incompressible Stokes equation (SE). Thus, allowing effective blood pressure estimation in cerebral arteries segmented from open 7T MRI data. ConclusionsAs a result of this research, we developed and built a useful modeling framework that accounts for the effects of dynamic blood flow on a novel MRI-based electrical conductivity atlas. The electrical conductivity perturbation obtained in numerical experiments has an appropriate overall match with previous studies on this subject. Further research to validate these results will be necessary.

Estimating soil water content in a thorny forest ecosystem by time‐lapse electrical resistivity tomography (ERT) and HYDRUS 2D/3D simulations

AbstractDetermination of soil volumetric water content in forest ecosystems is particularly challenging due to deep rooting systems and unknown soil vertical and spatial heterogeneity. This research aims to test two undisturbed methods, electrical resistivity tomography (ERT) and HYDRUS 2D/3D, for 2D determination in a thorny forest ecosystem. The experiment consisted of infiltrating 10 L of water lasting 60 min. During infiltration, ERT measured apparent resistivity by time‐lapse measurements, and was measured with an FDR probe (EnviroSCAN) at 33, 63, 83, 97, and 163 cm depth close to the infiltration site. At the end of infiltration, a soil pit was dug, and 100 measurements of were performed with a TDR in a 10 × 10 cm regular grid. Archie law transformed soil resistivity (ERT) into using manual calibration, verified by an independent dataset. The 2D profile obtained by ERT was qualitatively compared with the HYDRUS 2D/3D one. HYDRUS 2D/3D was parametrized with calibrated parameters obtained with HYDRUS 1D using 106 days of obtained with EnviroSCAN. The results of HYDRUS 1D calibration and verification were satisfactory, with RMSE and Nash‐Sutcliffe coefficients ranging from 0.021 to 0.034 cm3 cm−3 and 0.11 to 0.77, respectively. The forward HYDRUS 2D/3D simulation disagrees with EnviroSCAN data for 33 cm depth. However, it follows the trend with near to zero variation of water content at 63 cm depth. Water content determination by ERT was satisfactory with RMSE for calibration and verification of 0.017 and 0.021 cm3 cm−3. HYDRUS 2D/3D and ERT comparisons were not equal, with a shallower wetting front by ERT and a deeper one for HYDRUS. Still, both wetting fronts agree with the wetting depth estimated by EnviroSCAN. We conclude that both methods are an alternative for determination in heterogeneous and deep soils of forest ecosystems.

Reactive transport modeling for assessing coupled hydrogeochemical processes at interfaces in deep geological repositories: from the laboratory to the real world

Abstract. Deep geological repositories with a multi-barrier concept are foreseen by various countries for the disposal of high-level radioactive waste. Simulation tools for a close-to-reality description of repository evolution scenarios are required, especially to resolve the challenging task of comparing and assessing the long-term safety of different repository concepts in different host rocks within the German site-selection process. Chemical, thermal, and pressure gradients at the interfaces of the different barriers in a repository can lead to mineral dissolution and precipitation, generating non-linear responses in transport and mechanical properties of barrier materials and host rocks. Reactive transport modeling (RTM) can be applied to investigate these perturbations and processes across temporal and spatial scales to assess subsurface evolution. Nevertheless, implementing RTM at the continuum scale while accounting for pore-scale heterogeneities and geometry evolution remains a challenge. Pore-scale simulations offer the potential to capture the complex evolution of porous media over a broad range of Peclet and Damköhler numbers, and they can be utilized to improve the RTM by using upscaling methods (Prasianakis et al., 2020). In this context, we developed “lab-on-a-chip” experiments, combining time-lapse high-resolution optical microscopy and confocal Raman spectroscopy to test extended constitutive equations to classically employed Archie's law to improve the description of changes in transport properties (e.g., diffusivity) in evolving porous media in RTM. The 3D Raman tomography of the porous media combined with pore-scale modeling enabled the derivation of upscaled transport parameters. Our results highlight the importance of calibrating pore-scale models with quantitative experiments prior to simulations over a wide range of Peclet and Damköhler numbers, whose results can be further used for the derivation of upscaled modeling parameters. The derived and parameterized constitutive equations based on simple systems have been tested in reactive transport models as a sensitivity case study to evaluate uncertainties in the predictions of the evolution of real subsurface systems such as clay–cement interfaces in deep geological repositories.

