Induced Polarization Effects Research Articles

Airborne Inductive Induced Polarization Chargeability Mapping of VTEM Data

SUMMARY Airborne inductive induced polarization (AIIP) effect has been widely recognized in airborne time domain EM system data. AIIP chargeability mapping opens new and exciting areas in mineral exploration for airborne time domain EM systems in the search for sulphides and clay minerals. An AIIP chargeability mapping tool based on CSIRO/AMIRA Airbeo is created for VTEM data, with examples from Mt Milligan, British Columbia, Canada and Tullah, Tasmania. Using the Cole-Cole frequency dependent resistivity, the tool examines the VTEM decay data spectrally and selects the decay associated with the lowest RMS error from a set of decays generated by varying chargeability m and time constant within specific ranges, giving a constant frequency factor c, while the background resistivity is inverted. The parameter mo used to generate the decay is the AIIP apparent chargeability.

The Role of the Amino Protecting Group during Parahydrogenation of Protected Dehydroamino Acids.

A series of dehydroamino acids endowed with different protective groups at the amino and carboxylate moieties and with different substituents at the double bond have been reacted with parahydrogen. The observed ParaHydrogen Induced Polarization (PHIP) effects in the (1)H NMR spectra are strongly dependent on the amino protecting group. DFT calculations allowed us to establish a relationship between the structures of the reaction intermediates (whose energies depend on the amido substitution) and the observed PHIP patterns.

Quantifying Airborne Induced Polarization effects in helicopter time domain electromagnetics

This paper derives the Airborne Induced Polarization (AIP) response of an airborne electromagnetic (AEM) system to a horizontal, thin sheet conductor. A vertical component double-dipole approximates helicopter systems with towed concentric horizontal transmitter and receiver loops in frequency- or time-domain. In time domain, the AIP effect typically shows up as late-time negative data with amplitude 4 to 5 orders of magnitude smaller than the early-time peak of the positive AEM responses. Because of limited bandwidth from the short sample time after the decay of inductive responses, accurate extraction of intrinsic AIP parameters other than a minimum chargeability is almost impossible. Modelling further suggests that AIP effects in double-dipole AEM systems can only be reliably detected from polarizable material in the top few tens of metres. A titanium mineral exploration case history from the Lac Brûlé area, Quebec, Canada illustrates strong spatial coherence of AIP minimum chargeability estimates and their independence from other effects such as conductivity and magnetic susceptibility.

Induced polarization effect in reservoir rocks and its modeling based on generalized effective-medium theory

One of the major tasks of the petroleum resource-efficient technologies (pREFFIT) is the development and improvement of the methods of exploration for energy resources. This review paper summarizes the results of the research on induced polarization (IP) effect in reservoir rocks conducted by the University of Utah Consortium for Electromagnetic Modeling and Inversion (CEMI) and TechnoImaging. The electrical IP effectin hydrocarbon (HC) bearing reservoir rocks having nonmetallic minerals is usually associated with membrane polarization, which is caused by a variation in the mobility of the ions throughout the rock structure. This mobility is related to the size and shape of the pores filled with electrolyte and the double electrical layers. We have studied the IP response of multiphase porous systems by conducting complex resistivity (CR) frequency-domain IP measurements for two different groups of samples: sands and sandstones containing salt water in pores and those whose unsaturated pores were filled with synthetic oil.We have also studied selected carbonate reservoir formations, typical of some major HC deposits. The generalized effective-medium theory of induced polarization (GEMTIP) was used to analyze the IP parameters of the measured responses. This paper presents a conceptual model of polarizing clusters to explain the observed IP phenomena. The results of this study show that the HC bearing sands and sandstone samples and carbonate rocks are characterized by a significant IP response. These experimental observations, compared with the theoretical modeling based on the GEMTIP approach, confirm earlier geophysical experiments with the application of the IP method for HC exploration.

