Background. The research object was the Lower-Cambrian Abakunskaya Formation located in the South-Tunguskaya oil-and-gas bearing region of the Lena-Tunguskaya oil-and-gas province.

Aim. To compile a sedimentary-capacity model of the Abakunskaya Formation and identify relationships between the identified lithological rock types and their filtration-capacity properties in order to refine the oil and gas potential of the region.

Materials and methods. Geological and geophysical data collected from deep wells drilled in the area of work were used, along with published and archival materials on the geological structure of the South Tunguska oil and gas region. The factual material on 24 wells that opened the Abakunskaya Formation includes descriptions of cores, sludge, and test results. The wells were drilled in 1970—1990; however, detailed descriptions of the core material, core photographs, and core study results, with some contradictory exceptions, are missing. For this reason, the Formation was sectioned based on GIS materials with an analysis of all preserved materials on the wells. Logging diagrams for 20 wells were analyzed. An analysis of changes in the thickness and composition of sediments was carried out. A detailed division of sections into members, correlation of sections, and analysis of changes in the filtration and storage properties of rocks were performed. The developments of the specialists of the All-Russian Research Geological Oil Institute (VNIGNI), which comprise a system of genetic organization of carbonate bodies of various hierarchical levels, served as the methodological basis for this research.

Results. Lithological types of sediments were determined; lithotype associations characterized by common sedimentation conditions were identified; lithological-facies zones were distinguished; and a sedimentation-capacity model of the Abakunskaya Formation was compiled.

Conclusions. The Abakunskaya Formation is represented by carbonate and carbonate-clay deposits of the open-shelf lithological-facies zone, which are relatively consistent in thickness and composition. A sedimentary-capacity model of the Abakunskaya Formation in the western part of the South Tunguska oil-and-gas bearing region has been constructed. This model reflects changes in the composition and thickness of the deposits, as well as their structural and textural charac- teristics. Oolitic-organogenic-clastic types of carbonates that form accumulative bodies exhibit the highest filtration and capacity properties.

Background. The Gunashli field located at a depth of 80–300 m in the deep-water part of the Caspian Sea represents another hinge undulation of the Absheron-Balkhan tectonic zone to the southeast of the Oil Rocks field.

Aim. To study the Lower Pliocene deposits as a productive area (PA), i.e., the main object of oil and gas content.

Materials and methods. The calculation of oil and gas reserves of the Gunashli field mainly include the volumetric method formula with six parameters. One of the main parameters is the net pay thickness (NPT), which is the ratio of the volume of pores, voids and caverns saturated with oil to the total volume of the rock.

Results. Similar to the adjacent areas, the PA is lithologically represented by alternating layers of sand, sandstone, silt, and clay of varying thickness. The main developed object is the Fasilya suite and X horizon of the Balakhan suite, which contain 90% of the oil from total field reserves. Based on the constructed maps, the weighted average NPT values of the Fasilya suite and X horizon of the Balakhan suite are calculated for the blocks of the field. The NPT is one of the main parameters significantly affecting the error in determining hydrocarbon reserves. The NPT value determined in this study by two methods of arithmetic and weighted means significantly differ by 15–20%. The hydrocarbon reserves of the Gunashli field for the Fasilya suite and X horizon are assessed using weighted average NPT values.

Conclusion. NPT values can be used for determining the direction of improving petrophysical properties of rocks and number of projected wells, as well as for predicting the phase states of hydro- carbons at the stage before field exploration.

Background. The validity of initial deposit assessment largely depends on the accuracy of water saturation determination. The saturation exponent (n) is an important parameter included in the majority of generally accepted integrated models for determining water saturation. The error of saturation determination at the level of 0.5 may distort the final estimate of water saturation by 30%. It is believed that the Resistivity Index (RI) is affected not only by the coefficient of current water saturation (Sw) but also by such factors as wettability, reservoir water mineralization and its ionic composition, as well as the amount and mineral composition of clays.  

