Project

German Geophysical Society (DGG) Working Group IP (AK IP)

Goal: - exchange of information on research and experience with IP and SIP
- development of standards and reference materials
- collecting ideas for further work and projects
- disseminate the knowledge on IP

This project site is supposed to increase the visibility of IP / SIP related research and according publications. The working group is open to everyone for active or passive membership.

Methods: Induced Polarization, Spectral Induced Polarization

Date: 1 March 2005

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Jana H. Börner
added 5 research items
Carbonate formations still present a challenging target with regard to reservoir characterization as they possess a wide range of pore types and sizes as well as interconnected and isolated pore space. In this study a set of micritic and oomoldic carbonate samples was investigated with three measurement techniques (magnetic resonance (NMR), mercury intrusion (MICP), and spectral induced polarization (SIP, in a frequency range from 5mHz to 100 Hz)) which provide information about a rock's pore space indirectly based on different physical principles. The aims of the study were to combine these pieces of information to characterize the pore space of mud-dominated and grain-dominated carbonate rocks and to investigate potential correlations between pore space properties and SIP-derived parameters. Pore body and pore throat size distributions were derived from NMR and MICP data, respectively, and interpreted in terms of dominant pore throat (rt) radius, pore body (rb) radius and the rb/rt ratio. For validation of the NMR-derivedrb distributions, scanning electron microscope images were used for the computation of image-derived pore size distributions. The SIP data were interpreted in terms of characteristic features for oomoldic and micritic samples. Phase shift, real (σ′) and imaginary part (σ′′) of complex conductivity, respectively, were fitted with Cole-Cole models and the characteristic parameters relaxation time τ, chargeability m, and frequency dependence c were derived for each sample. Subsequently, these parameters were interpreted with regard to correlations with rb,rt, and rb/rt and specific surface Spor. The results indicate that grain-dominated carbonates possess comparatively large radii rb and rt and low Spor, which seems to go along with sharp phase peaks (i.e. high c values) and a low absolute phase level (and therefore low chargeability m). The mud-dominated carbonates, in contrast, possess relatively small radii rb and rt and high Spor which is obviously associated with broad phase peaks (i.e. low c values) and a comparatively high phase level resulting in high m values. τ, in contrast, was found to decrease with increasing ratio rb/rt and may therefore have similar values in both micritic and oomoldic samples. Consequently, the results of this study contribute to a better understanding of the petrophysical properties of carbonate rocks as a function of their pore space characteristics.
We analyzed in the laboratory the frequency-dependent, complex-valued, electrical conductivity of a graphitic black schist and an augen gneiss, both collected in the Main Central Thrust shear zone in the Himalayas of central Nepal, which was heavily affected by the deadly Mw7.8 Gorkha earthquake in 2015. We focused on anisotropy and salinity dependence of both cores and crushed material as well as the impact of CO2 on conductivity. This black schist possesses an extraordinarily high polarizability and a highly frequency-dependent conductivity. Its anisotropy is very pronounced. The investigations can relate the main polarization feature to disseminated, aligned plates of graphite. By contrast, the augen gneiss shows low polarizability and a moderately anisotropic conductivity dominated by the pore-filling brine. We further demonstrate that neglecting the complex and frequency-dependent nature of conductivity can lead to serious misinterpretation of magnetotelluric data during inversion if highly polarizable rocks are present.
The spectral complex conductivity of a water-bearing sand during interaction with carbon dioxide (CO2) is influenced by multiple, simultaneous processes. These processes include partial saturation due to the replacement of conductive pore water with CO2 and chemical interaction of the reactive CO2 with the bulk fluid and the grain-water interface. We present a laboratory study on the spectral induced polarization of water-bearing sands during exposure to and flow-through by CO2. Conductivity spectra were measured successfully at pressures up to 30 MPa and 80 °C during active flow and at steady-state conditions concentrating on the frequency range between 0.0014 and 100 Hz. The frequency range between 0.1 and 100 Hz turned out to be most indicative for potential monitoring applications. The presented data show that the impact of CO2 on the electrolytic conductivity may be covered by a model for pore-water conductivity, which depends on salinity, pressure and temperature and has been derived from earlier investigations of the pore-water phase. The new data covering the three-phase system CO2-brine-sand further show that chemical interaction causes a reduction of surface conductivity by almost 20 per cent, which could be related to the low pH-value in the acidic environment due to CO2 dissolution and the dissociation of carbonic acid. The quantification of the total CO2 effect may be used as a correction during monitoring of a sequestration in terms of saturation. We show that this leads to a correct reconstruction of fluid saturation from electrical measurements. In addition, an indicator for changes of the inner surface area, which is related to mineral dissolution or precipitation processes, can be computed from the imaginary part of conductivity. The low frequency range between 0.0014 and 0.1 Hz shows additional characteristics, which deviate from the behaviour at higher frequencies. A Debye decomposition approach is applied to isolate the feature dominating the data at low frequencies. We conclude from our study that electrical conductivity is not only a highly sensitive indicator for CO2 saturation in pore space. When it is measured in its full spectral and complex form it contains additional information on the chemical state of the system, which holds the potential of getting access to both saturation and interface properties with one monitoring method.