Induced polarization effect in reservoir rocks and its modeling based on generalized effective-medium theory

One of the major tasks of the petroleum resource-efficient technologies (pREFFIT) is the development and improvement of the methods of exploration for energy resources. This review paper summarizes the results of the research on induced polarization (IP) effect in reservoir rocks conducted by the University of Utah Consortium for Electromagnetic Modeling and Inversion (CEMI) andTechnoImaging.The electrical IP effect in hydrocarbon (HC) bearing reservoir rocks having nonmetallic minerals is usually associated with membrane polarization, which is caused by a variation in the mobility of the ions throughout the rock structure.This mobility is related to the size and shape of the pores filled with electrolyte and the double electrical layers. We have studied the IP response of multiphase porous systems by conducting complex resistivity (CR) frequency-domain IP measurements for two different groups of samples: sands and sandstones containing salt water in pores and those whose unsaturated pores were filled with synthetic oil. We have also studied selected carbonate reservoir formations, typical of some major HC deposits. The generalized effective-medium theory of induced polarization (GEMTIP) was used to analyze the IP parameters of the measured responses. This paper presents a conceptual model of polarizing clusters to explain the observed IP phenomena. The results of this study show that the HC bearing sands and sandstone samples and carbonate rocks are characterized by a significant IP response. These experimental observations, compared with the theoretical modeling based on the GEMTIP approach, confirm earlier geophysical experiments with the application of the IP method for HC exploration. © 2015 Tomsk Polytechnic University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer review under responsibility of Tomsk Polytechnic University.

Environmental applications of the IP method: Surveys of subsurface waste

Induced-polarization (IP) effects in electrical geophysical surveys have been used in mineral-exploration projects for many decades, but only in the past 15 years or so has IP in environmental geophysics become a more common, commercially applicable method. This is primarily because of improvements in the economics of the technique and in data quality resulting from equipment advances. One field of environmental applications in which the IP method has been particularly useful is the study of buried waste. In the past, IP data acquisition was relatively expensive, and as a result, many landfill IP surveys were limited in scope for budgetary reasons. With the improving economics of the method, however, extensive amounts of data have been acquired at more than 50 landfills. At one site alone, 95 lines of IP and resistivity data were acquired, and at another, more than 14,000 transmitter-receiver pairs were used. Examination of this large, diverse data set allows several interesting general conclusions to be drawn that were not evident from the more limited surveys in the past. For example, early interpretations of IP results over landfills assumed that the IP effect was primarily the result of metallic debris in the waste. However, from the large database over many landfills, it appears that multiple sources of the IP effect are associated with the waste, and IP anomalies are clearly evident over landfills that contain little or no metal. It is also clear that IP surveys are substantially more reliable than other more traditional waste-mapping methods such as resistivity (or its inverse, conductivity) and magnetics. In addition, comparisons of data sets over time suggest that the IP method might be a useful tool in monitoring the degradation of subsurface waste.

Spectral-induced polarization characteristics of rock types from the skarn deposit in Gagok Mine, Taebaeksan Basin, South Korea

Spectral-induced polarization (SIP), which measures the responses to alternative current of multi-frequencies below 1 kHz, is an excellent technique for exploring the economic minerals in the ore deposits. However, the studies on the SIP characteristics of rocks from ore deposits have rarely been conducted due to the decline of mining activities. For effective exploration, the SIP responses of in situ rocks should be recognized first. Therefore, this study was conducted to understand the characteristics of the SIP responses depending on the rock type using the laboratory measurements. Rock samples were obtained from both host rocks and skarn rocks in the Gagok Mine which is a typical skarn deposit in South Korea. The responses of the host rocks, which include dielectric minerals, were found to depend on the induced polarization (IP) effect of the compact layer. In contrast, the responses of the skarn rocks, which were mixtures of dielectric and metallic minerals, depended on the IP effect of the diffuse layer. This study clearly demonstrates that SIP responses are determined by the electrochemical characteristics of the composing minerals.

Elucidating factors important for monovalent cation selectivity in enzymes: E. coli β-galactosidase as a model.

Many enzymes require a specific monovalent cation (M(+)), that is either Na(+) or K(+), for optimal activity. While high selectivity M(+) sites in transport proteins have been extensively studied, enzyme M(+) binding sites generally have lower selectivity and are less characterized. Here we study the M(+) binding site of the model enzyme E. coli β-galactosidase, which is about 10 fold selective for Na(+) over K(+). Combining data from X-ray crystallography and computational models, we find the electrostatic environment predominates in defining the Na(+) selectivity. In this lower selectivity site rather subtle influences on the electrostatic environment become significant, including the induced polarization effects of the M(+) on the coordinating ligands and the effect of second coordination shell residues on the charge distribution of the primary ligands. This work expands the knowledge of ion selectivity in proteins to denote novel mechanisms important for the selectivity of M(+) sites in enzymes.

