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We have compiled maps of areal isotope composition changes and constructed graphs of gas HC distribution depending on the stratigraphic age of the host rocks and graphs of isotope composition changes depending on the depth of sampling to study the hydrocarbon potential of the deep-seated oil and gas pools of the South Caspian Basin. The genesis of gas was studied using the techniques elaborated by M. Schoell and A. James. Two stages of hydrocarbon formation have been established by study of various kinds of gas manifestation. The first stage (Miocene-Eocene) began in the deposits underlying the Productive Series and continued up to the deposits of the latter. This stage was characterized by a frequent change in the directions of both downward and upward movements of gases. The second stage of hydrocarbon formation (Anthropogene-Pliocene) began in the deposits of the Productive Series and was characterized by a change in the regional geodynamic setting. Avalanche sedimentation and the predominance of downward movements over upward ones favored the accumulation of thick sediments at the time when the Productive Series formed. The sedimentation and tectonic processes (downwarping) in the deep-water zone of the basin led to harsh thermobaric conditions in the sedimentary strata. A detailed analysis of the results of gas survey in the deep-water zone of the South Caspian Basin has shown gas generation with a predominance of two components, methane and ethane. Study of the trends of temporal and areal hydrocarbon migration and of the areas of oil and gas generation makes it possible to reveal structures with evidence for large and giant hydrocarbon reserves. We have established that gas hydrocarbons in the bottom and upper-section sediments of the southern Caspian Sea are intimately related to the sources of hydrocarbons, their migration, and other processes running in the deep-seated sediments and in the upper section.

The three-dimensional dynamic problem solution of the theory of elasticity as it applies to modeling of all types of seismic waves propagating in real geological media is considered. The elements of the 3D forward modeling algorithm based on the spectral element method (SEM) for the numerical solution of the problems posed are presented. The SEM’s main characteristics (high order spatial discretization, explicit time integration scheme) and its advantages are compared with the classical finite element method (FEM). Distinctive features of massively parallel implementation of this algorithm on NVidia’s GPU using CUDA (Compute Unified Device Architecture) are considered. The efficiency of parallelization on hybrid systems at different orders of SEM and parameters of the numerical scheme of time integration is analyzed. Results of solving a three-dimensional problem of modeling seismic wave propagation in a heterogeneous geological medium with faults and strongly varying (vertically and horizontally) properties of the investigated layers are presented. A highly detailed digital geological model constructed for one of the petroleum fields in the Arctic region using Petrel, the world’s most popular geological modeling tool, is used as input datasets. The problem was solved on a mesh of hexahedral elements in 3D to perform efficient SEM calculations in the CAE Fidesys software developed earlier with the authors participation for engineering simulations (strength analysis, etc.). The derivation of the model was based on the typical seismogeological conditions of Western Siberia so that the modeling allows investigating look-ahead capabilities of numerous seismic exploration methods for an in-depth study of major oil-and-gas-bearing complexes in this region. The prospects of model implementation for other candidate regions with different geological structure are equally promising. Outputs of the full-waveform seismic modeling is stored in the standard SEG-Y format currently widely used worldwide in industry for seismic data processing. The obtained synthetic seismograms and seismic wave fields are analyzed. The practical significance of the conducted research whose results can be utilized in the future for solving a wide range of applied tasks for regions with different geological conditions is deduced.

For the territory of the Middle Urals segment, a high-resolution grid density model of the upper part of the lithosphere was constructed (grid step is 500 m) to the depth of 80 km - the first regional level of isostatic compensation. The spatial framework of density sections serves as the basis for a three-dimensional (3D) interpolated density model - an initial approximation model. The corrections to the density model of the initial approximation are found from the solution of the linear inverse gravimetry problem of practically meaningful correctness sets of density equivalents. The fairly thin horizontal layers of the grid density model are selected as such sets. The method and technology to calculate 3D density distribution with reference to 2D data along reference seismic sections are embedded in the methodology for quantitative interpretation of potential fields with the construction of 3D geophysical models. The relief of the internal boundary surfaces of the upper, middle and lower crust is compared to the structural scheme of tectonic zoning along the surface of the basement. To construct tectonic schemes, lithostatic pressure anomalies are also used; they are calculated from a general integral characteristic - the mass of density columns from the earth’s surface to a given depth. Anomalies of lithostatic pressure for each layer of a 3D grid density model are proportional to excessive density within the layer, so that a density model is easily converted into a lithostatic model. 3D anomalies of lithostatic pressure clearly configure the block structure of the earth’s crust at different depth sections. In the projection at the surface of the middle and lower crust, the contours of lithostatic anomalies correspond to the tectonic zoning scheme of the basement, built based on potential fields. A comparison of ‘block diagrams’ of density and lithostatic models is used to identify structural elements of different order of deep tectonic zoning at different depth sections.

An analytical model δ(sur) is suggested for nitrogen and oxygen shift coefficients of water vapor in the visible region. The model δ(sur) linearly depends on the broadening coefficient of a given line and fitted parameters. The analysis of the available experimental data on d coefficients for the near infrared and visible regions is performed. The model δ(sur) retrieves 486 nitrogen shift coefficients for lines from the range 13550-22590 cm^-1 with a mean square deviation of 6.0 × 10^-3 cm^-1/atm and oxygen shift coefficient for lines from the range 13550-14000 cm^-1 with a mean square deviation of 2.5 × 10^-3 cm^-1/atm.