Experimental and modeling study of the diffusion path of Ce(III)-EDTA in compacted bentonite

The impact of the diffuse double-layer on the diffusion of radionuclide anions remains unclear, impeding the application of Archie's law for adsorptive anions. Through-diffusion experiments were carried out to measure the effective diffusion coefficient and distribution coefficient of Ce(III) in the presence of EDTA. A multi-porosity model, in combination with Archie's law, was used to estimate the effective diffusion coefficient. The predominant species, CeEDTA−, exhibited an effective diffusion coefficient of (0.88–1.92) × 10−11 m2/s and the distribution coefficient of (0.81–1.18) × 10−3 m3/kg at the compacted dry density of 1300–1800 kg/m3. The accessible porosity, the diffuse double-layer porosity, and the interlayer porosity were analyzed using the multi-porosity model, based on the characterization of bentonite via Scanning electron microscopy with energy dispersive spectrometry, X-ray diffractometer, and Nitrogen-Brunner-Emmett-Teller method. Due to the low external surface area of Zhisin bentonite (27.7–35.3 m2/g), the impact of the diffuse double-layer was insignificant on the total and accessible porosities. Additionally, the diffuse double-layer porosity had insignificant impact on the effective diffusion coefficient of CeEDTA− in compacted bentonite, as its value was one order magnitude lower than that of the interlayer porosity and the accessible porosity.

Induced polarization of volcanic rocks – 6: relationships with other petrophysical properties

SUMMARY The petrophysical properties of 41 volcanic samples from La Soufrière volcanoe (Guadeloupe Island, Eastern Caribbean, France) are investigated. We first measure the complex conductivity spectra of these rock samples at 4 salinities (NaCl) at laboratory conditions (∼20 °C). For each rock sample, we determine the (intrinsic) formation factor, the surface conductivity and the Cole–Cole normalized chargeability. We also measure the compressional wave velocity (dry and saturated), the shear wave velocity in saturated conditions, the (dry and saturated) thermal conductivity, the dry specific heat capacity and the permeability of the rock samples as well as their cation exchange capacity (CEC) and connected porosity. The formation factor versus porosity obeys Archie's law with a cementation exponent of 2.16 ± 0.10. The surface conductivity and the normalized chargeability are proportional to each other and to the CEC divided by the tortuosity of the material (product of the formation factor by the connected porosity) as predicted by the dynamic Stern layer model. Permeability can be predicted from the normalized chargeability and the formation factor inside one order of magnitude. The thermal conductivity and the seismic properties can be evaluated from the connected porosity of the core samples formation factors. A non-linear relationship is established between the shear wave velocity and the compressional wave velocity for the present data set and other data from the literature. Finally, we show on a specific example, how to convert an induced polarization survey on a stratovolcano into a seismic velocity model (P- and S-waves velocity distributions). We perform a specific application to Papandayan Volcano, a stratovolcano located in Java Island (Indonesia). This work paves the way to the joint inversion problem of seismic and induced polarization surveys for volcanic unrest monitoring.

Monitoring spatiotemporal soil moisture variability in the unsaturated zone of a mixed forest using electrical resistivity tomography

AbstractEuropean forests are suffering considerably from the consequences of the droughts of recent years, and the exact reasons and influencing factors for this are still not fully understood. This study was conducted to characterize the changes and dynamics of soil moisture in a mixed forest in northern Bavaria within 1 year. Since electrical resistivity correlates well with soil water content, we used two‐dimensional electrical resistivity tomography (ERT) monitoring and time‐lapse analyses to supplement punctual measurements by sensors and soil analyses to show soil moisture changes throughout a whole year (2020–2021). While the topsoil dries out significantly from summer to autumn down to a depth of about 3 m, a clear increase in soil water content and a decrease in resistivity below 3 m can be observed during winter period. Anomalies in the topsoil (0–1 m) showing lower resistivities than the surrounding substrate could be related to tree positions by additional terrestrial laser scans. A significant relationship could be found between tree crown projection area and resistivity in 1–2 m depth. We found a trend that mean resistivity below pine is lower as below beech. ERT data were also used to estimate the soil water content via Archie's law and the results correlate strongly with the measured values, but the degree of correlation varies depending on the depth level. ERT as a noninvasive method, in combination with additional data, for example, on the vitality status of individual trees, could help to better understand root water uptake and water supply to trees, especially during periods of drought.

Electrical rock typing using Gaussian mixture model to determine cementation factor

Many studies have worked on the estimation of fluid saturation as an important petrophysical property in hydrocarbon reservoirs. Based on Archie's law, proper determination of cementation factor (m) can lead to accurate values of water saturation. Given that the m is mainly affected by electrical properties of rock, electrical quality index (EQI) can be used to estimate m through a novel rock typing technique. Despite the efficient applicability of EQI for the classification of rocks, with similar electrical behaviors, into distinct electrical rock types (ERTs), manual implementation of this method is time-consuming and gets excessively more difficult for larger datasets. In this work, a fast automated version of EQI methodology was presented. As a fuzzy clustering algorithm, Gaussian mixture model (GMM) was implemented on a large quantity of carbonate and sandstone samples to cluster them into distinct ERTs based on EQI values. To this end, 100 data points were randomly selected for testing purposes, and the remaining data points were used as training subsets for carbonate and sandstone samples. An innovative hybrid EQI-GMM approach was developed to determine the optimum number of clusters. Furthermore, results of two commonly-used criteria, namely Schwarz's Bayesian Criterion (BIC) and Akaike Information Criterion (AIC), showed that they fail to specify ERTs properly. The predicted values for m by the hybrid EQI-GMM approach were more accurate (RMSE is 0.0167 and 0.0056 for carbonate and sandstone samples, respectively) than outputs of the traditional Archie’s law (RMSE is 1.6697 and 0.1850 for carbonate and sandstone samples, respectively).