Assessment of soil salinity using electrical resistivity imaging and induced polarization methods

2D imaging involving geoelectrical resistivity and time domain induced polarization has been used to assess the spatial variability of the physical properties of subsurface soil in Covenant University Farm, southwestern Nigeria. Apparent resistivity and chargeability of the induced polarization effect were concurrently measured along six traverses using Wenner array. The observed data were processed to produced 2D inverse models of the subsoil resistivity and chargeability. Soil samples were also collected and analysed for conductivity and salinity levels. The results show that the salinity level in the soil is within the range for normal soil and therefore healthy for plant growth. The inverse model sections were integrated with the laboratory test to qualitatively assess the salinity, degree of compaction, and thickness of the soil in the farm. Other petrophysical properties such as clay volume, moisture content and organic matter which are related to soil conductivity were also inferred. The study demonstrates that geoelectrical resistivity imaging can be a useful tool for effectively assessing the variations of soil condition in large tracts of land for precision agriculture. Key words: Soil salinity, 2D imaging, geoelectrical resistivity, induced polarization, precision farming.

Three-dimensional modeling of IP effects in time-domain electromagnetic data

Understanding the effects of induced-polarization (IP) effects on time-domain electromagnetic data requires the ability to simulate common survey techniques when taking chargeability into account. Most existing techniques preform this modeling in the frequency domain prior to transforming their results to the time domain. Even though this technique can allow for chargeable material to be easily incorporated, its application for some problems can be computationally limiting. We developed a new technique for forward modeling the time-domain electromagnetic response of chargeable materials in three dimensions. The frequency dependence of Ohms’ law translates to an ordinary differential equation when considered in the time domain. The system of ordinary-partial differential equations was then discretized using an implicit time-stepping algorithm, that yielded absolute stability. This approach allowed us to operate directly in the time domain and avoid frequency to time-domain transformations. Although this approach can be applied directly to materials exhibiting Debye dispersions, other Cole-Cole dispersions resulted in fractional derivatives in time. To overcome this difficulty, Padé approximations were used to represent the frequency dependence as a rational series of integer order terms. The resulting method was then simplified to generate a reduced time-domain model that can be used to forward model the IP decay curves in the absence of any electromagnetic coupling. We found numerical examples in which the method produced accurate results. The potential application of the method was demonstrated by modeling the full time-domain electromagnetic response of a gradient array IP survey, and the occurrence of negative transients in airborne time-domain electromagnetic data.

Observation Frequency Selection Based on Dynamic and Electric Field Excitation Method for Advanced Detection in Coal Mine Roadway

The dynamic and electric field excitation method is a new advanced detection method. In this method, the observation frequency and of emission electrode must be reasonably selected according to the actual geological conditions of coal mine roadway to obtain the apparent frequency with adequate Induced Polarization (IP) information of geological anomalies and improve the measurement accuracy of the instrument. This paper completed the simulation of apparent frequency varying with the observation frequency and Cole-Cole model parameters with MATLAB software. The results show that the key to selecting the observation frequency mainly depends on the charge and discharge time constant .Then the paper analyzed the effect of the measured apparent frequency on the measurement accuracy. According to time constant values​​ of geological conditions in coal mine roadway, considering the efficiency and electromagnetic coupling effects on the measurement, it is best to select the observation frequency within a frequency range of 0.05~0.1Hz and the frequency ratio coefficient of 13 or 15. Now apparent IP effect is obtained.

The sensitivity analysis of different induced polarization models used in magnetotelluric method

The magnetotelluric signal is a comprehensive response composed of electromagnetic induction and induced polarization (“IP effect”). The extracting of the IP response from MT signal is not only beneficial for improving the accuracy of MT exploration, but also the acquired IP effect can provide us with unique information about underground structure. There are many models proposed through laboratory measurements by some researchers to approximately describe the IP effect, and yet which model is comparatively proper and effective for the use in MT method is still unknown. Besides, due to the weakness of the induced polarization effect, it is a tough question when separating one from another in practical exploration. The main objective of this paper is to choose an IP model that is best suited for the manipulation in MT forward and inversion by calculating and analyzing the sensitivity and integrated sensitivity of apparent resistivity to the different IP model parameters. The analysis of these results offers some useful suggestions when selecting the IP model in MT method, and meanwhile the application range of IP method is expanded.

