This paper is dedicated to the topical problem of examining permafrost’s state and the processes of its geocryological changes by means of geophysical methods. To monitor the cryolithozone, we proposed and scientifically substantiated a new technique of pulsed electromagnetic cross-well sounding. Based on the vector finite-element method, we created a mathematical model of the cross-well sounding process with a pulsed source in a three-dimensional spatially heterogeneous medium. A high-performance parallel computing algorithm was developed and verified. Through realistic geoelectric models of permafrost with a talik under a highway, constructed following the results of electrotomography field data interpretation, we numerically simulated the pulsed sounding on the computing resources of the Siberian Supercomputer Center of SB RAS. The simulation results suggest the proposed system of pulsed electromagnetic cross-well monitoring to be characterized by a high sensitivity to the presence and dimensions of the talik. The devised approach can be oriented to addressing a wide range of issues related to monitoring permafrost rocks under civil and industrial facilities, buildings, and constructions.

—The work deals with the development of methodological and algorithmic tools for the quantitative interpretation of oil well resistivity logs. We review the results of applying the neural-network-based approach to the inversion of resistivity logs measured at thinly bedded high-contrast environments. The capabilities of the proposed approach are demonstrated by the example of the algorithm for noninterative express inversion of unfocused lateral logs (BKZ). BKZ is the unfocused array logging method widely used in the Commonwealth of Independent States for oil well studies. BKZ logs are known for their complexity: The signals of unfocused gradient probes are highly affected by the medium properties below and above the measuring point. The developed algorithm is based on the inversion of full logs into the parameters of a 2D axisymmetric model of the medium, which allows naturally taking into account the influence of surrounding rocks and borehole conditions. Transition from the “layered” parametrization conventional for BKZ logs interpretation to a quasi-continuous change of properties along the well axis allows extracting meaningful information at every measurement point and constructing high-resolution geoelectric models of the sediments. The noniterative nature of the algorithm provides a high computing efficiency. This opens up the possibility of using the 2D inversion advantages to increase the reliability of the initial express interpretation results. Testing the algorithm on the practical data from West Siberian oilfields has revealed the field of its maximum efficiency, namely, study of impermeable and low-permeability sediments, such as the complex shaly caprocks and bituminous deposits of the Bazhenov Formation. With high-quality input data, the approach is also efficient for studying permeable terrigenous sediments.

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.

—The work is devoted to the theoretical substantiation of a new geophysical technology for studying a unique geological object with unconventional hard-to-recover hydrocarbon reserves. The technology is based on transient electromagnetic sounding from a spatially distributed system of highly deviated wells drilled in target objects near the Bazhenov Formation. The results of computer modeling predetermine a new direction for geological exploration of unconventional hydrocarbon deposits. We consider a numerical solution to the 3D direct problem of pulsed electromagnetic sounding and, on its basis, develop a computational scheme and computer program. A mathematical model is built that describes the sensing process through a pulsed source for electromagnetic field excitation. The Fourier transform is used for time discretization, and the vector finite element method for spatial discretization. This approach makes it possible to obtain many independent 3D problems and effectively solve them in parallel by applying the modern multiprocessor technology. Using the KNL and Broadwell computing nodes of the Siberian Supercomputer Center SB RAS, we performed calculations of electromagnetic signals, which showed a high efficiency of the devised computing scheme and a high performance of the implemented algorithm. Despite the fact that the total peak performance of the KNL nodes is 2.5 times higher than that of the Broadwell nodes, their practical application for performing large-scale 3D modeling on the cluster shows a high efficiency of the latter. When choosing the most suitable computing architecture for the implementation of mass calculations, one should not rely on their formal characteristics only; significant performance is achieved taking into account the peculiarities of the computational methods employed for solving a specific problem. The implemented more efficient ways of performing parallel matrix-vector operations did not significantly increase the performance for this computational scheme. The created computational tools form the basis for further design of the configuration of a pulsed electromagnetic sounding system, and for identifying the capabilities of the new geophysical technology for examining complex geological media.

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. At the same time, non-stationary electromagnetic methods seem to have significant potential and a number of important practical advantages. We propose a cross-borehole exploration system for the highest localization of target objects in the cryolithozone. A novel mathematical apparatus for three-dimensional modeling of transient electromagnetic (TEM) 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 have studied the sensitivity of the TEM signals to the boundary between thawed and frozen rocks depending on the inter-borehole distance and spatial orientations of the transmitters and receivers. Numerical simulation results of the TEM monitoring of industrial facilities located on permafrost are considered. 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.