Aim. To assess the effect of cation exchange capacity and mineralization on the saturation exponent of Cretaceous clayey rocks from a Western Siberian field.  Materials and methods. The research objects were 23 core samples alternately saturated with model formation water of different mineralization and composition. The samples were collected from Cretaceous deposits in a Western Siberian field located in the Middle Ob oil-gas area. The experiments were conducted in the modes of full and partial water saturation.  

Results. The influence of cation exchange capacity, as well as the mineralization and composition of the model formation water, on the saturation exponent is absent. No change was found in the effect of ‘bound’ water on the rock conductivity depending on changes in the current water saturation.  

Conclusion. Knowledge of the influence of the mineralization and composition of reservoir water, as well as cation exchange capacity, on the Resistivity Index is important for assessing the risks of inaccurate determination of saturation exponent (n) during standard laboratory studies using sodium chloride models of reservoir water of a single mineralization.  

Background. Hydrocarbon deposits in Niger have been actively explored since the 1970s. However, oil production only commenced in 2011 with the discovery of the Agadem oil field. The available hydrocarbon resources of this region are currently underestimated; thus, it is relevant to forecast the territory for oil and gas content using modern integrated geological and geophysical methods and studies. To that end, the available hydrocarbon systems in the region, including source rock formations, reservoir rocks, sealing rock, reservoir traps should be determined. Additionally, the way these elements are related to each other should be studied. This article examines the source rock formations of the Termit Basin in the Republic of Niger. The region is of considerable interest due to the oil and gas prospects of the Yogou Formation.

Aim. To examine the geochemical characteristics of the Yogou Formation through identifying the organic matter source of the Yogou Formation mudstones, as well as specifying the predominant phase composition of hydrocarbons generated by mudstones of the Yogou Formation.

Materials and methods. Samples of the Yogou Formation mudstones from nine wells located in the Agadem Block of the Termit Basin were used. The results of pyrolytic, petrographic, and biomarker studies of the Yogou Formation source rock kerogen obtained from stock materials, published pa- pers, and reports provided by the Ministry of Petroleum Resources of the Republic of Niger, were analyzed.

Results. Petrographic analysis performed by the China National Petroleum Corporation revealed that the kerogen of the source rocks of the Yogou Formation has a maceral composition including vitrinite, inertinite, and liptinite, particularly leptodetrinite, sporinite, cutinite, and resistinite. Analysis of the biomarker content of the extracted samples of the Yogou Formation showed that C27-C28-C29 steranes are present in the extracts with a predominance of C29 steranes over the common C27 and C28 steranes. According to the initial hydrogen index values determined by Rock-Eval pyrolysis, the predominant source for organic matter was higher vegetation.

Conclusion. The organic matter of the rocks of the Yogou Formation was originally derived from higher terrestrial vegetation. Consequently, the source rocks will generate more gaseous hydro-arbons.

Background. Eocene sediments are considered one of the key oil source strata that shape the hydrocarbon potential of the South Caspian Basin. Geochemical studies on adjacent land have confirmed the universally high generation properties of Eocene sediments. However, within the Caspian Sea, these strata occur at significant depths and have not been penetrated by wells or studied using geochemical methods. Under these conditions, the geochemical parameters of Eocene sediments in the basin can only be estimated by analogy with those in adjacent land areas, based on established and predicted lateral patterns and facies zonation of paleobasins.

Aim. To perform paleogeographic reconstructions of Paleocene-Eocene sedimentary basins in the Caspian–Caucasus region, analyze the sedimentation conditions and formation of the generation properties of Eocene sediments, and predict their geochemical characteristics, including in the South Caspian.

