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Project titlePulsed electromagnetic sounding of permafrost: theoretical and experimental development of a high-resolution geophysical method, scientific substantiation and creation of an innovative technology for monitoring of the cryolithozone

AffiliationTrofimuk Institute of Petroleum Geology and Geophysics of Siberian Branch Russian Academy of Sciences,

Research area 07 - EARTH SCIENCES, 07-406 - Electromagnetic field, electric conductivity

KeywordsContemporary geoelectrodynamics, pulsed electromagnetic sounding, geophysical monitoring, direct and inverse problems, modeling and inversion, laboratory and field experiments, electrophysical parameters, conductive dispersive media, permafrost, cryolithozone

Annotation
The project is aimed at a comprehensive theoretical and experimental substantiation of a high-resolution method of electromagnetic sounding with a controlled current pulse for geophysical monitoring of the state of the cryolithozone. It bases on the development of geoelectrodynamics of electrically conductive dispersive media, the use of contemporary methods in computational mathematics and mathematical geophysics, the involvement of machine learning and big data processing methods, the employment of high-performance graphical and tensor accelerators, performing large-scale numerical modeling for a wide range of surface and borehole observation systems with the estimation of their capabilities and limitations, as well as conducting laboratory studies of the electrophysical properties of samples and unique field experiments on the frequency-selective propagation of electromagnetic waves in frozen rocks. The topic of the project is predetermined by the high-priority government-wide requests for the prompt creation and implementation of a state system for monitoring permafrost, in order to prevent the consequences of its degradation as well as man-made and environmental disasters, which necessitates the development of a new geophysical method and a high-tech technology of pulsed electromagnetic monitoring of the cryolithozone. The theoretical substantiation is associated with the development of numerical methods for solving electrodynamics problems in complex geological and technological conditions of the cryolithozone. The creation of a theoretical-methodological and software-algorithmic base for electromagnetic sounding of the geoenvironment requires the involvement of a mathematical apparatus that accounts for a complex geometric structure of the objects and various effects of interaction and propagation of an electromagnetic field in permafrost. Recently, for modeling electromagnetic fields, the vector finite element method has proven itself, which allows the most accurate account of conservation laws, as well as the Sumudu transform with its unique properties, which has not received a widespread use in solving geoelectrodynamics problems. Since the solutions to 3D problems of modeling electromagnetic processes require sufficiently large computational resources, it is urgent to build rapid algorithms for solving direct and inverse problems, based on the application of machine learning methods, along with high-performance graphics and tensor accelerators. An important aspect to substantiating an electromagnetic monitoring system is a comprehensive comparative and contrastive analysis of the results of large-scale numerical modeling of electromagnetic signals and spatial resolution characteristics in order to design observation systems and specify their capabilities and limitations in realistic geocryological conditions. As applied to pulsed electromagnetic sounding, it is important to determine the optimal parameters of the pulse generated by the source, which necessitates the consideration of pulses with different spectral compositions. The electromagnetic monitoring system assumes a spatially distributed configuration of various sounding systems with both surface and borehole placing of the power source. 3D numerical modeling of electromagnetic fields is performed in realistic geoelectric models of geocryological media, obtained following the results of field geophysical studies at real reference objects. Experimental validation is associated with laboratory studies of the electrophysical properties of dispersive media samples, together with field experiments. The processes of permafrost thawing or freezing are accompanied by a change in its electrophysical properties, which makes it possible to utilize electrical and electromagnetic methods for monitoring. In the latter case, the effect of frequency dispersion plays a significant role, which is associated with the existence of various relaxation processes occurring in rocks. One of the key aspects is to conduct unique field experiments on the frequency-selective propagation of electromagnetic waves in frozen rocks via the experimental pulsed electromagnetic monitoring system under development. Therefore, it seems important to carry out field experiments accompanied by laboratory analyzes. The novelty of the scientific research is primarily determined by the following factors. Firstly, in relation to electromagnetic monitoring of the state of the cryolithozone, the problem of electromagnetic sounding with a controlled pulse of a given spectral characteristic is formulated for the first time.Secondly, the scientific novelty of the numerical solutions to 3D electrodynamics problems considered in the project consists in the use of the vector finite element method in an original combination with the Sumudu transform. Thirdly, for high-performance numerical solutions to direct and inverse 3D geoelectrodynamics problems in complete mathematical formulations, we are the first to propose contemporary machine learning technologies – artificial neural networks. Fourthly, numerical modeling of electromagnetic fields is carried out in realistic geoelectric models of geocryological environments, built on the basis of the results of geophysical studies on real objects that are taken as reference ones. And, fifthly, for the first time we formulate the problem of establishing the frequency-selective propagation of electromagnetic waves, which advances the ideas of super-resolution of geophysical methods through new field experiments on a specially created geophysical test site. The new scientific ideas implemented in the project, complete formulations of electrodynamics problems, realistic models of geocryological environments, original computational algorithms and their software implementation that provide solutions to specific practical tasks of geophysical monitoring in real time do not exist. The implementation of the project and its scientific results ensure the acquisition of new fundamental knowledge and form the basis for the development of a high-resolution geophysical method and the creation of an innovative technology for monitoring the state of the cryolithozone.

