Geoelectric Model Research Articles

Ultra-complex Geological Anomalies Modeling on Transient Electromagnetic Response

In reality, the spatial distribution of geological anomalies is extremely complex. In the process of numerical simulation of transient electromagnetic method, limited to the modeling level, regular sphere, cylinder, cuboid and other simple models are often used to replace the complex actual geological model. As a result, there is a large deviation between the numerical simulation results and the real transient electromagnetic response of the actual geological model, which affects the reliability of the data interpretation. In order to solve the problem of transient electromagnetic numerical simulation of complex geoelectric model, we established complex geological anomalies model based on a variety of modeling platforms, and integrated the spatial combination information of nodes, lines and surfaces of the model with the spatial information of the observation system. Then gained the unstructured mesh discrete space of the integrated model according to the Delaunay tetrahedral subdivision principle. Finally, we realized the simulation of the transient electromagnetic responses of ultra-complex models by using vector finite element method.

Fine grid model for the dielectric characteristics of ground‐penetrating radar in mixed media

ABSTRACTThe Fisher–Yates random shuffling algorithm combined with the finite‐difference time‐domain method is proposed to construct a fine grid model for the forward simulation of ground‐penetrating radar in mixed media. First, the finite‐difference time‐domain method was used to divide the coarse grid model into several fine grid models by conforming to the boundary conditions of different media, and the corresponding dielectric parameters were assigned to Yee cells in each fine grid model. Then, the Fisher–Yates random shuffling algorithm was used to randomly scramble all Yee cells with equal probability, and the array of scrambled Yee cells was recombined into a coarse grid model. Finally, the geoelectric model of mixed media was generated with the finite‐difference time‐domain method, and a ground‐penetrating radar image excited by electromagnetic wave pulses was obtained. To explore the characteristic signals and dielectric properties of the ground‐penetrating radar electromagnetic response in mixed media, image entropy theory was used to describe the ground‐penetrating radar image, and waveform analysis and wavelet transform mode maximum methods were used to analyse the single‐channel ground‐penetrating radar signal of the mixed media. The results showed that the Fisher–Yates random shuffling–finite‐difference time‐domain method can be used to construct a valid and stable fine grid model for simulating ground‐penetrating radar in mixed media. The model effectively inhibits electromagnetic attenuation and energy dissipation, and the wavelet transform mode maximum method explains the relative dielectric permittivity distribution of the mixed media. The findings of this study can be used as a theoretical basis for correcting radar parameters and interpreting images when ground‐penetrating radar is applied to mixed media.

Geoelectrical Models of the Achimov Formation Reservoirs at the Tevlinsko-Russkinskoye Field

The article discusses the results of applying the methodology for assessing the oil saturation of the Achimov formation reservoirs based on the quantitative interpretation of electric logging data in vertical wells of the Tevlinsko-Russkinskoye field. Interpretation of electric logging data using traditional methods leads to errors in oil saturation estimation due to complex diagram shapes, which make it difficult to take readings in thin layers under the influence of resistivity-contrasting zones of penetration and enclosing layers. To calculate reservoir properties, approved petrophysical dependencies were applied, and the resistivity value of thin reservoirs was determined as a result of numerical joint inversion of data from a complex of galvanic and induction probes in the class of 2D geoelectric models, taking into account the design features of probes, well structure, radial and vertical distribution of electrophysical properties of rocks in the section. In 24 wells, geoelectric models were built and the oil content of the BS reservoirs was estimated.

Substantiation of the geoelectric model of the freshwater reservoir in the water areas

The relevance of the search for fresh water exists for large areas of the planet. Often arid regions are washed by saline reservoirs, under the waters of which lie significant volumes of fresh water. To search for these waters, it is rational to use aquatic methods of electrical exploration. The substantiation of the geoelectrical model of a freshwater reservoir in offshore areas for numerical modeling of an electrical survey signal at direct current and during a transient process is given. The result of the study shows the rationality of using electrical exploration methods for the search and exploration of freshwater reservoirs in the water areas.

Geophysical research on the IGAN Glacier in 2021

The results of radar studies of the IGAN glacier carried out in 2019 and 2021 are presented in the paper. Measurements of the thickness of the snow cover and ice were carried out using the PICOR-LED GPR (1600 MHz) and VIRL-7 (20 MHz), respectively. Studies have revealed significant winter snow accumulation on the glacier and its stable spatial distribution, and also showed a significant ice thickness (up to 106 m) and the polythermal structure of the glacier. Electrotomography was used to monitor the central part of the glacial moraine. Two-dimensional geoelectric sections and a three-dimensional geoelectric model of the internal structure of the moraine are constructed. The size of the rock-ice core (high-resistance rocks) increases towards the center of the moraine, nevertheless, there is an active degradation of frozen material in the marginal parts of the moraine.