Thomas Günther
added 3 research items
Data and scripts for the scientific journal article: Martin, T., Günther, T., Flores Orozco, A. & Dahlin, T. (2020): Evaluation of spectral induced polarization field measurements in time and frequency domain, J. Appl. Geophys., 180, 104141, doi:10.1016/j.jappgeo.2020.104141. The paper deals with the comparison of instruments for measuring induced polarization (IP) data, both in frequency domain (FD) as well in time-domain. Four instruments have been used to measure two profiles (IP1: a=1m, IP5: a=5m) over a known blackshale near the town Schleiz in Thuringia, Germany. Preface: Our vision is not only to publish scientific results, but also openly demonstrate how the results have been produced. This includes the raw data, processed data and inversion results, but also all scripts that have been used for it in a reproducible way. The scripts use the pyBERT (Python Boundless Electrical Resistivity Tomography) based on the pyGIMLi (Python Geophysical Inversion and Modelling Library) computational framework. Here, we used the pyBERT version 2.3.1 based on pygimli 1.1.1, but it should be reachable by similar versions as well. All is based on the classes FDIPdata and TDIPdata. For installing, we refer to the webpages www.pygimli.org and gitlab.com/resistivity-net/bert
Historical slag dumps are of increasing interest due to economic, environmental or archaeological reasons. Geophysical investigations can help accessing the potential reuse of slag material to recover metallic raw material or the estimation of the hazard potential of the buried slag material due to dissolution occurrence. In our study, we have investigated various slag material in the laboratory with the spectral induced polarization (SIP) method, obtained from different historical slag dumps, located in the Harz Mountains, Germany. We also present SIP results from field measurements at a historical slag dump where most of the slag samples reveal high amounts of iron, zinc, silica, and barium. Our results reveal a discrimination between three different slag grades (low, medium, high) by using the imaginary conductivity σ” at a medium frequency (1–10 Hz) in both laboratory and field. Furthermore, additional information is obtained by a classification based on the spectral polarization behaviour and considering the field frequency range (0.1 Hz – 100 Hz). Five different types of spectra (ascending, descending, constant, maximum and minimum type) can be discriminated and recognized in the laboratory and in distinct areas of the slag dump. Even though a direct comparison between the laboratory and field results still needs to be proven, the buried slag material can be differentiated from the surrounding material by the polarization magnitude.
Matthias Bücker
added a research item
Die Methode der Spektralen Induzierten Polarisation (SIP) basiert auf der Vermessung der komplexen Leitfähigkeit heterogener Medien. Polarisationseffekte an den mikroskopischen Grenzflächen zwischen festen und flüssigen Bestandteilen geologischer Materialien führen zu charakteristischen frequenzabhängigen Variationen der komplexen Leitfähigkeit. Im Frequenzbereich bis etwa 1 kHz werden dafür vor allem Polarisationseffekte in der elektrischen Doppelschicht verantwortlich gemacht, die im Elektrolyt gelegen die meist negativ geladenen Mineraloberflächen bedeckt. Mechanistische Modelle dieser Polarisationseffekte können bereits viele experimentelle Beobachtungen erklären. Dazu gehören etwa die Variation der Relaxationszeit der Polarisation mit dem Quadrat der dominierenden geometrischen Längenskala oder die Abhängigkeit der Polarisationsstärke mit der Ladungsstärke in der Doppelschicht. Lange Zeit standen für die Erklärung solcher experimentellen Daten lediglich analytische Modelle für sehr einfache Modellgeometrien wie z.B. Kugeln oder Ellipsoide zur Verfügung. Nach der Einführung eines relativ einfach handhabbaren numerischen Finite-Elemente-Modells für die Polarisationsprozesse in der Doppelschicht, können nun aber auch komplexere Geometrien modelliert werden. Hier präsentieren wir Ergebnisse von Simulationen, mit denen wir den Einfluss (1) der Oberflächenrauigkeit kugelförmiger Mineralkörner, (2) toter Poren, sowie (3) der Wechselwirkung zwischen benachbarten Körnern untersucht haben. So macht sich die Oberflächenrauigkeit durch das Auftreten eines zusätzlichen Peaks im Imaginärteil bzw. der Phase der Leitfähigkeit bemerkbar. In toten Poren, d.h. in elektrolytgefüllte Poren, die von allen Seiten von einer nichtleitenden Matrix umschlossen sind, beobachten wir eine Polarisation der elektrischen Doppelschicht, die die gleiche Relaxationszeit aufweist wie ein gleichgroßes Mineralkorn. Die Wechselwirkung zwischen benachbarten Körnern führt schon bei großen Abständen (relativ zur Ausdehnung der Doppelschicht) zu einer merklichen Abnahme der Stärke des Polarisationseffekts. Unsere Studien illustrieren damit die Nützlichkeit des verwendeten numerischen Modells und das damit verbundene Potential zur Verbesserung unseres grundlegenden Verständnisses der Polarisationsprozesse auf der Mikroskala.
Norbert Klitzsch
added 6 research items
Spectral induced polarisation (SIP) can be applied to derive hydraulic permeabilities by using the complete spectral information, i.e., by analyzing the frequency dependence (typically in the range from 1 mHz to 10 kHz) in terms of relaxation times. The relation between the Cole Cole relaxation time and the hydraulic conductivity was deduced from laboratory measurements on sedimentary rocks. Unfortunately, this relation can not be directly used to derive hydraulic conductivities from field data because they are influenced by electromagnetic coupling. This is crucial even for small arrays and particularly for conductive environments and at high frequencies. Coupling occurs between the electric wires and the ground as well as among the wires themselves. We focus on inductive coupling of the current wires to the ground. The influence of inductive coupling will be shown. Furthermore, a method for the removal of the inductive coupling is introduced and applied for a field example.