Expected results
The scientific results of the project are aimed at solving the fundamental problem of the propagation and interaction of electromagnetic waves in permafrost, which are excited by controlled current pulses of different spectral composition, with establishing their relationship with the electrophysical parameters of the electrically conductive dispersive media. The results are associated with the theoretical and experimental development of a high-resolution geophysical method, scientific substantiation and the creation of an innovative technology for pulsed electromagnetic monitoring of the state of the cryolithozone. A theoretical-methodological and software-algorithmic base of electromagnetic sounding with a controlled current pulse of a given spectral characteristic will be created by numerically solving the 3D direct and inverse problems in complete mathematical formulations through the vector finite element method with high-order basis functions, with an original combination of the Sumudu transform, machine learning methods, and big data processing using high-performance graphics and tensor accelerators. The developed computational schemes and software-implemented algorithms for resource-intensive numerical solutions of the 3D electrodynamics problems will be characterized by high computational performance. The use of neural network technologies and the Sumudu transform will provide real-time modeling and data processing with low requirements for computing devices applied for geophysical investigations directly in the field. There will be carried out large-scale numerical modeling of electromagnetic sounding signals with controlled current pulses of different characteristics, based on sounding systems with various spatially distributed surface and borehole configurations, with the establishment of their spatial resolution, capabilities and limitations. The numerical modeling will comprise 3D geoelectric models of electrically conductive dispersive media, obtained during field and laboratory research. An important aspect is creating realistic geoelectric models of geocryological environments, acquired on the basis of the numerical inversion of field electrotomographic surveys and laboratory studies on the temperature-frequency-dependent electrophysical properties of the samples through multifrequency dielectric measurements with regard to reference engineering-geological objects. Unique field experiments will be carried out on the frequency-selective propagation of electromagnetic waves in the near-surface strata during the seasons of its aggradation and degradation, using the developed prototype of a pulsed electromagnetic monitoring system at a specially created geophysical test site (Novosibirsk Region, Dorogino settlement). One of the key aspects is testing the technology for pulsed electromagnetic monitoring of the state of the cryolithozone and the equipment under development at selected reference objects (Republic of Sakha (Yakutia) and others). It will be accompanied by a geological and geophysical interpretation of the recorded signals, which predetermines the extremely high practical significance of the scientific results. The comprehensive and large-scale research will ultimately prove the unique capabilities of the electromagnetic sounding with controlled current pulses to effectively monitor the state of the cryolithozone. The scientific and practical significance of the results follows from the achievement of a new level of scientific substantiation for the innovative technology. All of it bases on fundamental results obtained by contemporary methods in computational geophysics and machine learning, performing large-scale 3D numerical modeling in realistic geoelectric models, and is confirmed by the results of laboratory research and field experiments to ensure a high efficiency of the pulsed electromagnetic monitoring of the state of permafrost. The expected scientific results are new and correspond to the world level of research.

