Electromagnetic Monitoring Research Articles

Layered massive fracturing of carrier beds commercially unveils the deep tight sandstone gas reserves in Sichuan Basin

Achieving commercial production from deep tight gas formations poses challenges to existing geological and engineering technologies. Xujiahe tight sandstone gas, deeply buried in the Western Sichuan Basin, is proven with enormous reserves; however, preliminary hydraulic fracturing trials mostly failed to bring up the productivity. From the angle of incorporating geological and engineering knowhow, we first adopted the carrier beds theory to distinguish the favorable zones in Xujiahe Formation, then a dual sweet spot identification criterion was established based upon analytic hierarchy process, which links major geological and engineering parameters together. Provided the identified sweet spot, hydraulic fracture conductivity was then optimized to maximize the productivity. Fracturing operational parameters consisting of fluid volume and pumping, proppant size and addition, and fluid formula were then screened to secure high conductivity. Implementation of this updated geological-engineering technical route in exploiting Xujiahe tight gas reservoirs turns out to be a great success with an average gas rate of 130 Mm3/d/well during the early production stage in 14 wells. Electromagnetic monitoring further demonstrated the effectiveness of precise massive fracturing by visualizing the morphology of fracture clusters. Comparative productivity analyses manifested the breakthrough of this technical route over preceding ones in Xuejiahe gas reservoirs, providing a superior reference for discovering and developing deep tight gas resources around the world.

Assessment of hydrogen-induced material degradation using electromagnetic testing technology

The production, transport and use of green hydrogen are key issues for the efficient use of renewable energies. Hydrogen is able to compensate for both temporal and spatial fluctuations that naturally occur in the production and consumption of renewable energies, regardless of weather conditions, and thus can act as an efficient energy storage medium. The use of existing gas pipelines in a dynamically operated pipeline network offers particular potential for the transport of green hydrogen with regard to sustainability, resource conservation and economic efficiency. In this context, dynamic means that pressure fluctuations are permissible to a certain extent in the operation of gas pipelines. However, a hydrogen-induced degradation of the mechanical material properties can lead to brittle fracture and manifest itself in sudden material failure. Such failure must be excluded in safetyrelevant infrastructures. Hence, it would be beneficial to detect fatigued or degraded areas in the material at an early stage, especially in the context of possible increased crack growth rates associated with hydrogen embrittlement. In addition to fatigue data, which are crucial in the calculation and design of gas pipelines, non-destructive inspections are particularly important in subsequent operation to monitor the current condition of the pipelines. Non-destructive testing focuses primarily on defects such as cracks that have already developed or on visible corrosion attack. The fatigue condition, i.e., the probability of crack initiation and crack propagation is hard to evaluate. However, this can be addressed by an electromagnetic test method capable of evaluating the current state of the material. In the presented paper, an electromagnetic test method is presented, which is able to detect and evaluate hydrogen-induced material degradation. In subsequent stages, such a method can then be used as an electromagnetic monitoring system in fatigue tests, thus providing new potential for condition assessment.

Transient Electromagnetic Monitoring of Permafrost: Mathematical Modeling Based on Sumudu Integral Transform and Artificial Neural Networks

Due to the ongoing global warming on the Earth, permafrost degradation has been extensively taking place, which poses a substantial threat to civil and industrial facilities and infrastructure elements, as well as to the utilization of natural resources in the Arctic and high-latitude regions. In order to prevent the negative consequences of permafrost thawing under the foundations of constructions, various geophysical techniques for monitoring permafrost have been proposed and applied so far: temperature, electrical, seismic and many others. We propose a cross-borehole exploration system for a high localization of target objects in the cryolithozone. A novel mathematical apparatus for three-dimensional modeling of transient electromagnetic signals by the vector finite element method has been developed. The original combination of the latter, the Sumudu integral transform and artificial neural networks makes it possible to examine spatially heterogeneous objects of the cryolithozone with a high contrast of geoelectric parameters, significantly reducing computational costs. We consider numerical simulation results of the transient electromagnetic monitoring of industrial facilities located on permafrost. The formation of a talik has been shown to significantly manifest itself in the measured electromagnetic responses, which enables timely prevention of industrial disasters and environmental catastrophes.

