Resistivity

LEARNING OBJECTIVES After the lesson you should be able to, i). Identify the types of geothermal reserves ii). Differentiate different types of geothermal resources iii). Describe the Hot dry rock (HDR) as a geothermal resource iv). Identify both local and global geothermal reserves COURSE CONTENT

Embung Batur Agung is a source of irrigation for residents around Embung. Depreciation of water in the reservoir occurs due to leakage from the geomembrane layer of the Embung Batur Agung. This study aims to determine the direction of leakage from the reservoir so that appropriate treatment can be carried out. This research was done using hydrogeological analysis and electrical resistivity tomography (ERT) geoelectrical measurements. ERT Geoelectrical measurement uses a dipole-dipole configuration with a spacing of 5 m and 10 m and a line length of 100 m. There are 2 lines in the southwest and southeast of the reservoir. The results of geohydrology analysis, it was found that the aquifer system around the reservoir included in the Gunungsewu aquifer system, and the dynamics of surface groundwater are controlled by faults and fractures. The results of the ERT geoelectrical measurement, there is a low anomaly which can indicate a reservoir leak at 50-60 m on line 1 which is in the southwest of the reservoir. This low anomaly has a vertical pattern as well as there is a fracture which is the cause of the reservoir leak. These low anomaly values range from 4-30 Ωm which can be interpreted as the presence of water that has conductive properties. The results of this study are expected to be used by the local government to handle the leakage of the reservoir.

Disposal of mining wastes (tailings) is one of the most severe issues related to groundwater contamination. Therefore, a properly selected disposal site helps to prevent the leakage of dissolved materials in the tailings to groundwater, especially in the karstic area. Where the karstic environment is one of the challenges facing groundwater environmental and engineering issues, for instance, groundwater exploration, vulnerability assessment, and hazard estimation. In this study, the resistivity method with a high-resolution surface data survey was carried out to investigate the pond location selection for mining tailings disposal at El Mochito mine site, northwest Honduras. The results of the two-dimensional (2-D) inversion for sixteen surveyed lines revealed that many low resistivity zones. These zones are related to water/clay-bearing zones that are structurally weak. From lines 8-12, the limestone underneath the surface is the most compact, and this is the best location in the su...

Indonesia is one of the countries with the largest geothermal potential in the world, reaching 40% of the world's potential. In geothermal areas there are several layers such as overburden, reservoirs, fractures and heat sources. Subsurface fluid flow patterns in geothermal areas are a topic that is often discussed, especially for exploration purposes. Fluid flow basically uses the principles of Darcy's law, the principle of continuity and the Navier-Stokes equation. In solving this equation, a numerical approach can be used, where the results are close to the actual value. The numerical method used in this study is the finite element method, where the geometric domain is divided into smaller domains. The shape of the two-dimensional elements used is a non-linear triangle. The purpose of this study is to describe the pattern of fluid flow in porous media, especially in the case of geothermal areas and to determine the effect of rock permeability anomalies on fluid flow patte...

Submitted for the DPP14 Meeting of The American Physical Society Improved Magnetic Reconnection Experiment at FRC Device MING XU, RUIJIE ZHOU, DANIEL VASQUEZ, TIAN-SEN HUANG, Prairie View A&M University, PRAIRIE VIEW SOLAR OBSERVATORY TEAM — With experimental facility’s improvement, magnetic reconnection has been further studied at Prairie View rotamak device. By adding one toroidal current in the central part of the rotamak device, the cutting of one magnetic field reverse configuration (FRC) as two FRCs in the experiment process becomes more obvious. Differing from the magnetic reconnection experiments conducted at other labs, where magnetic reconnection is formed with two ware-coiled currents buried in a chamber with large scale magnetic field, in our magnetic reconnection experiment the main source of the magnetic field is plasma current. Thus, the magnetic reconnection experiments conducted at rotamak device are closer to the one occurring in the space and on the sun. At the pr...

Millimeter waves are increasingly used in modern telecommunication systems for wireless data transmission. However, higher path loss, especially caused by non-line-of-sight scenarios, remains challenging. The design of an electrically controllable reflector for the millimeter-wave range is elaborated and presented in this manuscript. The reflector design was based on distributed ferroelectric ceramic elements and could be used in a frequency range up to 100 GHz. The issue of the ferroelectric reflector impedance matching was analyzed in detail. Two possible implementations of the reflector for indoor and outdoor communication systems were considered and simulated. The prototype of the proposed reflector for an operating frequency of 60 GHz was manufactured. Both simulation and measurement results demonstrated the beam steering by the proposed ferroelectric reflector.