Annotation of the results obtained in 2022
1. A theoretical-algorithmic base for transient electromagnetic sounding of permafrost was developed. We developed and implemented in software a computational scheme for three-dimensional numerical simulation of transient electromagnetic sounding through the vector finite element method and Sumudu transform for realistic geoelectric models of permafrost. Discretization with respect to spatial variables was carried out using high-order basis functions on a tetrahedral grid. The problem was reduced to solving a set of independent systems of high-dimensional linear equations. The computational scheme is parallelized to speed up calculations. Based on numerical solution to the first-kind Fredholm equation via the collocation method, we created an algorithm for performing the inverse Sumudu transform, which is resistant to noise in the input data. In order to solve an ill-conditioned integral equation, a regularization procedure with automatic choice of parameters was constructed. To train artificial neural networks by the developed computational modeling algorithm, data sets were generated, consisting of functions and their Sumudu images. The data set is formed both from functions that have analytical images and from those obtained after the numerical inverse Sumudu transform of the images. The augmentation procedure was applied to the data set to expand the training set. The neural network was trained by the adaptive moment estimation algorithm with parallel computing on high-performance graphics accelerators. We elaborated a computational algorithm for solving the direct problem by means of the inverse Sumudu transform combined with neural network technologies. We tested the transient electromagnetic sounding computational algorithms, made estimates of their speed and performance. Also, we undertook a comparative and contrastive analysis of the results and numerical simulation methods. The relative error in calculating the electromotive force does not exceed 0.1% in comparison with exact analytical solutions. The inverse Sumudu transform algorithm based on artificial neural networks provides an increase in performance by more than two orders of magnitude, with less resource consumption. 2. Large-scale simulation of transient electromagnetic sounding signals in realistic earth models was carried out. Internal parameters of the computational algorithms for three-dimensional numerical simulation were tuned, taking into account the geoelectric features characteristic of the geophysical polygon section. The geometric features of media were considered when constructing a computational tetrahedral grid. Their dispersive properties are reflected in the mathematical model when discretized in time. We performed a comparative analysis with the numerical simulation results in the class of layered-homogeneous geoelectric models of electrically conductive dispersive media. The relative error in calculating the electromotive force does not exceed 0.2% in comparison with verified numerical-analytical solutions. Realistic geoelectrical models for the near-surface part of the geophysical test site (Novosibirsk Region, Dorogino settlement) were created, following the results of two-dimensional numerical inversion of resistivity tomography data with different observation systems and laboratory studies of frequency-dependent electrical parameters of sandy-clayey samples. The section of the polygon in the depth range up to 50 m is represented by three layers with contrasting resistivities. There were numerical three-dimensional simulation and analysis of transient electromagnetic sounding signals in geoelectric models of electrically conductive dispersive media, including realistic models of the geophysical test site with electrical parameters established from the results of field observations and laboratory studies of the soil samples. An analysis was conducted for electromagnetic sounding signals with different characteristics of current pulses, which involved various configurations of surface/borehole sounding systems as well as their sensitivity functions, with an assessment of the spatial resolution characteristics stemming from the large-scale numerical simulation results. We identified distances between the sources and receivers, field components, and pulse shapes for reliable localization of the thawed/frozen layer boundary. 3. A series of laboratory and natural experiments was run. Field resistivity surveys were carried out by applying the resistivity tomography method at the geophysical test site by a multi-electrode electrical survey station with different distances between electrodes on four test site profiles. The geoelectrical structure of the near-surface strata with different spatial resolution was established subsequent to the results of two-dimensional numerical inversion of different-depth measurements. Full-scale experiments were run with a prototype of the transient electromagnetic sounding system being developed at the geophysical test site and sand-clay quarry. The methodology for conducting the experiment was worked through, with testing the technical solutions and operability of the developed equipment in the field. We analyzed the spectral and amplitude-phase characteristics of electromagnetic signals recorded at the geophysical test site with the prototype of a transient electromagnetic monitoring system. Measurements of the amplitude-phase characteristics on the prototype in the near-surface layer are highly accurate and repeatable. A geological and geophysical interpretation of the measurements was carried out involving the results of the field resistivity surveys and laboratory experiments. The signal amplitude was shown to be characterized by the highest correlation with the soil temperature. Samples were taken of the deposits at the sandy-clayey quarry and geophysical site. We run a laboratory study of their granulometric and lithological composition, as well as of electrophysical properties in a wide frequency range, for a realistic description of geoelectric models and numerical simulation. Dielectric measurements on soil samples from the test site are in good agreement with the results of resistivity tomography. The quarry and test site are dominated by loose sedimentary rocks with a predominant content of particles of the size of dust and sand, and a significant amount of clay particles. Based on the results of the research in 2022, 4 articles have been published and accepted for publication in the leading scientific periodicals included in the WoS, Scopus and RSCI citation databases, and 2 more than articles are currently under review. The results have been approved by the scientific community. Internet link to information resources dedicated to the project: http://www.ipgg.sbras.ru/ru/science/projects/22-17-00181-impulsnoe-elektromagnitnoe-zondirovanie-mnogoletnemerzlyh-porod-2022