Interactive software for processing and modeling oil well resistivity logs as part of a two-dimensional interpretation approach

Resistivity well logging is widely used to identify reservoir rocks and evaluate their oil potential. However, the integral nature of the rock response to the field excited by the logging tool leads to the fact that the tool signal opposite the target formation is influenced by a well filled with drilling fluid, overlying sediments, drilling fluid filtrate invasion into the formation, etc. Today's widespread methods of resistivity logs interpretation are based on excessive simplifications, which in complex conditions leads to errors in determining the oil saturation coefficient of the target reservoir, costs of testing water-saturated intervals and missing the potentially promising reservoirs. The paper presents the results of developing new interactive software for working with well logging data and geoelectric model of the environment, focused on a 2D approach to interpreting resistivity logs. The use of a 2D axisymmetric geoelectric model of the medium as a base allows one to correctly take into account the above factors when interpreting practical data. Original realization of user interaction with geoelectric model of near-wellbore space takes into account the features of 2D approach to resistivity logs interpretation and provides convenience of work with multilayer models. The computing server AlondraCore integrated with the software supports resistivity logs simulation using two types of forward problem solvers: high-precision finite-element and fast neural network-based ones. The finite-element algorithms provide high log simulation accuracy with the ability to adjust the tool parameters. On the other hand, the neural network-based algorithms provide fast solution of forward problems for common logging tools.

Electrical resistivity tomography for characterization of carbon-rich rocks (shungites)

Electrical resistivity tomography (ERT) is rightly considered an effective tool for studying subsurface, but some particular geological conditions can lead to results that are difficult to explain. Carbon-rich rocks undoubtedly belong to such cases because of their very high resistivity contrast compared to the host rock. Shungite-bearing rocks have total organic carbon (TOC) in the range of 5 to 95 weight percentage (wt%), and such a range accounts for a wide variety of electrical rock properties. We used ERT at three shungite deposits to study their internal structure and to evaluate the reliability of the resulting geoelectrical models. The study of carbon-rich rocks (shungites) of the Zaonega Formation in the Onega basin is interesting in the Precambrian carbon accumulation and the exploration of shungite deposits. As a result, we clarified the main features of geological sections, such as topsoil base, primary shungite-rich successions, individual zones of metasomatic rocks, and gabbro intrusions. Drilling data and geological reference sections show the reliability of the ERT cross-sections and accuracy of main geological boundaries with an average discrepancy of 1–2 m. Laboratory studies of drill cores samples revealed the nonlinear relationship between resistivity and TOC, which, in the future, may facilitate identifying rocks with relatively low carbon. However, it was impossible to quantitatively assess TOC by ERT models due to the resolution-dependent correlation loss. Comparison of synthetic model with natural field one shows that the significant considerable contrast of resistivity for geological layers about 1:1000 ratio and more produces lower sensitivity and higher uncertainty parts of the inverse models. At the same time, despite high RMS errors, all obtained models retain their geological validity. Our research results demonstrate the efficiency of ERT for mineral exploration of shungites and reveal its internal limitations when the survey these specific highly conductive carbon-rich rocks.

Investigation of the structural control of a deltaic valley with geophysical methods. The case study of Pineios river delta (Thessaly, Greece)

The current study aims to clarify the structural regime of the deltaic valley of Pineios river (Thessaly, Greece). The structural control of a deltaic area is usually a crucial parameter for its Palaio-geographical evolution and the latter needs to be clear for the contemporary conservation of such a sensitive ecotope environmentally. The investigation of the concealed subsurface tectonic structures was accomplished through the combined interpretation of gravity measurements, VES and TEM soundings. The standard gravity data reduction has been carried out and the residual anomaly was isolated with the contribution of the Fourier filters. The Euler deconvolution has been applied, providing the corresponding depth solutions between 159.8 and 1716.6 m. In the context of the qualitative interpretation, we produced several structural maps (THDR, VDR, Tilt and Theta) in order to enhance the edges of density sources that may reflect fault zones. Severe indications for the delineation of fault zones of the area were provided by these maps. Moreover, 3D density models of the area have been constructed illustrating the subsurface density distribution, up to depths of 3370 m. A main zone of lower densities in the central part of the delta has been revealed, surrounded by three zones of higher densities. Afterwards, the densities of the majority of the existing geological formations were determined with laboratory measurements from geological specimens. Therefore, three geophysical-geological profiles have been constructed, based not only on the gravity modelling but also on the geological interpretation of the geoelectrical layered models from the VES and TEM measurements. In conclusion, concealed and unknown tectonic structures of the Pineios deltaic valley have been identified beneath the surface.