In this study, spectral induced polarization (SIP) spectra were generated numerically to better understand how actual rock microstructure and electrolyte properties in rock pores affect the spectral pattern, i.e., the characteristic relaxation time of polarization as well as the polarization strength of a rock pore system. The dynamics of charge carriers in three-dimensional pore systems were simulated using a frequency-dependent formulation of the Nernst-Planck-Poisson (NPP) ion-transport equations. Basically, a pore-system model of alternating stacked cylinders of two different sizes was studied considering the electrical double layer (EDL). A reduced cationic mobility-resulting from increased adsorption of these cations at the rock-water interface-was assumed within the EDL. By solving the NPP equations using the finite element method, complex resistivity phase spectra were generated. Subsequently, the effect of pore structural properties and electrolyte conductivity on the magnitude and frequency position of the characteristic resistivity phase minimum of rocks was studied. The following results were found: First, regarding pore geometry, the characteristic frequency of the phase minimum f(min) decreases with increasing pore length of the large pore. Second, both small pores having a radius of a few Debye lengths combined with larger pores are needed to ensure detectable phase amplitudes. Third, with regard to electrolyte concentration, the phase amplitude is inversely proportional to the concentration, whereas f(min) remains constant. Because the studied model does not provide a direct and exclusive link between the simulated electrical properties and pore throat size, further research is needed here to specify a convincing SIP interpretation method for improved permeability estimation.
Recently, significant progress has been made in understanding low frequency complex conductivity measurements of rocks. The relevant publications study these methods in two different ways: On the one hand, petrophysical interpretation has been improved in terms of theoretical approaches. These approaches are either modifications of pore size related membrane polarization concepts or rely on grain size related polarization models in combination with semi-empirical model function parameterizations. On the other hand, extensive petrophysical studies provide insight in dependencies of IS parameters on structural and electrochemical rock properties. We aim at assessing the results of published theoretical and experimental findings for a reference system, consisting of sintered porous glass samples. Thereby, we benefit from well characterized samples, which allow for direct tests of theoretical predictions and empirical relations. We find that: (1) The correlation σ″~Sm is stronger than σ″~Spor for a wide range of fluid conductivities and frequencies above 1Hz. (2) Correlation coefficients for the imaginary conductivity to inner surface area relations are strongly frequency dependent. (3) Normalized chargeability, obtained by fitting a Cole-Cole model to the spectral data, provides a fair alternative to single frequency information. (4) Correlation breaks down for disturbed fluid-surface interaction by wettability manipulation. (5) Salinity dependence of proportionality factors a1=Sm/σ″ and a2=Spor/σ″ due to a salinity dependent partition coefficient is confirmed qualitatively. Quantitative theoretic predictions of a1 or a2 fail due to the assumption of non-reduced Stern layer mobility for clay free silica. (6) Earliest grain size related models provide the best quantitative estimate of relaxation time. (7) Results agree well with published data for sands and sandstones with respect to (i) quantitative estimates of a1 or a2 and (ii) influences of rock structural parameters on relaxation time.
Tina Martin
added a research item
Spectral information obtained from induced polarization (IP) measurements can be used in a variety of applications and is often gathered in frequency domain (FD) at the laboratory scale. In contrast, field IP measurements are mostly done in time domain (TD). Theoretically, the spectral content from both domains should be similar. In practice, they are often different, mainly due to instrumental restrictions as well as the limited time and frequency range of measurements. Therefore, a possibility of transition between both domains, in particular for the comparison of laboratory FD IP data and field TD IP results, would be very favourable. To compare both domains, we conducted laboratory IP experiments in both TD and FD. We started with three numerical models and measurements at a test circuit, followed by several investigation at different wood and sandstone samples. Our results demonstrate that the differential polarizability (DP), which is calculated from the TD decay curves, can be compared very well with the phase of the complex electrical resistivity. Thus, DP can be used for a first visual comparison of FD and TD data, which also enables a fast discrimination between different samples. Furthermore, to compare both domains qualitatively, we calculated the relaxation time distribution (RTD) for all data. The results are mostly in agreement between both domains, however, depending on the TD data quality. It is striking that the DP and RTD results are in better agreement for higher data quality in TD. Nevertheless, we demonstrate that IP laboratory measurements can be carried out in both TD and FD with almost equivalent results. The RTD enables a good comparability of FD IP laboratory data with TD IP field data.
Matthias Bücker
added 2 research items
Biogeochemical hot spots are defined as areas where biogeochemical processes occur with anomalously high reaction rates relative to their surroundings. Due to their importance in carbon and nutrient cycling, characterization of hot spots is critical to accurately predict carbon budgets in the context of climate change. However, biogeochemical hot spots are difficult to identify in the environment, as sampling resolutions are often too coarse to find these areas in the subsurface. Here, we present imaging results of a geophysical survey using the non-invasive induced polarization (IP) method to identify biogeochemical hot spots of carbon turnover in a minerotrophic wetland. To interpret the field-scale IP signatures, geochemical analyses were performed on freeze-core samples obtained in areas characterized by anomalously high and low IP responses. Our results reveal large variations in the electrical response, with the highest IP phase values (> 20 mrad) corresponding with high concentrations of phosphates (> 4000 μM), an indicator of carbon turnover. Moreover, analysis of the freeze core reveal negligible concentrations of iron sulfides. The extensive geochemical and geophysical data presented in our study demonstrates that IP images can assess changes in the biogeochemical activity in peat, and identify hot spots.