Grounded source transient electromagnetic 3D forward modeling with the spectral-element method and its application in hydraulic fracturing monitoring

A long wire with large current source transient electromagnetic (TEM) monitoring, with a large detection depth, low cost, safety, and environmental protection, has unique advantages in the testing and identification of unconventional reservoir fluid and the evaluation of stimulated reservoir volume. So, the TEM 3D forward modeling method has become a research hotspot. Although the finite-element method (FEM) is a type of numerical algorithm that has been widely applied in three-dimensional (3D) electromagnetic field forward modeling, the efficiency and accuracy of FEM require further improvement in order to meet the demand of fast 3D inversion. By increasing the order of the basis function and adjusting the principle of mesh discretization, the precision of the mixed-order spectral-element (SEM) result will be increased. The backward Euler scheme is an unconditionally stable technique which can ignore the impact of the scale of the time step. To achieve a better description of the nonlinear electromagnetic (EM) response of the grounded source TEM method and to optimize the efficiency and accuracy/precision of the 3D TEM forward modeling method significantly, we proposed the use of 3D TEM forward modeling based on the mixed-order SEM and the backward Euler scheme, which can obtain more accurate EM results with fewer degrees of freedom. To check its accuracy and efficiency, the 1D and 3D layered models are applied to compare the SEM results with the semi-analytical and FEM solutions. In addition, we analyzed the accuracy and efficiency of the SEM method for different types of order basis functions. Finally, we calculated the long-wire source TEM response for a practical 3D earth model of a shale gas reservoir for fracturing monitoring and tested the feasibility of the TEM method in a hydraulic fracturing monitoring area to further demonstrate the flexibility of the SEM method.

ELECTROMAGNETIC MONITORING DURING THE AFTERSHOCK PERIOD OF THE 2003 CHUYA EARTHQUAKE IN THE MOUNTAIN (GORNY) ALTAI: MEASUREMENT METHODOLOGY, RESULTS

The article considers the method of observations, interpretation of data and results of electromagnetic monitoring with a controlled source for one of the seismically active regions of Siberia – Mountain (Gorny) Altai. The monitoring is carried out during the aftershock period in the epicentral zone of the destructive Chuya earthquake of 2003 with M=7.3. For regular observations, a measurement technique has been developed with several modifications of the transient electromagnetics method (TEM) to determine variations in electrical resistivity and anisotropy coefficient. The long-term series of these two geoelectric parameters of the section are presented, compared with the characteristics of the ongoing seismic events. The analysis shows that variations in electrical resistance and electrical anisotropy reflect the development and gradual attenuation of aftershock activity of a powerful earthquake. The advantages of the TEM method and the chosen methodology for monitoring in complex areas are reflected.

Elastic and electromagnetic monitoring of TRC sandwich panels in fracture under four-point bending

Textile-reinforced cementitious (TRC) sandwich panels with insulation core are mechanical- and material-efficient composites, however, under service loads might develop complex fracture that is still inadequately detected. Among damage mechanisms, the weak core-facing interfacial bond can substantially reduce its load-bearing capacity and lead to premature failure; therefore, early detection of damage is crucial to guarantee optimal long-term structural performance. Periodic inspection is necessary during the service life, however, there is neither a standardized methodology nor monitoring protocol that detects and characterizes premature interfacial debonding. In this study, a novel multi-modal monitoring is developed for the first time, based on acoustic emission (AE), digital image correlation (DIC), and millimeter wave (MMW) spectrometry, to characterize the response to bending of TRC sandwich beams. The core-facing interlaminar bond is artificially weakened during casting to simulate manufacturing defects. The proposed methodology showed high sensitivity to damage and complementarity of the techniques, where, AE allowed to characterize and locate damage, MMW showed high sensitivity to progressive failure, and DIC provided the strain data to validate and interpret AE, and MMW results.