In the context of modern climate change, permafrost degradation from the surface takes place in Western Siberia. This is manifested by an increase in temperature and a decrease in the area of distribution and thickness of frozen layers. To establish the rate of reduction in permafrost area, a cartographic model was created to predict the change in the position of its southern limit by the middle of the 21st century. Based on temperature, ice content, rock composition, and section structure data, permafrost areas were ranked concerning the thawing rate of the upper 10-m-thick permafrost layer. It was found that the expected change in the southern limit of permafrost in Western Siberia will be uneven and dependent on the local conditions related to the cryolithogenic foundation of the landscape.

This article discusses the results of retrospective verification of the strength prediction model for saturated rocks of southern Yakutia. The model was developed for the geotechnical conditions of the city of Neryungri. The input data for the model consisted of the decay rate coefficients of the harmonic field of a vertical magnetic dipole measured at a 1.125 MHz frequency using the geometric electromagnetic induction sounding method. The error of model predictions was close to the allowable error of ±20 % for average laboratory estimates of rock sample strength and ranged from ±16.8 to ±33.5 % for different site conditions with a probability of about 70 %. The total error of the model at this probability is 27.2 % with maximum outliers overestimating the laboratory strength of weak rocks by 120.5 % or underestimating the strength of strong rocks by 86.8 %. The model predictions were more accurate (errors of 22.8 and 21.9 %) for the rock masses composed predominantly of moderately strong (15-50 MPa) and strong (50-120 MPa) rocks. The statistical results indicate that the model is regionally representative and can be applied in the areas of warm and cold permafrost sedimentary rocks of southern Yakutia for rapid, cost-effective terrain evaluation by rock strength.

The purpose of this work was to specify the hydrogeological conditions in the poorly studied northeastern part of the Lena-Amga interfluve. We analyzed archival (1965-1995) and published data on subpermafrost waters and permafrost thickness in the Churapcha and Tattinsky districts of the Republic of Sakha (Yakutia), including new field studies (2009-2022). The research was based on the data from 19 groundwater exploration wells, 450 to 650 m in depth. It is shown that the Jurassic and Middle Cambrian aquifer complexes differ in piezometric pressures and chemical composition. Based on the new information, it is suggested that the boundary between these two aquifer complexes should be shifted northward by 50-80 km. A zone with distinct specific hydrogeological conditions confined to the Tatta-Tompo fault was identified. Presumably, the fault was formed under conditions of horizontal compression, which resulted in the compaction of the rocks and their reduced permeability along the fault, as well as in the increased freezing intensity in the strata with a low water content during periods of decreased global temperatures.

Natural gas hydrates exist in porous media under high pressure and low temperature conditions, including permafrost. The development of methods for calculating the phase equilibria in hydrate-bearing soils and sediments is of great interest. This includes the equilibrium content of nonclathrated water, as pore water in equilibrium with pore hydrate and under given thermobaric conditions. Nonclathrated water is similar to unfrozen water in frozen soil. The current study focuses on thermodynamic relationships for calculating nonclathrated water content in soil under certain thermobaric conditions based on experimental data of pore water activity and soil water content. It has been shown that at a constant temperature the nonclathrated water content decreases sharply according to a power law as gas pressure increases. The results of thermodynamic calculations are in agreement with direct measurements of nonclathrated water in soil systems using the contact method. Thus, at temperatures below 0°C, the nonclathrated water content decreases by more than two times in kaolinite clay and in sandy clayey soils with an increase in methane pressure from 2.3 to 11 MPa. The obtained relationships allow us to recalculate the nonclathrated water content after transition from one hydrate-forming gas to another, as well as calculate nonclathrated water content using the unfrozen water content curve at different temperatures. Developed thermodynamic approach can be applied to various hydrate-forming gases and their mixtures.

Climate change affects the parameters of snow cover, including the distribution of snow storage on plain territories under forests and in fields. A comparison of the average long-term maximum snow storage in forests and fields for different climatic periods is carried out. The average value of snow storage on fields for the current climatic period (1991-2020) increased by 4 % compared to the period 1966-1990; in forests, it decreased by 6 %. Average snow storage in forests and fields in 2001-2010 amounted to 127 and 123 mm; in 2011-2020, it decreased to 121 and 120 mm, respectively. The ratio of snow storage in forests to its value in fields - the snow accumulation coefficient - for 1966-1990, 1981-2010, and 1991-2020 has been constantly decreasing and amounted to 1.16, 1.08 and 1.05, respectively. Maps of the distribution of snow storage and the coefficient of snow accumulation within plain territories of Russia for different climatic periods have been constructed. The tendency of leveling the maximum snow storage in forests and fields under the modern climate (1991-2020) has been confirmed.

The main stages in the development of geocryology in the XX-XXI centuries are highlighted. The major research achievements are presented in the fields of permafrost science, permafrost engineering, historical geocryology and regional geocryology. The most important results of research at the Melnikov Permafrost Institute of the Siberian Branch of the Russian Academy of Sciences are described.