3D marine controlled-source electromagnetic modeling using an edge-based finite element method with a block Krylov iterative solver

Abstract An edge-based finite element method for the numerical modeling of electromagnetic fields in complex media is presented. We used the analytical solution on an electric field in a homogeneous half space to develop a source correct factor to reduce the influence of source singularity and boundary conditions on the numerical accuracy, so that we can minimize the time required to construct the field source term in the scattered field formula. The modeling domain was discretized using an unstructured tetrahedral mesh. We transformed the complex equations of the electrical field into two real-valued equations by decomposing the field into real and imaginary components. Thereafter, we adopted a block conjugate orthogonal conjugate gradient (BL_COCR) iterative solver with an incomplete LU decomposition preconditioner, which was robust for ill-conditioned systems and efficient for multiple source electromagnetic modeling to solve the real-valued equation systems. Using the analytical solution on an electric field in a homogeneous layer model, we evaluated the accuracy of our numerical forward solution and the results showed that the source correct factor can reduce forward modeling errors associated with boundary effects and source singularities. We also applied the developed algorithm to compute the CSEM responses for typical 3D marine geo-electric models with different number of sources and compared with different iterative solvers, and the results showed that the BL_COCR solver has high computational efficiency when solving multiple right-hand term problems.

Geophysical and Hydrochemical Studies to Map Saltwater Infiltration into Freshwater aquifers: A case study of Ikoyi, Lagos State, Nigeria

A total of three electrical imaging lines were measured using the Wenner configuration. And a total of fifteen VES was carried out within the area of investigation and six water samples was collected. The results were presented as profiles, model sections, inverted sections and tables. Interpretations of these results involve both qualitative and quantitative deductions from 1D and 2D geoelectric models and laboratory analysis for the water analysis. The VES data were processed by partial curve matching to generate the 1st order geoelectric parameters and inverted in 1D using the WinResist. The 2D resistivity data were processed by inversion using the DIPROFWIN to generate the 2D resistivity section across each traverse while the water samples were taken to the laboratory for comprehensive analysis. The 2D resistivity structures reveal the lateral and the vertical subsurface information with resistivity values ranging from 0.130 to 4741 Ωm. The resistivity values are representative of the clay, clay (saline), clayey sand (saline), clayey sand and sand. From the quantitative interpretation five to six distinct layers were identified. The layers are: topsoil, clayey sand, clay, saline clayey sand, saline clay and sand. The resistivity of the topsoil varies from 38.2 Ωm to 155.3 Ohm-m. The resistivity of the sand varies from 100.8 Ωm to 115.8 Ωm. The resistivity of clayey sand varies from 56.6 Ωm to 90.1 Ωm. The resistivity of clay varies from 12.7 Ωm to 41.2 Ωm. The resistivity of the saline layer (saline clayey sand/clay) varies from 2.1 Ωm to 51.2 Ωm. The depth of saline clay interface varies from 25.7 m to 72.6 m. The depth to the saline clayey sand interface varies from 25.7 - 72.6 m. The chemical analysis of water samples showed that the pH varies from 7.05 to 8.42, total dissolved solids vary from 1786 to 2116 mg/L and electrical conductivity varies from 2106 to 2656 µS/cm. The anions and cation concentrations such as Ca2+, Mg2+, Na+, K+, Cl- and HCO3- ranges from 158 to 185 mg/L, 36 to 48 mg/L, 222 to 287 mg/L, 3.2 to 3.8 mg/L, 10.86 to 20.87 mg/L and 2.33 to 3.88 mg/L respectively. The ratio of Cl/HCO3- ion ranges from 4.05 to 7.67. The interpreted results show saline water intrusion where they occur in different part of the area investigated. The results showed the effectiveness and usefulness of electrical resistivity method in mapping saline water intrusion problem in coastal areas. However, it is necessary to carry out integrated geophysical surveys involving electrical resistivity and induced polarization methods prior to drilling in the study area.