High Temperature Magnetic Properties of Selected Steel Grades

In order to effectively control the microstructure of steel strip during manufacture it is vital that techniques be developed to monitor microstructural changes in the steel at high temperatures. Electromagnetic non-destructive testing is increasingly being used in these applications as it is non-contact, robust, relatively inexpensive and has the potential to provide real-time feedback to control the manufacturing process. However, if the data produced by these systems is to be fully exploited it is necessary to accurately measure the magnetic properties of steel grades of interest at temperatures up to the Curie point. This work details measurements carried out to assess the magnetic properties of selected steels grades, supplied by Tata Steel, up to the Curie temperature using a novel test rig based on a modified Epstein frame designed by the University of Manchester with high temperature trials at the University of Warwick. Several steel grades are studied with the full magnetic hysteresis (BH) loops reported during heating and cooling, along with extracted magnetic parameters including coercivity, magnetic saturation and magnetic permeability. The magnetic parameters of the selected steel grades are compared and implications of the results on electromagnetic monitoring of steel strip during manufacture considered. Results show the developed system has the potential to provide valuable data to inform online electromagnetic monitoring systems.

Evaluating the impact of correlated noise for time‐lapse transient electromagnetic (TEM) monitoring studies

AbstractTypically, transient electromagnetic (TEM) hydrogeological applications focus on spatial characterization. However, there is scope for utilizing time‐lapse TEM to monitor dynamic processes. Changes related to hydrogeological processes are subtle; consequently, measurements must be of exceptional quality, and the presence and influence of noise sources must be well understood. A potentially problematic noise source is radio waves operating in the 3–300 kHz range, as they introduce correlated error into TEM measurements. For instance, it was anticipated that such radio waves could introduce smooth perturbations in the data that could be erroneously interpreted in the TEM inversion results. This work evaluates the presence of correlated noise sources, their temporal dependence and their significance for TEM monitoring. This work combines fully sampled data and normalized covariance matrices of gated data to identify correlated noise sources. Radio signals operating in the low and very low frequency (LF and VLF) bands were found to vary across the investigation period; however, their influence on the TEM inversion results was minimal. Measurement stacking remains an effective way to improve the signal‐to‐noise ratio of TEM data affected by LF and VLF noise sources as they do not introduce bias, for example smooth perturbation, into the TEM data explored in this work.

Electromagnetic Monitoring of Modern Geodynamic Processes: An Approach for Micro-Inhomogeneous Rock through Effective Parameters

This study focuses on microscale anisotropy in rock structure and texture, exploring its influence on the macro anisotropic electromagnetic parameters of the geological media, specifically electric conductivity (σ), relative permittivity (ε), and magnetic permeability (μ). The novelty of this research lies in the advancement of geophysical monitoring methods for calculating cross properties through the estimation of effective parameters—a kind of integral macroscopic characteristic of media mostly used for composite materials with inclusions. To achieve this, we approximate real geological media with layered bianisotropic media, employing the effective media approximation (EMA) averaging technique to simplify the retrieval of the effective electromagnetic parameters (e.g., apparent resistivity–inversely proportional to electrical conductivity). Additionally, we investigate the correlation between effective electromagnetic parameters and geodynamic processes, which is supported by the experimental data obtained during monitoring studies in the Tien Shan region. The observed decrease and increase in apparent electrical resistivity values of ρk over time in orthogonal azimuths leads to further ρk deviations of up to 80%. We demonstrate that transitioning to another coordinate system is equivalent to considering gradient anisotropic media. Building upon the developed method, we derive the effective electric conductivity tensor for gradient anisotropic media by modeling the process of fracturing in a rock mass. Research findings validate the concept that continuous electromagnetic monitoring can aid in identifying natural geodynamic disasters based on variations in integral macroscopic parameters such as electrical conductivity. The geodynamic processes are closely related to seismicity and stress regimes with provided constraints. Therefore, disasters such as earthquakes are damaging and seismically hazardous.

Bayesian optimization based random forest and extreme gradient boosting for the pavement density prediction in GPR detection

The Ground penetrating radar (GPR) adopts non-destructive and continuous electromagnetic (EM) monitoring technology that is influenced by the dielectric properties of transmission mediums and is of interest in the density detection of asphalt pavement. Prediction of in-place density based on the dielectric properties of pavement materials is a crucial aspect of GPR density detection. This study introduced the random forest (RF) and extreme gradient boosting (XGBoost) approaches that combine the state-of-the-art Bayesian hyper-parameter optimization (BHPO) and 5-fold cross-validation for density prediction. The pavement density data collected from the literature, laboratory, and field tests in the G42S expressway are used for training, testing and validating the models. The input to the RF and XGBoost models was the data for seven material parameters, and the output was the corresponding asphalt mixture or pavement density. The results indicated that BHPO significantly increased the accuracy of density prediction and captured the optimal combination of hyper-parameters for RF and XGBoost models. The XGBoost and RF models were well defined after BHPO and the XGBoost outperformed the RF and other theoretical models. In the validation set, machine learning (ML) algorithm-based density models reduced pavement density prediction error from 3% to about 0.3%. Features importance analysis illustrated that the ratio and density of asphalt to aggregate is the decisive factor for pavement density. The critical factor affecting the density monitoring is the accuracy of the dielectric constant detection using the GPR. The present study implied that the ML algorithms could significantly improve the accuracy of the GPR system. The coming decade promises considerable advances in combining the GPR system and ML.