Karst water resources play an important role in drinking water supply but are highly vulnerable to even slight changes in climate. Thus, solid and spatially dense geological information is needed to model the response of karst hydrological systems to such changes. Additionally, environmental information archived in lake sediments can be used to understand past climate effects on karst water systems. In the present study, we carry out a multi-methodological geophysical survey to investigate the geological situation and sedimentary infill of two karst lakes (Metzabok and Tzibaná) of the Lacandon Forest in Chiapas, southern Mexico. Both lakes present large seasonal lake-level fluctuations and experienced an unusually sudden and strong lake-level decline in the first half of 2019, leaving Lake Metzabok (maximum depth ∼25 m) completely dry and Lake Tzibaná (depth ∼70 m) with a water level decreased by approx. 15 m. Before this event, during a lake-level high stand in March 2018, we collected water-borne seismic data with a sub-bottom profiler (SBP) and transient electromagnetic (TEM) data with a newly developed floating single-loop configuration. In October 2019, after the sudden drainage event, we took advantage of this unique situation and carried out complementary measurements directly on the exposed lake floor of Lakes Metzabok and Tzibaná. During this second campaign, we collected time-domain induced polarization (TDIP) and seismic refraction tomography (SRT) data. By integrating the multi-methodological data set, we (1) identify 5–6 m thick, likely undisturbed sediment sequences on the bottom of both lakes, which are suitable for future paleoenvironmental drilling campaigns, (2) develop a comprehensive geological model implying a strong interconnectivity between surface water and karst aquifer, and (3) evaluate the potential of the applied geophysical approach for the reconnaissance of the geological situation of karst lakes. This methodological evaluation reveals that under the given circumstances, (i) SBP and TDIP phase images consistently resolve the thickness of the fine-grained lacustrine sediments covering the lake floor, (ii) TEM and TDIP resistivity images consistently detect the upper limit of the limestone bedrock and the geometry of fluvial deposits of a river delta, and (iii) TDIP and SRT images suggest the existence of a layer that separates the lacustrine sediments from the limestone bedrock and consists of collapse debris mixed with lacustrine sediments. Our results show that the combination of seismic methods, which are most widely used for lake-bottom reconnaissance, with resistivity-based methods such as TEM and TDIP can significantly improve the interpretation by resolving geological units or bedrock heterogeneities, which are not visible from seismic data. Only the use of complementary methods provides sufficient information to develop comprehensive geological models of such complex karst environments
Andreas Weller
added 56 research items
Die geoelektrischen Erkundungsmethoden nutzen die Unterschiede in den elektrischen Eigenschaften von Gesteinen oder Materialien im Untergrund aus. Prinzipiell kann man davon ausgehen, dass dort, wo sich die Erkundungsobjekte (Erzkörper, archäologische Strukturen) nicht in ihren elektrischen Eigenschaften vom umgebenden Gestein signifikant unterscheiden, auch keine erfolgreiche Erkundung durchgeführt werden kann. Im Umkehrschluss gilt, dass bei besonders markanten Kontrasten in den elektrischen Eigenschaften auch die Chancen für einen geoelektrischen Nachweis am größten sind. Um die Erfolgsaussicht schon im Vorfeld abschätzen zu können, gewinnt die Untersuchung der elektrischen Eigenschaften von Gesteinen und Materialien mit Laborversuchen an Bedeutung. Dieser Aufgabenstellung widmet sich u.a. die Petrophysik, die das Bindeglied zwischen den Materialwissenschaften und der Erkundungsgeophysik darstellt. Für geoelektrische Untersuchungen sind eine Vielzahl von Methoden entwickelt worden, die sich hinsichtlich der Anregung elektrischer oder elektromagnetischer Felder und dem nutzbaren Frequenzbereich unterscheiden. Als Quellen werden sowohl natürliche Felder (Eigenpotenzial oder elektromagnetische Variationen) als auch spezielle Geber genutzt, die galvanisch oder kapazitiv gekoppelt Strom in den Untergrund einspeisen oder als Spulen bzw. Antennen elektromagnetische Felder aussenden. Der Frequenzbereich reicht dabei von Gleichstromfeldern bei der klassischen Widerstandsgeoelektrik bis hin zu elektromagnetischen Feldern im Mega- bis Gigahertzbereich beim Georadar. Dieser breite Frequenzbereich bei den unterschiedlichen Feldmessmethoden erfordert, die Frequenzabhängigkeit der elektrischen Eigenschaften der Gesteine und Materialien zu untersuchen. Dabei werden im niederfrequenten Bereich die elektrische Leitfähigkeit und bei höheren Frequenzen bevorzugt die Dielektrizitätszahl betrachtet. Beide Größen sind
Das Verfahren zur Bestimmung des spezifischen elektrischen Gesteinswiderstandes wird in der Bohrlochmessung bei der Untersuchung der in einer Bohrung anstehenden Schichten angewendet. Es wird das Ziel verfolgt, die Qualität der Meßergebnisse bei der Widerstandsmessung zu verbessern und bei erheblicher Senkung des technischen Aufwandes die Aussagesicherheit zu steigern. Es besteht die Aufgabe, die bohrlochbedingten Einflüsse auf die Meßwerte der Widerstandsmessung weitgehend herabzusetzen und eine quasi-Stromfokussierung anstelle einer schaltungstechnischen Stromfokussierung vorzunehmen. Erfindungsgemäß wird die Aufgabe dadurch gelöst, daß mit Hilfe einer prinzipiell anderen Elektrodenanordnung mehrere Potentialwerte gemessen werden und durch ihre rechnerische Verknüpfung der Widerstandswert als quasifokussierte Anordnung ermittelt werden kann. Die Elektrodenanordnung in der Bohrlochmeßsonde besteht aus der Stromelektrode, der nach einer Seite vier Meßelektroden in vorbestimmten Abständen zugeordnet sind, wobei diese Abstände sich nach dem notwendigen Auflösungsvermögen richten, daß durch die zu erwartenden Schichtmächtigkeiten bestimmt wird.