Materials and methods. The study employed data from published and archived large- and small-scale lithological and paleogeographic maps, rock composition and geochemical properties, as well as those on the actual petroleum potential of the Paleogene interval of the section. Regional-level paleogeographic reconstructions were developed based on lithofacies characteristics and rock thickness maps developed by the authors. The resulting paleogeographic models were used to extrapolate the generation properties and predict the geochemical characteristics of Eocene deposits within the Southern Caspian Sea.

Results. The paleogeographic reconstructions allowed us to characterize the main developmental features of Eocene sedimentary basins in the Caspian–Caucasus region and identify major sedimentation facies zones favorable for the formation of oil source strata. Based on a combined analysis of paleogeographic and geochemical data, a forecast of the petroleum source properties of Eocene sediments and the possible range of their geochemical parameters in the Southern Caspian Sea was made.

Conclusion. The conducted study demonstrated that the petroleum source properties of the regional Eocene source strata are controlled by its facies features. Carbonate Eocene sediments, formed under favorable reducing conditions in a shallow basin, possess a high generation potential and are a key source of liquid hydrocarbons in the Caspian–Caucasus region. In deep-water basins of the Eocene basin with high sedimentation rates, including the South Caspian Depression, a deterioration in the petroleum source properties of sediments is predicted as a result of dilution of the terrigenous component of marine organic matter. However, even taking into account the deterioration of the initial generation potential of rocks within the modern water area compared to areas of adjacent land, there is a high probability of the presence of oil source strata with satisfactory properties in the water area of the South Caspian.

Background. The Fan–Yagnob syneclise is a large Meso-Cenozoic structure overlapping the Paleozoic folded structure of the Zeravshan–Gissar region of Central Tajikistan. From 1933 up to the present, the conducted geological explorations have identified 81 deposits and 522 ore occurrences. Among them are Jizhikrutskoye and Takfonskoye, which are located in the vicinity of the syneclise under consideration. There are eight mining districts within the boundaries of this metallogenic region, including Fandaryinsky (Au with W, Sn, Mo, Bi), Matchinsky (Sb–W–Au with As, Sb, Bi, Mo, Pb, Zn, Sn, Cu, Ag), Yagnobsky (Sb–W–Sn–Au with As, Sb, Hg, Pb, Zn, Mo, Cu, Bi, Se, Tl, Ag), Varzobsky (W with Sn, Cu, Bi, Zn, Cd, Tl, Se, In, Ag), Iskanderkulsky (Hg–Au with As, Ag), Archamaydansky (W–Bi–Pb–Zn–Sn with Cu, Ag, Au), Shing Magian (Sb–Hg–Ag–Au with As, Zn, Pb, W, Pb–Zn, Bi, Se, Te), Pravoberezhny Zeravshan (Hg–Au with As and Ag). During the Permo-Triassic period, Central Tajikistan underwent intense denudation, during which the depth of the erosion section of the deposits reached about 2 km. The areas of accumulation were the Fan–Yagnob syneclise and other similar structures of the Upper Mesozoic floor. The Fan–Yagnob syneclise was highly likely to accumulate dispersed ore matter from eroded Paleozoic deposits. The article presents facts confirming this assumption.

Aim. The purpose of this study is to substantiate the source of matter from the Paleozoic ore deposits of the Zeravshan-Gissar metallogenic zone for the formation of placer and chemogenic metal concentrations in the Fan-Yagnob Mesozoic syneclise. Research object. The Fan-Yagnob Mesozoic syneclise and the Zeravshan-Gissar Paleozoic mountain-fold region serve as the boundaries of a significant group of ore deposits of various metals.

Materials and methods. The article is based on: 1) publications by our colleagues; 2) the use of a comparative analysis of numerous ore deposits within the boundaries of the Zeravshan-Gissar metallogenic region; 3) rock material selected and analyzed by the authors using a portable X-ray fluorescence spectrometer Vanta-M (Olympus, USA) with a 4-watt Rh anode, 50-kilovolt voltage, and an SDD detector that can detect petrogenic and ore elements with a sensitivity of up to 10^-4%.