Electromagnetic monitoring with local mesh for time-lapse monitoring of hydraulic fracturing

The controlled-source electromagnetic method (CSEM) is a useful tool for monitoring underground fluid movement due to hydraulic fracturing. To understand the characteristics of time-lapse monitoring, an efficient three dimensional(3D) forward modeling is a premise. However, 3D finite element method (FEM) employs the normal mesh that applies fine grids to model the whole sensitive area, resulting in a large degree of freedom (DOF) of the equation that is associated with expensive computation cost. Moreover, time-lapse monitoring requires continual expensive calculations, which lead even an unacceptable computational burden. Inspired by the fact that during the hydraulic fracturing, the resistivity changes occur in a limited domain, we propose a method called as the FEM with local mesh, which is based on secondary field equation to model the EM field perturbation due to hydraulic fracture, and uses fine grids on the fracturing area with resistivity change and as large grids as possible to represent other areas without resistivity change. Therefore, the DOF can be reduced significantly. The numerical tests demonstrate that our method is accurate and has only 10% of the DOF of conventional method.

Advances in Marine Intelligent Electromagnetic Detection System, Technology, and Applications: A Review

This paper introduces the current state of the art in marine intelligent electromagnetic detection sensors, systems and platforms for the detection and health monitoring of offshore structures, especially for subsea cables and pipelines. The presented survey is by no means exhaustive, but introduce some notable results and relevant techniques in the detection and inspection of marine structure electromagnetic monitoring fields. Particularly, this paper presents a review of the main research works focusing on electromagnetic detection techniques and intelligent marine vehicles for subsea cables. The marine electromagnetic exploration techniques are elaborated as active and passive detections based on different electromagnetic field generation and sensing principles. The pulse induction-based detection method for subsea ferromagnetic lines detection, transient and controlled-source electromagnetic systems in marine geological fields under the category of active detection approach, are reviewed. According to the classical applications on subsea cable-like target inspection, the passive detection approach is detailed classified as crisscrossing detection and along-tracking detection, which are characterised by different trajectories of detection vehicles. Finally, the paper discusses the marine electromagnetic detection techniques in general and highlights challenges that need to be addressed in developing detection vehicles with lower electromagnetic noises and advanced autonomy on carrying out detection missions.

An electromagnetic monitoring method based on underground charging conductor for hydraulic fracture diagnostics

Hydraulic fracturing is a key technology for oil and gas production and energy conversion. To ensure the ideal fracturing operation, real-time monitoring is required. This paper proposes an electromagnetic monitoring method based on underground charging conductor. By this method, electromagnetic waves are directly excited at the fracture initiation site by supplying power to the wellbore, and the electric field changes caused by hydraulic fracturing are observed on the ground. Using the single fracture model, we derive the potential formula of the charging conductor on the ground. Water tank experiments show that this method can measure the potential anomalies before and after the fractures are formed and can show the fracture orientation. We apply this technology to the fracturing monitoring for the hot dry rock in well GR1 and obtain high-precision electromagnetic signals in real time. By the charging conductor model, we calculate the fracture orientation and length, as well as the fracturing fluid diffusion range. We also analyze the influence of different fracturing technologies on fracture development and complexity. This study provides reference for adjusting fracturing parameters, optimizing fracturing scheme and deploying heat exchange wells.