Geometric 3-D inversion of airborne time-domain electromagnetic data with applications to kimberlite pipes prospecting in a complex medium

We consider an approach to solving 3-D inverse problems of airborne time-domain electromagnetic (TD-EM) survey in complex geoelectrical conditions, when the responses of target objects in the measured signal are relatively small and mixed with responses of rugged topography, 3-D inhomogeneities in overburden layers, and other interfering 3-D objects. For parameterization of the geoelectrical model of the geological medium, global and local structures are used. A block structure is a grid with large cells whose boundaries can move during the inversion process. Block structures are characterized by two types of parameters: geometric and physical. Geometric parameters include the coordinates of the boundaries of blocks in block structures, which are used for recovering local bodies or 3-D inhomogeneities within the layers, and physical parameters are the conductivities inside the blocks. In addition, the geometric parameters include displacements of control points, which are used for describing curved surfaces. The functional employed for inversion includes regularizing terms that allow controlling the self-crossing of geometric boundaries and extension of physical parameters beyond the boundaries of the allowed values range. Regularization coefficients are calculated adaptively at each iteration of the nonlinear 3-D inversion. In order to separate the responses of 3-D inhomogeneities located under the overburdens from those of 3-D inhomogeneities inside the overburdens, we propose to carry out 3-D inversion in two stages. At the first stage, over a shortened time range, we recover the conductivity distribution using global block structures and the shape of the boundaries of the overburden layers using control points. At the second stage, the entire time range is used. In those places where the significant residuals remained at late times, local block structures are employed to recover local objects (including target ones) under the overburden layers. This enables us to define quite accurately the position in plan, top border depth, and type of 3-D inhomogeneities, which are located under the overburdens, at the second stage of geometric inversion. To calculate 3-D time-domain electromagnetic fields, we use the vector finite element method implemented on optimized non-conforming hexahedral meshes with the possibility of adjoining the faces of several finite elements to the face of one finite element. The workability of the proposed approaches is demonstrated on synthetic airborne TD-EM data as well as on experimental airborne data, which are obtained as a result of methodical work over the kimberlite pipe deposit. The proposed geoelectrical model parameterization and the approach to 3-D inversion allow the discovery of relatively small 3-D target objects, when many non-target objects, including 3-D inhomogeneities in the overburdens, give several times greater responses in the measured signals.

Airborne Transient Electromagnetic Simulation: Detecting geoelectric structures for HVdc monopole operation

Geoelectric structures have great influence on the earth surface potential (ESP) induced by ground return currents (GRCs) in high-voltage dc (HVdc) monopolar operations. Traditional ground-detection methods are cumbersome due to the long distances between the grounding electrodes of substations. The airborne transient electromagnetic (ATEM) method has become a popular technique for exploring large-scale geoelectric structures. First, we analyze the influences of different 3D geoelectric models on the fluctuation in GRCs and propose a 3D model to evaluate ATEM simulations. Second, we present an efficient ATEM simulation method based on a finite-element (FE) algorithm to obtain the 3D geoelectric structure used to calculate the ESP. The stability and convergence rate of solving FE systems are improved by using an induced dimension reduction (IDR) solution algorithm. The detectability of the ATEM method is validated by an inversion case based on the Occam algorithm. The numerical results demonstrate that our robust ATEM simulation method is useful for detecting the 3D geoelectric structure used in ESP analysis.

Applicability of Transient Electromagnetic Surveys to Permafrost Imaging in Arctic West Siberia

Detection of faults and other zones of weakness in shallow permafrost to a few hundreds of meters is extremely important for ensuring the safety during the production and transportation of fuels (oil and gas). The construction of line facilities (power lines and pipelines) should be preceded by detailed surveys in order to localize major areas of potential hazard. Furthermore, reliable geophysical methods are necessary for exploration of gas hydrates. This research aims at proving that induction-based electromagnetic surveys are applicable for permafrost studies and at finding new evidence for the similarity and difference of the permafrost structure in different regions of Northern Siberia. TEM curves are collected in several regions of Northern Siberia with continuous, mostly continuous, and discontinuous permafrost. Transient electromagnetic (TEM) surveys performed in the Russian Arctic image the permafrost structure to a depth of 500 m. The data are acquired with telemetric systems that allow varying the survey design and loop configuration. Advanced processing tools are used to provide geologically essential information from late-time records, while optimized inversion algorithms are applied to obtain high-quality layered resistivity models. The resulting geoelectric models reveal evident variations in the thickness of highly resistive frozen rocks and the presence of unfrozen patches. The induction surveys, which require no galvanic contact with the earth and no grounding, are inferred to be best suitable for imaging the frozen shallow subsurface. The TEM-based resistivity patterns clearly resolve the permafrost base, as well as the contours of unfrozen zones (taliks), lenses of saline water (cryopegs), gas hydrates, and frost heaving features. The reported results can make basis for the choice of geophysical methods for permafrost studies in such harsh conditions as the Russian Arctic. Furthermore, the presented resistivity patterns can make reference for future studies of permafrost in Northern Siberia.