Three-dimensional electrical resistivity and induced polarization data were collected on an unstable Alpine rock glacier in Val Thorens (Vanoise massif, France). In addition to these field data, we also performed induced polarization measurements during freeze and thaw using a soil sample and the poorly mineralized water, both from this site. In the tomograms, the electrical conductivity and the normalized chargeability show very distinctly the presence of the rock ice mixture. The chargeability itself is however quite constant over the entire investigated area with the exception of a small area associated with the presence of carboniferous rocks rich in graphite. The background chargeability is close to the dimensionless number R = 8 × 10 À2 , which is consistent with the prediction of the dynamic Stern layer model for the polarization of porous media. The theory implies that this dimensionless number R is independent on saturation and temperature in agreement with field observations. A main implication of this observation is that the classical Archie's law cannot be applied to describe the electrical conductivity in this type of environments with poorly mineralized pore water. Surface conductivity dominates the measured conductivity of the materials implying in turn that the electrical conductivity is related to both the water content and cation exchange capacity of the material. We propose new equations for both the electric conductivity and the normalized chargeability in this type of environments. Plain Language Summary Induced polarization is a geophysical method looking at imaging the 3D distribution of properties related to the ability of rocks to store reversibly electrical charges under the application of a primary electrical field. This method has never been applied to rock glaciers. A field application and a laboratory experiment demonstrate the usefulness of this method to characterize Alpine rock glaciers and point up some shortcomings in the interpretation of electrical conductivity tomography done by previous authors in this type of environments.

We consider a mixture made of dispersed metallic particles immersed into a background material saturated by an electrolyte. Below the freezing temperature (typically 0°C to −4°C), a fraction of the liquid water in the pore space is transformed into ice, whereas the salt remains segregated into the liquid-pore water solution. Our goal is to understand how freezing affects the complex conductivity (induced polarization) of such mixtures. Complex conductivity measurements (96 spectra) are performed in a temperature-controlled bath equipped with a high-precision impedance meter. We cover the temperature range from þ20°C to −15°C to −18°C and the frequency range from 10 −2 Hz to 45 kHz. The spectra are fitted with a double Cole-Cole complex conductivity model. A finite-element model is used to further analyze the mechanisms of polarization by considering an intragrain polarization mechanism for the metallic particles and a change of the conductivity of the background material modeled with an exponential freezing curve. This curve is used to relate the liquid water content to the temperature. In the context of freezing, we test all the aspects of the intragrain polarization model developed in the previous papers of this series, at least for a weakly polarizable background material. The Cole-Cole exponent and the chargeability are observed to be essentially independent of temperature including in freezing conditions. This means that all the relaxation times of the system follow the same temperature dependence and that the chargeability is controlled by the volume fraction of metal. The instantaneous conductivity (high-frequency conductivity) and the relaxation times depend on the temperature in a predictable way, and their product can be considered to be essentially temperature independent. The analytical and numerical models can reproduce the inverse relationship between the relaxation time and the instantaneous conductivity.

We use a basket geothermal heat exchanger during 518 hr to freeze a portion of soil. This field experiment is monitored using time lapse electrical conductivity tomography and a set of 47 in situ temperature sensors. A frozen soil core characterized by negative temperatures and low conductivity values (<10 −3 S/m) develops over time. A petrophysical model describing the temperature dependence of the electrical conductivity in freezing conditions is applied to the field data and compared to two laboratory experiments performed with two core samples from the test site. The results show that this petrophysical model can be used to interpret field measurements bridging electrical conductivity to temperature and liquid water content.

Spectral induced polarization spectra were carried out on three graphitic schists and two graphitic sandstones. The microstructural arrangement of graphite of two graphitic schists was studied with thin sections using transmitted and reflected light optical and electron microscopic methods. Chemical maps of selected areas confirm the presence of carbon. The complex conductivity spectra were measured in the frequency range 10 mHz to 45 kHz and in the temperature range +20°C down to −15°C. The measured spectra are fitted with a double Cole-Cole complex conductivity model with one component associated with the polarization of graphite and the second component associated with the Maxwell-Wagner polarization. The Cole-Cole exponent and the chargeability are observed to be almost independent of temperature including in freezing conditions. The conductivity and relaxation time are dependent on the temperature in a predictable way. As long as the temperature decreases, the electrical conductivity decreases and the relaxation time increases. A finite element model is able to reproduce the observed results. In this model, we consider an intragrain polarization mechanism for the graphite and a change of the conductivity of the background material modeled with an exponential freezing curve. One of the core sample (a black schist), very rich in graphite, appears to be characterized by a very high conductivity (approximately 30 S/m). Two induced polarization profiles are discussed in the area of Thorens. The model is applied to the chargeability data to map the volumetric content of graphite.