EMD based statistical analysis of nighttime pre-earthquake ULF electric field disturbances observed by CSES

To explore the correlation between earthquakes and spatial ultra-low frequency electric field disturbances and to study the phenomenon of seismic ionospheric disturbances, this study uses 3 years of electric field ULF band data from 2019 to 2021 observed by the electric field detector carried by the CSES to identify anomalous disturbances using the anomaly automatic detection algorithm based on empirical mode decomposition for the 2,329 seismic events of magnitude not less than 5.0 and the electric field ULF disturbances in this period are analyzed by Superposed Epoch Analysis, and the statistical results are compared and analyzed in depth by earthquake location and different magnitudes in terms of both spatial and temporal scales and spatial distribution. The results show that: 1) There is a correlation between earthquakes of magnitude not less than 5.0 and ultra-low frequency disturbances in the electric field. The abnormal disturbance mainly occurred 11 days before the earthquake, 2 days before the earthquake to the day of the earthquake, and the location of the earthquake is within 200 km from the epicenter. 2) Sea earthquakes can observe more pre-seismic anomalous electromagnetic disturbances than land earthquakes. 3) In terms of earthquake magnitude, the larger the magnitude, the earlier the pre-earthquake anomalous disturbances appear and the wider the range of anomalies. This study provides an effective way to explain seismic ionospheric phenomena, and also provides a reference for the application of electromagnetic monitoring satellites in earthquake prediction and early warning as well as disaster prevention and mitigation.

The joint seismic-and-electromagnetic monitoring with electromagnetic field separation

The magnetotelluric soundings (MTS) are a common tool in applied geophysics. The guidelines for electromagnetic (EM) monitoring should be updated because of new tools and software developed. Some techniques paragraphs have outdated sections. Some essential equipment requirements and its’ allowable parameters, MTS acquisition, are defined. We involve Research Station RAS patents (RU 175972 U1, 2017; RU 2701876 C1, 2018) to increase the long-term stability of electrical parameters of non-polarizable electrodes. We consider the irreversible rock deformations form sources of the electromagnetic field of endogenous origin as geodynamic processes. We offer MTS with an additional algorithm with electromagnetic field separation for studying the endogenous component of EM field as a lower half-space impedance. We explain the technology of MTS in seismically active zones with remote access on the example of the Tien Shan. We introduce these guidelines acquiring data system for the joint seismic-and-electromagnetic monitoring for the modern geodynamic processes. We show a result diagram for the energy characteristic of the endogenous component of EM field.

Preliminary results of clay soils state monitoring using transient electromagnetic sounding apparatus

The background for creating an electromagnetic soil sounding apparatus with receiving and transmitting antennas separated by a distance of up to 100 meters is considered in this paper. The temperature and frequency dependences of the complex dielectric permittivity of multilayer clay soil are studied in conjunction with the results of numerical simulation of ultra-wideband log-periodic antennas immersed in the soil to a depth of 1.5 m. The choice of a high-voltage generator and pulse receiver is studied, and a structure of apparatus prototype is given. Based on the results of oscillograms’ and signal spectra measurements with 30 m antennas separation, and with reference to the soil temperature, estimates of the possible limits of change in the electrophysical parameters of the clay soil at a geophysical site are provided. Conclusions are drawn about ways to improve the apparatus in order to create a new technology for transient electromagnetic monitoring of permafrost.

Mathematical Modeling of Transient Electromagnetic Sounding Signals for Monitoring the State of Permafrost

Abstract —The study is aimed at theoretical development and scientific substantiation of a high-resolution transient electromagnetic (TEM) geophysical technique for monitoring the state of permafrost. The electromagnetic monitoring configuration includes spatially distributed sounding systems for surface and borehole locations of the field sources and receivers. Changes in the electrophysical properties of the earth can be traced for the cases of both ground thawing and freezing. We developed the theory of TEM signals modeling, upon which created an algorithm for rapid and accurate numerical simulation of the electromagnetic field. The signals are scrutinized from the various sounding systems in the basic earth models as function of registration time. We show how the features associated with a spatial arrangement of frozen rocks appear on the EMF diagrams. It follows that a set of the measured data enables visual detection of the boundary between frozen and thawed rocks.