Matthias Bücker
added 42 research items
Geophysical methods are widely used for landslide investigation to delineate depth and geometry of the sliding plane. In particular, electrical resistivity tomography (ERT) is often used because both porosity and water saturation control the electrical resistivity of the subsurface materials and are critical for slope stability. Moreover, ERT can be employed to monitor changes in pore-fluid pressure which is an important factor triggering landslides. However, the interpretation of ERT results in clay-rich landslides can be challenging considering that high electrical conductivity values may not only be related to an increase in saturation but also to the surface conduction mechanism, which becomes dominant in the presence of clays. Recently, environmental investigations have demonstrated an improved subsurface characterization through induced polarization (IP) imaging, an extension of the ERT method, which permits to gain information about electrical conductive and capacitive (i.e., polarization effect) properties of the subsurface. As the polarization effect is mainly controlled by surface charge, which is large in clays, IP images are expected to improve the lithological interpretation and overcome the limitations of the ERT method. Additionally, measurements collected over a broad frequency bandwidth, the so-called spectral IP (SIP), have been successfully used in laboratory experiments to quantify textural and hydrogeological parameters. However, the application of SIP field measurements for the delineation of hydrogeological structures in landslides has not been addressed to date. To fill this gap, in this study we present SIP imaging results for data collected at the La Valette landslide (South East French Alps), where an existing geotechnical model of the landslide is available for evaluation. Moreover, our study provides a detailed revision on the collection and processing of SIP datasets, as well as a description of the diverse sources of error in IP surveys, to stress the importance of data-error quantification for a quantitative application of the SIP method. Our results demonstrate that adequate data processing allows obtaining consistent results at different frequencies and independently of the measuring protocol. Furthermore, the frequency dependence of the complex conductivity obtained in the field-scale SIP survey is consistent with earlier laboratory experiments. In conclusion, our study shows the potential of the SIP method to improve our understanding of subsurface properties, and an improved delineation of the contact between the mobilized material and the bedrock as well as variations in the clay content within the landslide and the bedrock.
This thesis is concerned with mechanistic pore-scale models, which relate the induced-polarization (IP) response of geologic materials to the underlying physical and chemical processes. Although a sound understanding of these processes is essential for the interpretation of measured IP responses, the development of suitable mechanistic models is lagging far behind the fast growing amount of experimental IP data. Therefore, the main objective of this thesis is to improve theoretical models and advance the general understanding of the polarization processes. The first development is an analytic model to predict the influence of an immiscible liquid hydrocarbon phase on the membrane-polarization mechanism occurring in electrolyte-filled pore constrictions. The hydrocarbon is modelled as an electrically insulating phase with a negatively charged surface. Magnitude and phase of the predicted electrical conductivity of hydrocarbon-contaminated materials decrease with increasing hydrocarbon saturation irrespective of whether the hydrocarbon phase is wetting or non-wetting. Only non-wetting hydrocarbon droplets with highly charged surfaces yield an increase of the magnitude with the hydrocarbon saturation and a slight increase of the phase at intermediate hydrocarbon concentrations. This prediction offers the first theoretical explanation for a similar experimentally determined relation between complex conductivity and hydrocarbon saturation. The next two parts of this thesis examine the electrode-polarization mechanism responsible for the IP response of metal-bearing materials. The polarization of uncharged metallic particles is studied based on an electrochemical model, which includes the effect of oxidation-reduction reactions at the particle surface. The full solution of the underlying Poisson-Nernst-Planck (PNP) system is presented, which allows to visualize the micro-scale manifestations of two simultaneously acting polarization mechanisms. The first mechanism is related to the dynamic charging of field-induced diffuse layers and the second is a volume-diffusion mechanism activated by reaction currents through the particle surface. For the relaxation times of both processes analytic expressions are derived and a critical particle radius is determined. While the response of particles smaller than this radius is mainly determined by the diffuse-layer polarization, the effect of the volume-diffusion mechanism becomes significant around larger particles. The model is then extended to investigate the effect of surface charge on electrode polarization. Besides the dynamic charging of field-induced diffuse layers and the volume-diffusion processes related to the reaction currents, the numeric solution of the modified PNP system reveals the action of an additional volume-diffusion process caused by the unequal transport rates of anions and cations within the static diffuse covering the charged surface. This mechanism is found to have a second-order effect on the macroscopic polarization response, which is still dominated by the first two mechanisms. While the volume-diffusion process due to the reaction currents remains practically unaffected by the surface charge, a moderate increase of the low-frequency conductivity and the relaxation time as well as a slight reduction of the polarization magnitude with the surface charge are observed if the diffuse-layer relaxation dominates, i.e. in the case of small particles. In the last part of this thesis, the coupled polarization of Stern and diffuse layers covering dielectric surfaces is treated in a generalized numeric framework. First, this framework is used to model the response of spherical particles and guide the development of an improved analytic model for the coupled polarization of Stern and diffuse layer. Subsequently, it is applied to a cylindrical pore-constriction geometry. In the limiting case of a pure diffuse-layer polarization, the corresponding numeric results can be matched by an improved analytic membrane-polarization model. In both geometries, the response of the Stern layer dominates as long as the charged surfaces are not interconnected at the system scale. With increasing degree of interconnectivity, however, the response of the diffuse layer becomes more important and in the case of fully interconnected surfaces becomes as strong as the response of the Stern layer. In summary, this thesis brings together significant improvements of analytic models for all relevant induced-polarization mechanisms: Membrane polarization, electrode polarization, and Stern- and diffuse-layer polarization. The carefully validated numeric modelling framework furthermore lays the foundation for the future investigation of more realistic geometrical configurations of the various solid and liquid phases of real geologic materials.