We investigate the thermal dependence of the complex conductivity of nine porous materials in the temperature range +20°C to −10 or −15°C. The selected samples include three soils, two granites, three clay-sands mixes, and one graphitic tight sandstone. A total of 12 experiments is conducted with one sample tested at three different salinities. Our goal is to use this database to extend the dynamic Stern layer polarization model in freezing conditions. We observe two polarization mechanisms, one associated with the effect of the change in the liquid water content and its salinity upon the polarization of the porous material. A second mechanism, at higher frequencies (>10 Hz), is likely associated with the polarization of ice. At low frequencies and above the freezing point, the in-phase and quadrature conductivities depend on temperature in a predictable way. This dependence is due to the dependence of the mobility of the charge carriers with temperature. Below the freezing point, the in-phase and quadrature conductivity follow a brutal decay with temperature. This dependence is modeled through an exponential freezing curve function. We were also able to determine how the (apparent) formation factor and surface conductivity change with temperature and water content below the freezing point. Our model is able to replicate the data at low frequencies and predicts correctly the fact that the ratio between the normalized chargeability and the surface conductivity is independent of the water content and temperature and equals a well-defined dimensionless number R.

In the construction sector, it is necessary to have information on subsurface conditions to get treatment appropriate to the construction on it. This study aims to get an overview of the subsurface conditions to support the construction of the case study site. Direct methods can obtain subsurface conditions through soil investigation of boring (SPT) and sondir (CPT), as well as indirect methods by approaching physical parameters in the form of geophysics and georadar. In this study, the subsurface conditions were studied using geoelectric (indirect method) and sondir (direct method), and the correlation between the two was analyzed. Geoelectrical testing used MAE X612-EM+ equipment with 48 electrodes, a configuration of 2 meters between electrodes, and a total length of 94 meters. The study shows that the subsurface conditions at the study site are dominated by soft material with a resistivity value of 36.2 - 55.7 Ωm, which correlates with clay. At a distance of 34 meters to 58 meters with a depth of about 3.0 meters, an area with a resistivity value of <10 Ωm is obtained which indicates the presence of water potential. Sondir testing used bi-conus with a manual machine with a capacity of 2.5 tons. The results of sondir investigation at a depth of 0.0 - 3.8 meters obtained a conus resistance value (qc) of 20 - 55 kg/cm2 correlated with a resistivity value of 36.2 - 55.7 Ωm with a relative density of soil from weak to medium. Meanwhile, at a depth of 3.8 – 4.6 meters, the qc value of 60 - 210 kg/cm2 is correlated with a resistivity value of > 55.7 Ωm with a relative soil density from medium to large. At a distance of 48 meters and a depth of >10 meters, solid and hard material indications were found with a resistivity value of >202 Ωm.

The concrete electrical resistivity is a prominent parameter in structural health monitoring, since, along with corrosion potential, it provides relevant qualitative diagnosis of the reinforcement corrosion. This study proposes a simple expression to reliable determine resistivity from the concrete electrical resistance (RE) provided by the corrosion sensor of the Integrated Network of Sensors for Smart Corrosion Monitoring (INESSCOM) we have developed. The novelty here is that distinct from common resistivity sensors, the cell constants obtained by the proposed expression are intended to be valid for any sensor implementation scenario. This was ensured by studying most significant geometrical features of the sensor in a wide set of calibration solutions. This embedded-sensor approach is intended to be applicable for RE measurements obtained both using potential step voltammetry (PSV, used in the INESSCOM sensor for corrosion rate measurement) and alternating current methods. In thi...

The main objective of this study was to analyze the influence that the addition of finely ground hydrated lime has on chloride-induced reinforcement corrosion in eco-efficient concrete made with 50% cement replacement by fly ash. Six tests were carried out: mercury intrusion porosimetry, chloride migration, accelerated chloride penetration, electrical resistivity, and corrosion rate. The results show that the addition of 10–20% of lime to fly ash concrete did not affect its resistance to chloride penetration. However, the cementitious matrix density is increased by the pozzolanic reaction between the fly ash and added lime. As a result, the porosity and the electrical resistivity improved (of the order of 10% and 40%, respectively), giving rise to a lower corrosion rate (iCORR) of the rebars and, therefore, an increase in durability. In fact, after subjecting specimens to wetting–drying cycles in a 0.5 M sodium chloride solution for 630 days, corrosion is considered negligible in fl...