Publications

1. Bukhtiyarov D.A., Glinskikh V.N. Предварительные результаты мониторинга состояния глинистых грунтов при помощи установки импульсного электромагнитного зондирования Геофизические технологии, - (year - 2022)

2. Epov M.I., Nechaev O.V., Glinskikh V.N. Интегральное преобразование Сумуду для моделирования электромагнитного зондирования земных недр Russian Geology and Geophysics, - (year - 2023)

3. Nikitenko M.N. Преобразования сигналов импульсных электромагнитных зондирований в частотную область для быстрой инверсии данных Геофизические технологии, - (year - 2022) https://doi.org/10.18303/2619–1563–2022–2–15

4. Nikitenko M.N., Glinskikh V.N., Mikhaylov I.V., Fedoseev A.A. Mathematical modeling of transient electromagnetic sounding signals for monitoring the state of permafrost Russian Geology and Geophysics, No. 12, p. 1-7 (year - 2022) https://doi.org/10.2113/RGG20224514

5. - Инновации – в практику: большое интервью директора ИНГГ СО РАН по вопросам импортозамещения Пресс-служба Института нефтегазовой геологии и геофизики им. А.А. Трофимука СО РАН, - (year - )

Annotation of the results obtained in 2023
1. A theoretical-algorithmic base for transient electromagnetic sounding of permafrost was developed. To study and monitor the state of the cryolithozone, we developed a method for transforming transient electromagnetic sounding data into apparent electrical resistivity. The method is based on selecting the resistivity of a homogeneous conducting half-space. An algorithm for numerical inversion of transient electromagnetic sounding data was elaborated as a problem of minimizing the discrepancy between the Sumudu images of measured signals and the Sumudu images of calculated signals. For rapid numerical inversion, a fast analogue of a finite element algorithm was created based on an artificial neural network with a multilayer perceptron architecture. Input and output data for the artificial neural network were created. As an alternative to minimizing the functional discrepancy between the Sumudu images of measured signals and the Sumudu images of calculated signals, an operator was constructed that directly maps the measurement vector to the vector of model parameters. Artificial neural networks were also applied to approximate such an operator. Using the existing two methods for solving the inverse problem, a third one was constructed as a combination of them. Comprehensive testing of algorithms for transformation and inversion of transient electromagnetic sounding data was carried out. It was found that the neural network algorithm is 5.5 orders of magnitude faster than the finite element algorithm. Using the developed algorithms, the geometric dimensions of a talik in a characteristic geoelectric model of permafrost rocks were determined with an accuracy of 5 to 20% at different noise levels in pseudo-experimental data and depending on the distance of the talik from the sounding system. 2. Large-scale simulation of transient electromagnetic sounding signals in realistic earth models was carried out. Based on the analysis of specialized geological and geophysical publications in the field of studying and monitoring permafrost in a number of regions of Russia (Yakutia, Yamalo-Nenets Autonomous Okrug), typical geoelectric parameters of permafrost on and in which civil and industrial facilities, buildings and structures exposed to the processes of thawing and freezing of permafrost are located. Realistic geoelectric models of varying degrees of complexity were created, including structural elements of buildings and structures, zones of thawing and talik formation, taking into account polarization parameters in frozen rocks. The models include: a railway in Yakutia, an underground gas pipeline on the Gydan Peninsula, a gas field production well on the Yamal Peninsula, a five-story residential building on stilts in the city of Salekhard. Large-scale numerical three-dimensional modeling and analysis of electromagnetic sounding signals with controlled current pulses (rectangular and sign-variable) for borehole and surface-borehole systems was carried out: at different locations of observation systems relative to the talik, with a consistent assessment of the influence of geoelectric parameters of the model and talik on the measured signals in two models: railway in Yakutia and underground gas pipeline on the Gydan