3D Modeling of Time-domain AEM Fields with IP Effect in Complex Media with Topography

We present two approaches to solving the airborne electromagnetic (AEM) problems given the induced polarization (IP) effect: with calculating the field in a polarizable medium directly in the time domain (TD) and with calculating the EM+IP field in the frequency domain (FD) followed by a transition to the time domain. The first approach is based on calculating the field at each time step given the sources that depend on the currents excited in the medium at previous time steps. This approach allows us to use any IP decay functions. The frequency domain approach is based on the Fourier series expansion of a non-stationary source and the Cole-Cole model. In order to reduce the computational cost, we use the Hermite spline interpolation. Both approaches allow modeling EM + IP processes in complex media with topography and the curved boundaries of layers containing 3D heterogeneities. 3D modeling is performed on non-conforming hexahedral meshes generated fully automatically. The analysis of computational efficiency and verification of the developed approaches are presented in comparison with the results from other researchers. Moreover, we compare the results obtained in the time and frequency domains. The results of 3D modeling the IP effects, which are obtained for some geoelectrical models typical for AEM exploration problems, are demonstrated.

Deep crustal resistivity structure of the Lohit Valley in the Eastern Himalayan Syntaxial region

The paper discusses the magnetotelluric derived electrical resistivity cross‐section of deep crust along the Lohit Valley in the Eastern Himalayan Syntaxial bend region. A low‐angle, north‐east dipping, intra‐crustal low resistive layer (IC‐LRL) is a dominant feature in the resistivity cross‐section. We interpret IC‐LRL as a signature of Main Himalayan Thrust. In the geoelectrical model, all the major thrusts separating different tectonic zones across the profile coincide with the dipping conducting features and these thrusts merged to IC‐LRL. The Lesser Himalaya and the Lohit Plutonic Complex are imaged as resistive features. Conductive zone between the Lesser Himalaya and Lohit Plutonic Complex reflect the Tidding Suture Zone. Conductivity of the IC‐LRL is lower in comparison with IC‐LRL imaged in another sector of the Himalaya. We suggest this difference is due to the significant difference in the intensity of the tectonic processes in this part of the Himalaya as compared to elsewhere.

The exploration of gravel layer with 3D magnetotelluric data

The Horgos area of the thrust belt on the southern margin of the Junggar Basin has a good prospect for oil and gas exploration. However, because of the complex surface conditions and the coverage of the gravel layer, the seismic data on the southern margin thrust belt have some poor imaging, which makes the three-row structural pattern unclear. It is urgent to use 3D magnetotelluric (MT) exploration to investigate the distribution of gravel layer for seismic processing to build shallow model. In this paper, a 3D geoelectric model is established using MT data and logging data collected in the study area. Through the forward modeling and inversion calculation, the feasibility of using 3D MT data to explore the high resistivity gravel layer of various thickness is verified. Phase tensor analyses indicate the shallow (> 0.1 Hz) electrical structure is mainly 1D or 2D, while the deep structure is affected by 3D structure. The 3D conjugate gradients inversion method is used to process the MT data of the study area, the forward responses of the inversion result fit the observed data well and the electrical layers of the 3D inversion is consistent with the electrical characteristic revealed by the electric logging data. All these indicate the reliability of the 3D inversion results. The 3D MT results are first used to interpret the distribution and thickness of two sets of gravel layers in the study area. It is mainly used to assist the seismic exploration to solve problems involving exploration of complex surface carbonate rocks, exploration of deep complex structures and identification of shallow lithology. It proves that 3D MT is an effective technique for the gravel and shallow lithology exploration in similar regions.