Field experiments at the U.S. Department of Energy's (DOE) Integrated Field Research Challenge site (IFRC) in Rifle, Colorado (USA) have repeatedly demonstrated the ability of microorganisms to reductively immobilize uranium (U) in U tailings-contaminated groundwater accompanying organic carbon amendment. At the same time, geophysical monitoring during such amendment experiments has proven that Induced Polarization (IP) datasets can provide valuable information regarding geochemical changes induced by stimulated microbial activity, such as precipitation of metallic minerals (e.g. FeS) and accumulation of reactive, electroactive ions (Fe[II]). Based on these findings, we present a novel, modified application of the IP imaging method. Specifically, we utilized an IP characterization approach to delineate areas where fluvially deposited organic material, within aquifer sediments, naturally stimulates the activity of subsurface microflora, leading to both the natural immobilization of uranium and accumulation of reduced end-products (minerals and pore fluids) capable of generating anomalous IP signatures. These so-called 'naturally reduced zones' (NRZ's) are characterized by elevated rates of microbial activity relative to sediments having a lower concentration of organic matter. As noted and based on our previous experiments at the site, the accumulation of metallic minerals represents suitable targets for the exploration with IP tomographic methods. Here, we explore the application of the IP imaging method for the characterization of NRZ's at the scale of the floodplain. We present imaging results obtained through the inversion of 70 independent lines distributed along the floodplain (∼600 sqm). Imaging results are validated through comparisons with lithological data obtained from wells drilled at the site and laboratory analysis of sediment and groundwater samples. Our results show the applicability of the IP method for characterizing regions of the subsurface having a greater propensity for elevated rates of microbial activity, with such regions (themselves often highly localized within a larger sedimentary matrix) exerting an outsized control on contaminant (e.g. U) fate and transport.
Tino Radic
added 14 research items
The Spectral Induced Polarization (SIP) method delivers more important information about the subsoil than the DC-Geoelectric method can. To improve the progress in measurement of the SIP method Multi-Receiver Instruments are used. In addition we have introduced the Multi-Transmitter Technique, from which we expect a further acceleration. As a first step towards routine use, we implemented and tested a novel time series analysis algorithm and expanded the hardware of one of our Multi-Receiver SIP Instruments (type SIP256C, Radic Research) with an additional independent transmitter. Two types of signals were investigated: (a) different frequencies and (b) phase modulation. First results show that both techniques have their individual advantages. The evaluation of a multi-frequency signal is easier, the use of phase-modulated signals seems to allow faster measurements.
Capacitively Coupled Resistivity (CCR) is conventionally used to emulate DC resistivity measurements and may provide important information about the ice content of material in periglacial areas. The application of CCR theoretically enables the determination of both electrical parameters, that is, the resistivity and the electrical permittivity, by analysing magnitude and phase shift spectra. The electrical permittivity may dominate the impedance, especially in periglacial areas or regions of hydrogeological interest. However, previous theoretical work suggested that the phase shift may strongly depend on electrode height above ground, implying that electrode height must be known with great accuracy to determine electrical permittivity. Here, we demonstrate with laboratory test measurements, theoretical modelling and by analysing the Jacobian matrix of the inversion that the sensitivity towards electrode height is drastically reduced if the electrical permittivity is frequency dependent in a way that is typical for ice. For the first time, we used a novel broad-band CCR device 'Chameleon' for a field test located in one of the ridge galleries beneath the crest of Mount Zugspitze. A permanently ice covered bottom of a tunnel was examined. For the inversion of the measured spectra, the frequency dependence of the electrical parameters was parametrized in three different ways: A Debye Model for pure ices, a Cole-Cole Model for pure ices and a dual Cole-Cole Model including interfacial water additionally. The frequency-dependent resistivity and permittivity spectra obtained from the inversion, including low- and high-frequency limits, agree reasonably well with laboratory and field measurements reported in the literature. © The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society.
Katrin Breede
added 4 research items
We analyzed the influence of pore fluid composition on the complex electrical conductivity of three sandstones with differing porosity and permeability. The fluid electrical conductivity (sigma(w)) of sodium and calcium chloride solutions was gradually increased from 25 mS/m to 2300 mS/m. The expected linear relation between sigma(w) and the real component of electrical conductivity (sigma') of the saturated samples was observed. The imaginary component (sigma '') exhibits a steeper increase at lower salinities that flattens at higher salinities. For a glauconitic sandstone and a high porosity Bunter sandstone, sigma '' approaches an asymptotic value at high salinities. Sodium cations result in larger values of sigma '' than calcium cations in solutions of equal concentration. Debye decomposition was used to determine normalized chargeability (m(n)) and average relaxation time (tau) from spectral data. The behavior of sigma '' is comparable to m(n) as both parameters measure the polarizability. At lower salinity, the relation between m(n) and sigma(w) approximates a power law with an exponent of similar to 0.5. The average relaxation time shows only a weak dependence on sigma(w). The normalized chargeability of sandstone samples can be described by the product of the pore space related internal surface and a quantity characterizing the polarizability of the mineral-fluid interface that depends on fluid chemistry. We introduce a new parameter, the specific polarizability, describing this dependence. We propose relations between polarizability and fluid chemistry that could be used to estimate pore space internal surface across samples of varying sigma(w). We observe a consistent maximum polarizability for quartz dominated siliceous material.