Peninsula. From a comprehensive analysis of the simulated signals it follows that transient electromagnetic monitoring is possible in both cross-borehole and surface-borehole versions, using both rectangular and sign-variable pulses. A talik of small size, with a low resistivity contrast, is poorly visible on pulse monitoring diagrams. In addition, variations in the electrical resistivity of loams and clay loams at a geophysical test site in the winter-spring period were calculated based on field temperature measurements in the range from –18 to +4°C, taking into account laboratory studies of core samples. We simulated transient electromagnetic monitoring of the boundary between frozen and thawed rocks during the winter-spring period in reliance on changes in the calculated electromotive force values. The components of the electromagnetic field that are most sensitive to the freezing and thawing of permafrost were selected. 3. A series of laboratory and natural experiments was run. The tasks of developing the geophysical test site and the prototype of a transient monitoring system were determined subsequent to the results of previous field tests. The measuring site was modified with the creation of new test pits to accommodate a prototype of the equipment and, in perspective, an artificial barrier in the path of the high-voltage pulse. The operating conditions of the pits were optimized for winter. Changes were made to the connection scheme of the measuring system. Full-scale experiments on the passage of the high-voltage pulse through the ground at a distance of 100 m between the transmitting and receiving antennas were successfully carried out. We established the dependence of the signal (and its spectrum) on the ground temperature to be clearly visible on the oscillogram of the signal at the output of the receiving antenna: in warmer ground the signal amplitude is 3.2 times greater than in winter, which is consistent with theoretical calculations. The prototype of the measuring system was finalized. A plan was created to further optimize the measurements and conduct new experiments. The petrophysical and electrical properties of frozen soils from a natural test site in the Republic of Sakha (Yakutia) were studied. An analysis of the lithological composition of the soils was carried out. The main lithological intervals of sediments in the well section were identified following the results of core material analysis. The granulometric composition of soils was studied using a laser particle size analyzer. Histograms of the distribution of particle sizes by volume for different depths were constructed. A laboratory study of the temperature effect on the electrical properties of the samples was carried out by means of a two-electrode method with alternating current in the range from +10°С to –7°С. The resistivity of the samples was found to be increasing when moving from the upper to the lower interval. We performed a comparative analysis of the results of numerical, laboratory and field experiments. Firstly, the values of electrical parameters obtained from the results of field geophysical studies and laboratory core analyzes are consistent with each other. Secondly, the temperature dependences of the resistivity of core samples and the resistivity obtained from the field experiments performed in the winter-spring period at the geophysical test site are comparable to each other. Thirdly, the results of both field experiments and laboratory measurements of soil properties were taken into account when constructing geoelectric models for numerical calculations, which ensures their realism. The reliability of the results of numerical calculations within the project is achieved by the simultaneous use of the most modern mathematical apparatus developed, data from field geophysical measurements, as well as laboratory measurements of core material. Based on the research results in 2022, 5 articles were published and accepted for publication in leading scientific periodicals included in the WoS, Scopus and RSCI citation databases, and 1 more article is currently being review. The results received approval from the scientific community at major conferences. Internet link to information resources dedicated to the project: http://www.ipgg.sbras.ru/ru/science/projects/22-17-00181-impulsnoe-elektromagnitnoe-zondirovanie-mnogoletnemerzlyh-porod-2022