Causes and Characteristics of Electrical Resistivity Variability in Shallow (<4 m) Soils in Taylor Valley, East Antarctica

AbstractAirborne electromagnetic surveys collected in December 2011 and November 2018 and three soil sampling transects were used to analyze the spatial heterogeneity of shallow (<4 m) soil properties in lower Taylor Valley (TV), East Antarctica. Soil resistivities from 2011 to 2018 ranged from ∼33 Ωm to ∼3,500 Ωm with 200 Ωm assigned as an upper boundary for brine‐saturated sediments. Elevations below ∼50 m above sea level (masl) typically exhibit the lowest resistivities with resistivity increasing at high elevations on steeper slopes. Soil water content was empirically estimated from electrical resistivities using Archie's Law and range from ∼<1% to ∼68% by volume. An increase in silt‐ and clay‐sized particles at low elevations increases soil porosity but decreases hydraulic conductivity, promoting greater residence times of soil water at low elevations near Lake Fryxell. Soil resistivity variability between 2011 and 2018 shows soils at different stages of soil freeze‐thaw cycles, which are caused predominantly by solar warming of soils as opposed to air temperature. This study furthers the understanding of the hydrogeologic structure of the shallow subsurface in TV and identifies locations of soils that are potentially prone to greater rates of thaw and resulting ecosystem homogenization of soil properties from projected increases in hydrological connectivity across the region over the coming decades.

Contribution of Resistivity Properties in Estimating Hydraulic Conductivity in Ciremai Volcanic Deposits

The hydraulic parameters of porous media, such as porosity (φ) and hydraulic conductivity (K), are the most important factors for planning and managing water exploitation from aquifers. This study aims to estimate the hydraulic conductivity parameters using the geoelectric method on volcanic deposits on the northern slope of Mount Ciremai. For this purpose, four data types were used to estimate K and φ, including lithological profiles, water table, groundwater quality, pumping test data, and vertical electrical sounding (VES). Based on Archie's law and Kozeny's equation, we get the alpha (α) values and cementation factor (m) from which the median values of α = 1.01 and m = 1.36 represent the studied aquifer. The porosity (φ) of the aquifer varies from 0.097 to 0.187 with an average of 0.141 and is spatially related to the hydraulic conductivity (kgm), which varies from 4.97 × 10-6 to 6.75 × 10-5 m/s after the application of Kozeny's equation. The hydraulic conductivity (Kp) calculated from the pumping tests varies from 9.07 × 10-6 to 1.06 × 10-4 m/s and is strongly correlated (r = 0.87). Furthermore, a relation between resistivity and hydraulic conductivity was established for the studied aquifer to estimate these parameters in sites lacking data.

Restriction of Re(VII) and Se(IV) diffusion by barite precipitation in compacted bentonite

The diffusion of anionic radionuclides in bentonite buffers for a high-level radioactive waste repository is only minimally retarded due to the anion exclusion effect and the low sorption onto the bentonite. In this study, barite precipitates in compacted barium-modified bentonite (Ba-bentonite) were used to study the restriction of the diffusion of Re(VII) and Se(IV). To this end, a synthetic porewater containing sulfate was placed in contact with compacted Ba-bentonite so that the sulfate ions could diffuse in the pores and produce barite precipitates. The Ba-bentonite and the bentonite with barium sulfate (BBS) retained the original interlayer structure based on X-ray diffractometer (XRD) analysis. Scanning electron microscopy (SEM) analysis revealed that the barite precipitates were formed in the inter-aggregate pores. A through-diffusion method was employed to measure the effective diffusion coefficient and the rock capacity factor of Re(VII) and Se(IV) in compacted Gaomiaozi (GMZ) bentonite, Ba-bentonite, and BBS. The effective diffusion coefficient decreased with increasing the compacted dry density of the three bentonites, and it decreased with increasing the amount barite precipitates in the BBS. The diffusive flux was completely stopped by the formation of high amounts of barite precipitates. The relationship between the effective diffusion coefficient and the accessible porosity could be described by Archie's law. The cementation factor of BBS was 2.9 for Re(VII) and 3.2 for Se(IV). Compared to the GMZ and Ba-bentonites, the high cementation factor of the BBS indicated a low connectedness and/or a high tortuosity. It had a better clogging effect on anion diffusion than the Ba- and GMZ bentonites.