Experimental Study of Induced Polarization Effect in Unconventional Reservoir Rocks

Unconventional hydrocarbon reserves substantially surpass those of conventional resources and therefore are extremely economically attractive. However, exploration and production of uncon-ventional reserves is challenging. This paper demonstrates that one can observe significant induced polarization effects in shale reservoir rocks, which can be used in exploration for unconventional reserves. The generalized effective-medium theory of induced polarization (GEMTIP) was used to model the complex resistivity of shale rocks. We demonstrate that GEMTIP modeling provides an evaluation of mineral composition and volume fractions in rock samples. We have conducted spectral induced polarization (IP) measurements using different types of shale rocks to test the feasibility of the IP method and GEMTIP modeling for studying unconventional hydrocarbon (HC) reservoir rocks.

Induced Dipoles Incorporated into All-Atom Zn Protein Simulations with Multiscale Modeling

Zinc is found saturated in the deposited Amyloid-beta (Aβ) peptide plaques in Alzheimer's disease (AD) patients' brains. Binding of zinc promotes aggregation of Aβ, including the pathogenic aggregates. Up to now, only the region 1-16 of Aβ complexed with zinc (Aβ(1-16)-Zn) is defined structurally in experiment. In order to explore the induced polarization effect of zinc on the global fluctuations and the experimentally observed coordination mode of Aβ(1-16)-Zn, we consider an all-atom molecular dynamics (MD) of Aβ(1-16)-Zn solvated in implicit water. In our model, the zinc polarization affects the whole peptide. The induced dipoles are divided into three distinct scales according to their distances from zinc. Besides, the atomistic polarizability on the coordinating side chains is rescaled to describe the electron redistribution effect. We show that, associated with proper van der Waals (vdW) parameters, our model not only obtains the reasonable coordinating configuration of zinc binding site but also retains the global stabilization, especially the N-terminal region, of the Aβ(1-16)-Zn. We suggest that it is the induced polarization effect that promotes reasonable solvent exposures of hydrophobic/hydrophilic residues regarding zinc-induced Aβ aggregation.

On the estimation of the maximum depth of investigation of transient electromagnetic soundings: the case of the Vizcaino transect, Mexico

We test an approach proposed in the literature for estimating the maximum depth of investigation (MDI) of in-loop transient electromagnetic soundings (TEM) with data from the Vizcaino transect, a profile of 38 TEM soundings crossing the Baja California peninsula. The validity of this approach is confirmed by comparing the MDI with the deepest interface of 16 stratified models. In these soundings, all located over the Vizcaino basin, the measured data are not affected by induced polarization. The models indicate the presence of a dipping conductor interpreted as a zone of seawater intrusion with a large lateral extension of over 70 km. The remaining 22 soundings, located over igneous and metamorphic rocks, show reversals in the voltage polarity, indicating the presence of induced polarization effects. The layered Cole-Cole models for these soundings suggest a significant decrease in the MDI. This is confirmed by analyzing the depth behavior of the subsurface current densities. We further analyze the noise level of a data set comprising close to 2000 late-time voltages of about 400 TEM sites acquired in northwestern Mexico. No difference was found between the stationary noise levels of winter and summer, presumably because near thunderstorms are practically absent in this part of Mexico.

Inductive source induced polarization

Induced polarization (IP) surveys are commonly performed to map the distribution of electrical chargeability that is a diagnostic physical property in mineral exploration and in many environmental problems. Although these surveys have been successful in the past, the galvanic sources required for traditional IP and magnetic IP (MIP) surveys prevent them from being applied in some geological settings. We develop a new methodology for processing frequency domain EM data to identify the presence of IP effects in observations of the magnetic fields arising from an inductive source. The method makes use of the asymptotic behaviour of the secondary magnetic fields at low frequency. A new quantity, referred to as the ISIP datum, is defined so that it equals zero at low frequencies for any frequency-independent (non-chargeable) conductivity distribution. Thus, any non-zero response in the ISIP data indicates the presence of chargeable material. Numerical simulations demonstrate that the method can be applied even in complicated geological situations. A 3-D inversion algorithm is developed to recover the chargeability from the ISIP data and the inversion is demonstrated on synthetic examples.