Electrical spectral induced polarization (SIP) measurements are increasingly being used in environmental studies of the saturated zone. To better understand the mechanisms causing polarization and to extend the range of SIP applications to the vadose zone, it is important to investigate how the SIP response is affected by water saturation. Therefore, sand and sand-clay mixtures were drained in several steps using a novel measurement set-up allowing SIP measurements with a high accuracy. The measured SIP spectra were interpreted by Debye decomposition, which provided a relaxation time distribution and a chargeability distribution that was converted to a normalized total chargeability. The results showed that the normalized total chargeability of the fully saturated samples increased with increasing clay content due to the larger specific surface area of the clay minerals. Furthermore, normalized total chargeability first increased and then decreased with decreasing saturation for the pure sand and the 5% sand-clay mixture. The normalized total chargeability values for the 10% and 20% sand-clay mixtures only decreased with saturation. The peak relaxation time of the sand-clay mixtures clearly decreased with decreasing saturation. Existing grain-size based mechanistic models for SIP are not able to explain the observed behaviour and the observed relationship between relaxation time and saturation suggests that model concepts relying on polarization processes in the pore space are warranted to explain the measurements on variably saturated porous media presented here.
The prediction capabilities of unsaturated flow and transport models are often limited by insufficient knowledge about the structural and textural heterogeneity of the soil. To obtain more information about soil structure, texture, and heterogeneity, as well as hydraulic properties, noninvasive spectral induced polarization (SIP) measurements have shown promise. However, there clearly is a need for more detailed investigations on the relation between SIP and hydraulic properties, in particular for unsaturated soil. To address this need, we developed a novel experimental setup that allows simultaneous determination of hydraulic and electrical properties. Our setup consists of multi step ouflow equipment for hydraulic measurements and an electrical impedance spectrometer for measurements of the complex electrical conductivity. Two different measurement cells were constructed. The first measurement cell can only be used for nonshrinking soil, while the other one also allows measurements on mildly shrinking soil. Test measurements showed that the measurement accuracy is very high for the complex electrical conductivity. Nonpolarizable point electrodes are used for voltage measurements, ensuring a good contact to the sample for a wide range of water saturations. An experiment performed on unconsolidated sand investigated the dependence of the complex electrical conductivity and fitted Cole-Cole parameters on water saturation. The phase values and chargeability increased with decreasing saturation. The relaxation time associated with a phase peak was independent of saturation and corresponded reasonably to the average grain size of the sand. Therefore, no relationship between relaxation time and unsaturated hydraulic conductivity was found for this well-sorted sand.
Matthias Halisch
added an update
Matthias Halisch
added an update
The logo of our working group, available for all AK IP members.
 
Matthias Halisch
added an update
Today, part of the Working Group IP (AK IP) of the German Geophysical Society (DGG) started this pilot in order to link and reference IP / SIP related research items to one "visible" project folder.
This project is open for all members of the AK IP and administrated by myself and all active collaborators.
 
Tina Martin
added 19 research items
Complex resistivity tomography is presented as an extension of electrical impedance tomography for non-destructive structural tree investigation. Results of laboratory measurements with different frequencies suggest measuring the resistivity and in addition the phase shift at about 0.1 Hz. The measured data are processed using a finite-element-based inversion algorithm, which uses triangular meshes and is thus able to consider any tree shape. We apply the technique to three different oak trees with the aim of fungi detection. Measurements of a healthy tree both in summer and in winter show a ring-shaped structure and indicate a strong seasonal dependence, particularly for the resistivity magnitude. Tomograms on fungi-infected trees clearly show disturbances at the infections at different heights compared with healthy trees. A comparison with tree section photographs shows promising agreement. Moreover, a comparison with measurements at oak-wood samples in the laboratory shows at least partly quantitative coincidence. To conclude, the phase image provides additional information and helps to differentiate disturbances in the cell structure from pure moisture changes. Therefore, the method has the potential to deliver useful additional information, when carried out during routine tree assessment.
Im Rahmen des vom BMBF geförderten Forschungsprojektes ROBEHA wurden u.a. Feldmessungen mit dem Spektral Induzierten Polarisationsverfahrens (SIP) an historischen Schlackenhalden durchgeführt. Ziel dabei ist der zerstörungsfreie und aufwendungsarme Nachweis der vorhandenen Restminerale. So sollen möglichst die verschiedenen Schlackentypen voneinander unterschieden werden können und der Internaufbau der Halde charakterisiert werden. Der Hintergrund dafür ist eine mögliche Rückgewinnung von Metallen aus den Schlacken. Die Ergebnisse der SIP-Feldmessungen zeigten die zu erwartenden hohen Phasenwerte für die Schlacken im Gegensatz zu dem umgebenden Material. Es zeigte sich jedoch auch, dass sich entlang der Profile die Phasensignale der Schlacken hinsichtlich ihrer Stärke und ihrer Form im Frequenzspektrum deutlich unterscheiden. Daher wurden sowohl Lockermaterial-als auch Festgesteinsproben im Feld entnommen und im Labor untersucht. Durch die Labortests konnten die unterschiedlichen SIP Phasensignale bestätigt werden. So variierte das Phasenmaximum für die Lockermaterialproben zwischen 150 und 250 mrad, währenddessen die Festgesteinsproben sogar Werte bis beinahe 700 mrad aufweisen. Auch die Form des Phasenspektrums unterschied sich zum Teil deutlich. Während einige Proben ein Cole-Cole-Verhalten mit einem eindeutigen Frequenzmaximum zeigen, kennzeichnen andere Proben ein bimodales Verhalten mit zwei ausgeprägten Maxima. Aber auch ein " Hängematteneffekt " konnte beobachtet werden. Dabei wird ein Minimum im Phasenspektrum bei Frequenzen zwischen 1 und 100 Hz dadurch sichtbar, dass sich das Phasenmaximum außerhalb des untersuchten Frequenzminimums zu befinden scheint (< 1 mHz) und sich bei hohen Frequenzen (> 1 kHz) die Phasen u.a. aufgrund von EM Effekten erhöhen. Auch die spezifischen Widerstände variieren zwischen wenigen Ωm und 2000 Ωm. Mithilfe der anschließenden petrophysikalischen und mineralogischen Untersuchungen wie BET, Quecksilberporosimetrie, CT, REM und RFA wurde versucht, Korrelationen zwischen den SIP Signalen und der mineralogischen Zusammensetzung der Schlacken zu finden.