Publications

1. Epov M.I., Danilovskiy K.N., Nechaev O.V., Mikhaylov I.V. Artificial neural network-based computational algorithm of inverse Sumudu transform applied to surface transient electromagnetic sounding method Russian Geology and Geophysics, v. 64, p. 1-7 (year - 2023) https://doi.org/10.2113/RGG20234607

2. Glinskikh V.N., Fedoseev A.A., Nikitenko M.N., Mikhaylov I.V., Bukhtiyarov D.A. Проектирование полевых экспериментов для обоснования технологии мониторинга мерзлых пород Криосфера Земли, т. 27, № 4, с. 45-53 (year - 2023) https://doi.org/10.15372/KZ20230405

3. Mikhaylov I.V., Nechaev O.V., Glinskikh V.N., Nikitenko M.N., Fedoseev A.A. Численное моделирование сигналов импульсного электромагнитного межскважинного мониторинга многолетнемерзлых пород под основаниями промышленных объектов Геофизические исследования, т. 24, № 3, с. 87-102 (year - 2023) https://doi.org/10.21455/gr2023.3-5

4. Nechaev O.V., Danilovskiy K.N., Mikhaylov I.V. Моделирование и инверсия сигналов импульсных электромагнитных зондирований в задаче мониторинга многолетнемерзлых пород с применением методов глубокого обучения Геология и геофизика, - (year - 2024) https://doi.org/10.15372/GiG2023211

5. Nikitenko M.N., Bredikhin I.A., Mikhaylov I.V., Fedoseev A.A. Трансформация данных импульсных зондирований в кажущиеся электросопротивления для задачи мониторинга криолитозоны Геофизические исследования, - (year - 2024)

6. Nikitenko M.N., Glinskikh V.N., Mikhaylov I.V., Fedoseev A.A. Мониторинг состояния криолитозоны методом импульсного электромагнитного межскважинного просвечивания Геомодель 2023: 10-я международная конференция "Геонауки: время перемен, время перспектив": сборник материалов конференции (г. Санкт-Петербург, Россия 17-20 апреля 2023 г.), Геомодель 2023: 10-я международная конференция "Геонауки: время перемен, время перспектив": сборник материалов конференции (г. Санкт-Петербург, Россия 17-20 апреля 2023 г.). ООО "Геомодель", 2023. 5 с. (year - 2023)

7. - В ИНГГ СО РАН создают новую технологию для мониторинга вечной мерзлоты Наука в Сибири, Официальное издание СО РАН "Наука в Сибири", 1 июня 2023, № 22, с. 7. (year - )

8. - Ученые разрабатывают электромагнитную технологию для мониторинга вечной мерзлоты Портал о развитии Арктики — GoArctic.ru, - (year - )

9. - Новую технологию мониторинга вечной мерзлоты предлагают новосибирские ученые Интерфакс, - (year - )

10. - Новая технология для мониторинга вечной мерзлоты Портал Российской академии наук, - (year - )