Induced polarization in airborne EM

A major impediment in the path toward airborne induced polarization (IP) is an effective method to quantify data from inductive sources, such as those used in airborne electromagnetic systems. We modeled inductive IP using a combination of Warburg and exponential decay models as a basis for fitting electromagnetic data from ground time-domain electromagnetic (TEM) and airborne versatile TEM (VTEM) surveys. Observed decays were deconvolved into electromagnetic and IP constituents by constrained least-squares fitting of basis functions modified to account for transmitter waveforms. The method was confirmed through synthetic modeling of 2D and 3D structures, and when applied to ground TEM or airborne TEM data, obtained an estimate of apparent chargeability at each station or fiducial. In the case of a VTEM survey in Africa, the apparent chargeabilities mapped graphitic sediments and provided spatially consistent indications of clay concentrations. A limitation on this airborne IP for airborne applications is motion noise, which places a lower limit on usable base frequency and begins to significantly affect the signal at the later delay times, when IP effects are most visible.

Numerical optimization of carrier confinement characteristics in (AlxGa1−xN/AlN)SLs/GaN heterostructures

Abstract We present numerical optimization of carrier confinement characteristics in (AlxGa1−xN/AlN)SLs/GaN heterostructures in the presence of spontaneous and piezoelectrically induced polarization effects. The calculations were made using a self-consistent solution of the Schrodinger, Poisson, potential and charge balance equations. It is found that the sheet carrier density in GaN channel increases nearly linearly with the thickness of AlN although the whole thickness and equivalent Al composition of AlxGa1−xN/AlN superlattices (SLs) barrier are kept constant. This result leads to the carrier confinement capability approaches saturation with thicknesses of AlN greater than 0.6 nm. Furthermore, the influence of carrier concentration distribution on carrier mobility was discussed. Theoretical calculations indicate that the achievement of high sheet carrier density is a trade-off with mobility.

Para‐hydrogen induced polarization of Si‐29 NMR resonances as a potentially useful tool for analytical applications

Para-hydrogen-induced polarization effects have been observed in the (29)Si NMR spectra of trimethylsilyl para-hydrogenated molecules. The high signal enhancements and the long T(1) values observed for the (29)Si hyperpolarized resonances point toward the possibility of using (29)Si for hyperpolarization applications. A method for the discrimination of multiple compounds and/or complex mixtures of hydroxylic compounds (such as steroids), consisting of the silylization of alcoholic functionalities with an unsaturated silylalkyl moiety and subsequent reaction with para-H(2), is proposed.

Fast-decaying inductively induced polarization in frozen ground: A synthesis of results and models

article i nfo Many TEM data from Yakutia and other areas of widespread permafrost bear a manifestation of the induced polarization (IP) effect. The distinguishing feature of this effect is the distortion in the monotony, sign rever- sals included TEM voltage responses in the time range from a few tens to a few hundreds of microseconds. According to the inversion of TEM responses in terms of the Cole-Cole conductivity model, the IP effects are produced by fast decaying polarization in the upper 100 m of frozen ground. Shallow frozen rocks exhibit the chargeability m in the range 0.2 to 0.85, mostly within 0.2-0.5, the relaxation time τ from 35 to 250 μs (50 to 100 μs on average). As for the exponent c, it is usually in the range 0.8 to 1, which is evidence of a narrow range of the relaxation times. Conversion of chargeability into low-frequency dielectric permittivity gives values of the order of tens or a few hundreds of thousands. These very high permittivities cannot be explained by dielectric relaxation of ice inclusions and/or interfacial polarization. A more likely reason is elec- trochemical polarization of the films of unfrozen water on the mineral grain and ice inclusion surfaces. It is convenient to interpret the electrochemical polarization effects in terms of frequency-dependent surface conductivity controlled by the surface-to-volume ratio. For an unfrozen wet rock the surface conductivity is small compared to the bulk conductivity of the pore water. However, upon freezing the pore water, the sur- face conductivity becomes dominant which results in the manifestation of IP phenomena. An additional rea- son why freezing of a wet porous rock is favorable for the manifestation of IP effects in TEM data is that the relative contribution of eddy currents becomes less than that of polarization ones.