Thomas Günther
added 14 research items
We combined two completely different methods measuring the frequency-dependent electrical properties of moist porous materials in order to receive an extraordinary large frequency spectrum. In the low frequency (LF) range, complex electrical resistivity between 1 mHz and 45 kHz was measured for three different soils and sandstone, using the spectral induced polarization (SIP) method with a four electrode cell. In the high frequency (HF) radio to microwave range, complex dielectric permittivity was measured between 1 MHz and 10 GHz for the same samples using dielectric spectroscopy by means of the coaxial transmission line (CTL) technique. The combined data sets cover 13 orders of magnitude and were transferred into their equivalent expressions: the complex effective dielectric permittivity and the complex effective electrical conductivity. We applied the Kramers-Kronig relation in order to justify the validity of the data combination. A new phenomenological model that consists of both, dielectric permittivity and electrical conductivity terms in a Debye- and Cole-Cole type manner was fitted to the spectra. The combined permittivity and conductivity model (CPCM) accounts for the most common representations of the physical quantities with respect to the individual measuring method. A maximum number of four relaxation processes was identified in the analysed frequency range. Amongst these are the free water and different interfacial relaxation processes, the Maxwell-Wagner effect, the counterion relaxation in the electrical double layer and the direct-current electrical conductivity. There is evidence that free water relaxation does not affect the electrical response in the SIP range. Moreover, direct current conductivity contribution (bulk and interface) dominates the losses in the HF range. Interfacial relaxation processes with relaxations in the HF range are broadly distributed down to the LF range. The slowest observed process in the LF range has a minor contribution to the HF response.
Low-frequency field and laboratory induced polarization measurements are carried out to characterize the hydrogeological conditions at Schillerslage test site in Germany. The laboratory spectral induced polarization (SIP) data are analyzed to derive an empirical relationship for predicting the hydraulic conductivity (K) in the field scale. On the other hand, the results from SIP sounding and profiling field data indicate that the method identifies the lithological layers with sufficient resolution to achieve our objectives. Two main Quaternary groundwater aquifers separated by a till layer can be well differentiated. Furthermore, the phase images are also capable of monitoring thin peat layers within the sandy groundwater aquifer. However, the field results show limitations of decreasing resolution with depth and/or low data coverage. Similarly, the SIP laboratory results show a certain shift in SIP response due to different compaction and sorting of the samples. The overall results obtained show that the integration of field and laboratory SIP measurements is an efficient tool to avoid a hydrogeological misinterpretation. In particular, two significant but weak correlations between individual real resistivities (ρ') and relaxation times (τ), based on a Debye decomposition (DD) model, with measured K are found for the upper groundwater aquifer. While the maximum relaxation time (τmax) and logarithmically weighted average relaxation time (τlw) show a better relation with K values than the median value τ50, however, the single relationships are weak. A combined power law relation between individual ρ' and/or τ with K is developed with an expression of A · (ρ')B · (τlw)C, where A, B and C are determined using a least-squares fit between the measured and predicted K. The suggested approach with the calculated coefficients of the first aquifer is applied for the second one. The results indicate a good correlation with the measured K and prove to be superior to single phase angle models as the Börner or Slater models.
Matthias Halisch
added a research item
The relaxation phenomena observed in the electrical low-frequency range (approximately 1 MHz-10 kHz) of natural porous media such as sandstones are often assumed to be directly related to the dominant (modal) pore throat sizes measured, for instance, with mercury intrusion porosimetry. Attempts to establish a universally valid relationship between pore size and peak spectral induced polarization (SIP) relaxation time have failed, considering sandstones from very different origins and featuring great variations in textural and chemical compositions as well as in geometric pore space properties. In addition working with characteristic relaxation times determined in Cole-Cole or De-bye decomposition fits to build the relationship have not been successful. In particular, samples with narrow pore throats are often characterized by long SIP relaxation times corresponding to long "characteristic length scales" in these media, assuming that the diffusion coefficients along the electrical double layer were constant. Based on these observations, three different types of SIP relaxation can be distinguished. We have developed a new way of assessing complex pore spaces of very different sandstones in a multimethodical approach to combine the benefits of mercury intrusion porosimetry, micro-computed tomog-raphy, and nuclear magnetic resonance. In this way, we achieve much deeper insight into the pore space due to the different resolutions and sensitivities of the applied methods to pore constrictions (throats) and wide pores (pore bodies). We experimentally quantify pore aspect ratios and volume distributions within the two pore regions. We clearly observe systematic differences between three SIP relaxation types identified previously , and we can attribute the SIP peak relaxation times to measured characteristic length scales within our materials. We highlight selected results for a total of nine sandstones. It seems that SIP relaxation behavior depends on the size difference of the narrow pore throats to the wide pore bodies, which increases from SIP type 1 to type 3.
Matthias Halisch
added a project goal
- exchange of information on research and experience with IP and SIP
- development of standards and reference materials
- collecting ideas for further work and projects
- disseminate the knowledge on IP
This project site is supposed to increase the visibility of IP / SIP related research and according publications. The working group is open to everyone for active or passive membership.