Research on Distributed Multisensor Spectrum Semantic Sensing and Recognition in Internet of Things Environment

The development of 5G technology has brought about a new era of Internet of Thing (IoT), and at the same time, electromagnetic spectrum monitoring and sensing have also ushered in huge challenges. Digital modulation recognition technology is an important content of electromagnetic spectrum sensing. In the increasingly complex wireless communication transmission environment, especially in noncooperative communication, it becomes more and more difficult to receive target signals and accurately extract effective semantic information from diverse modulation signals of the electromagnetic spectrum. At this stage, with the rapid development of network information and wireless communication technology, within a prescribed distance, the IoT built by many sensors has attracted wide attention from people in related fields. This paper proposes a distributed collaborative sensing spectrum semantic recognition architecture for communication signals based on feature fusion. Perform wireless communication and transmission between multiple sensors to form a self-organizing network to cooperatively sense signal semantic information, and extract the signal features of each sensor in the distributed network structure. Finally, the extracted sensor features are semantically analyzed and modeled, and the effective features are fused to complete the entire perception and recognition process. Even if the channel environment of a small number of receiving nodes deteriorates in a complex transmission environment, the signal quality features can still be accurately extracted, the classification and recognition effect like or higher than the best channel state performance can be achieved, and the fault tolerance of the system can be effectively improved. It can also enhance the performance of spectral semantic information sensing and recognition in the IoT environment.

Screening, Monitoring, and Remediation of Legacy Wells to Improve Reservoir Integrity for Large-Scale CO2 Storage—An Example From the Smeaheia Structure in the Northern North Sea

Carbon capture and storage (CCS) is an inevitable action to achieve CO2 emission reduction targets including becoming net-zero by 2050. Increased efforts are therefore required to identify suitable locations for large-scale CO2 storage. In addition to large aquifers, shut down oil and gas fields in the North Sea are logical candidates for offshore large-scale CO2 storage because of their proven storage capacity, reliable caprock integrity, established infrastructure, and public acceptance. However, in some cases, old and legacy wells are subject to high uncertainties in their integrity, and they can compromise CO2 containment in such reservoirs. On the Norwegian Continental Shelf (NCS), such wells are numerous even outside of oil and gas production areas, i.e., legacy wells affecting aquifers. Therefore, there is a clear need for reliable and cost-effective technologies for well integrity evaluation and remediation. This paper discusses a workflow for screening, monitoring, and remediation of legacy wells. In a first stage, the screening of the Horda Platform areas suggested the need for integrity investigation for the exploration well 32/4-1 T2, drilled into the Alpha structure of the Smeaheia fault block if CO2 is stored in the structure. Our initial well screening of drilling documentation indicates that the well is not suitable to be reused for CO2 injection and geophysical monitoring is recommended. In a second stage, a numerical representation of the well architecture is built including realistic geological setting. We evaluate the sensitivity of non-invasive low-frequency electromagnetic monitoring to corrosion levels in the casing. Numerical end-member simulations of assuming casing corrosion of different degrees by changing material conductivity are performed. Results comparing different corrosion scenarios with a base case (no corrosion) give an above noise signal at receiver locations enabling to separate the different cases. Comparison of the gained electrical fields at seafloor suggests that well casing corrosion monitoring should be possible. Finally, the electrochemical deposition potential of the Sognefjord Formation water is analyzed, revealing depositional potential for portlandite, which might be useful for cement remediation. We recommend such an analysis for all legacy wells penetrating candidate reservoirs for future CO2 or hydrogen storage.

Experimental Research of Compound Monitoring on Multiple Temporary Blocking Refracturing for Long-Section Horizontal Wells

As an important energy replacement block in China, the tight conglomerate oilfields in the Mahu area are difficult to develop and are characterized by strong heterogeneity, large horizontal stress differences, and undeveloped natural fractures. However, new development processes including temporary blocking diversion and large section-multiple clusters have been implemented on the oilfields in the past few years. In 2020, two adjacent horizontal wells in the MD well area experienced a poor fracturing development effect compared with the earlier wells in this area. Analysis suggests that the main reasons are water sensitivity of the reservoir, insufficient fracturing scale, and/or interference from the adjacent old wells. To ameliorate the problem, this study presents an experimental study of multiple temporary plugging and refracturing technology in long horizontal well sections, in combination with electromagnetic and microseismic monitoring. Results from the study show a great difference between the two monitoring techniques, which is attributed to their different detection principles. Interestingly, the combination of the two approaches provides a greater performance than either approach alone. As the fracturing fluid flow diversion is based on temporary plugging diversion and electromagnetic monitoring of fracturing fluid is advantageous in temporary plugging diversion monitoring, both approaches require further research and development to address complex situations such as multiple temporary plugging and refracturing in long intervals of adjacent older wells.