Implementing Electrical Resistivity Tomography to Delineate Soil Contamination Zone, Southern Baqubah City, Iraq

An electrical resistivity tomography survey was carried out in Diyala University campus, southern Baqubaa city, Iraq. The main aim of this study is to evaluate the efficiency of electrical resistivity tomography to detect the buried sewage system as well as to assess its environmental impact on the surrounding soil. Six parallel resistivity profiles were carried out at a perpendicular direction to the axis of the sewage system. Two-and three-dimensional geoelectrical models were constructed to determine the distribution of resistivity and its relation with both buried structures and contaminated zones. The results showed an intermediate relative resistivity zone (6-10 Ω.m) and several rounded very low resistivity zones (< 1 Ω.m), identifying the underground sewage system and contaminated soil, respectively. Based on variations in resistivity values, six holes (h1, h2, h3, h4, h5, and h6) were drilled. A total of six soil samples at 1.5m depth (1 sample per hole) were collected for heavy metals concentrations analysis. The results of the chemical analysis showed a higher concentration of heavy metals near the septic system than that the area away from it. Much lower resistivity zones (<1 Ω.m) and the higher concentration of heavy metals observed near septic system indicate the impact of contamination by migration from the septic tank into the nearby soil. The results of this study confirm the efficiency of electrical resistivity tomography for detecting a buried object and mapping contaminated zone for engineering and environmental applications.

Three-dimensional inversion of magnetotelluric sounding data in the Southern Ladoga area

The article presents the results of the interpretation of magnetotelluric soundings performed in the Southern Ladoga region. When performing the 3D inversion, both new data obtained by the LADOGA working group in 2018–2021 and data from the profile 1-EV (the “Loop” section) worked out in the early 2000s were used. Based on the results of automatic inversion performed in the ModEM program (Egbert and Albert), a three-dimensional geoelectric model of the earth’s crust to a depth of 60 km is constructed, which shows the complex heterogeneous structure of the studied territory.In the geoelectric model, two anomalous zones of core electrical conductivity of the south-eastern and north-eastern directions are distinguished, the first of which is a continuation of the well-known Ladoga anomaly. The presence of the second conducting structure confirms the results of single magnetovariational sounding performed by Igor Ivanovich Rokityansky in different parts of the East European Platform in the early 80s of the last century.

New magnetotelluric data in the suture zone of Fennoscandia and Sarmatia

Presents the results of magnetotelluric soundings acquired in 2020 along the profile Rzhev– Velikie Luki, in the suture zone of three parts of Precambrian crust of East European platform: Fennoscandia, Sarmatia and Volga–Ural. In the central part of the profile, anomaly zone of increased conductivity in the crust was revealed. The crust conductor is weakly expressed on the components of the telluric tensor due to the screening effect of the conductive sedimentary cover; therefore, the focus in the qualitative analysis of data and inversion was made on magnetovariational parameters.According to the results of two–dimensional inversion carried out in the program of A.E. Kaminsky ZONDMT2D, on the geoelectric model a subvertical zone of low resistivity in the crust is identified, which is probably associated with the paleosubduction zone of the Belarusian Ocean Plate.

Electrical anisotropy of terrigenous deposits: a brief overview of approaches to its determination from electrical logging data in vertical wells

The article briefly reviews a number of publications on the problem of determining rocks electrical resistivity anisotropy (primarily of sedimentary genesis) using downhole resistivity logs. We provide the information on the main causes of sandy-clay sediments micro- and macroanisotropy according to Russian papers and the history of the model-based approaches to the resistivity anisotropy description according to Russian and foreign articles. We analyze the main approaches to the vertical resistivity estimation. Both new hardware solutions aimed at direct measurement of electromagnetic field components sensitive to anisotropy and methodological techniques for extracting this information from the signals of "conventional" resistivity logging tools are considered according to published studies. The hardware solutions are multicomponent measurements with inclined and perpendicular (to the tool axis) coils, as well as with coaxial toroidal coils. Methodological techniques include combining data measured by tools with different types of medium excitation, for example, induction and galvanic. A number of papers suggest a two-step scheme: the first step is to determine the horizontal resistivity using induction arrays data, and the second step is to determine the vertical resistivity using focused lateral logs. Such schemes are implemented using numerical inversion algorithms and in some cases by inventing transformations of measured signals. Adding anisotropy to the interpretational model is based on a priori data (core studies, microresistivity logs). In the absence of a priori data, anisotropy is added when it is impossible to reconcile the parameters of isotropic models built independently based on logs with different type of excitation. A special focus of the review is on the development of the theory of unfocused lateral logging (BKZ) method by Soviet and Russian scientists and on the history of research on the electrical anisotropy influence on the signals of gradient probes. Due to the widespread use of the method in the USSR, this topic is presented in a number of papers revealing the results of anisotropic geoelectric models theoretical studies, numerical and physical modeling of BKZ logs and methodological developments for their interpretation.