Results. The prospects of Mesozoic terrigenous deposits of the Fan-Yagnotsyan syncline for the localization of Paleozoic ore minerals displaced by denudation are substantiated.

Conclusion. The Fan-Yagnob Mesozoic syneclise is an area of accumulation of not only terrigenous and biogenic matter (coal deposit), but also a large group of ore elements that may have practical significance.

Background. Effective planning of gas and gas-condensate fields requires an integrated approach, which could ensure maximal economic effects while observing the conditions for the rational use of hydrocarbon reserves of the field. This includes not only effective technological solutions for field development, such as the number of wells and development systems, but also the optimal design of the entire infrastructure.

Aim. To develop a methodology for optimizing the placement of production wells, well pads, and booster compressor stations (BCS) taking into account technological, economic, and geographical constraints.

Materials and methods. The proposed approach is based on mathematical modeling, including an analysis of the density of reserves in the reservoir for the most competent placement of design wells, accounting for the costs of infrastructure construction and minimizing the costs of gas transportation. Additionally, landscape constraints affecting the placement of infrastructure facilities are considered.

Results. The developed approach allows the amount of hydrocarbon reserves involved in development to be maximized and the capital costs for infrastructure construction and operating costs to be minimized, which constitutes the key task of gas field planning.

Conclusion. The developed methodology and its software implementation can be used in the design of new gas condensate fields, as well as for optimizing the development schemes of existing facilities.

Introduction. The analysis and processing of signals with complex structures — particularly those exhibiting frequency and phase modulation — remains a relevant challenge, especially in cases where traditional methods fail to provide sufficient accuracy. This study considers a modified Fourier transformation suitable for processing signals with modulated frequency and phase, referred to in the article as frequency-phase modulated (FPM) signals.

Objective. To develop and apply a modified Fourier transformation for obtaining the amplitude-frequency characteristics (AFC) of FPM signals, aiming to improve the accuracy of signal fitting and to address problems related to modeling the responses of complex systems.

Materials and methods. The proposed transformation is applied directly to FPM signals and, due to its strictly periodic structure, enables the accurate determination of their AFC. The method was tested on gravimetric data acquired using the GNU-KB and CG-6 gravimeters. These data represent detrended temporal fluctuations of the gravity field, which are typically difficult to describe and interpret using conventional methods.

Results. It has been demonstrated that the proposed transformation effectively addresses the problem of determining the AFC of FPM signals, including those embedded within the transformation itself. The results show a high degree of fitting accuracy, thereby offering new opportunities for analyzing the responses of complex systems without the need for detailed physical modeling.

Conclusion. The modified Fourier transformation may serve as a valuable tool for constructing fitting functions in the form of AFCs when studying complex systems. In gravimetry, this approach opens new prospects for both fundamental research and the solution of applied geological and geophysical problems.

Background. The resistivity method of electromagnetic survey has a long-recognized problem associated with the need for reliable grounding of measuring electrodes, which is difficult or impossible in conditions of permafrost, rocky soils, snow cover, or artificial surfaces. Contactless measurements solve this problem and speed up the survey process. However, the theoretical justification for this approach is historically based on approximate methods rather than rigorous solutions.

Aim. To theoretically substantiate the technique of contactless measurements in the resistance method using rigorous forward solution of electrodynamic equations. The study aims to analyze the components of the electromagnetic field and determine the optimal conditions for the correct assessment of the specific electrical resistance (SER) of soil.

Materials and methods. The study is conducted using the mathematical simulation of two medium models: two-layer (air–conductive half-space) and three-layer (air–intermediate layer–conductive half-space). The simulation is performed for a low-altitude dipole-axis array at an AC frequency of 16 kHz. The field calculation is based on a rigorous solution to the system of electrodynamic equations. The amplitude of the total electric field strength Ex and the modulus of the reactive component Re Ex are analyzed.

Results. The standard approach using the amplitude of the total field E_x to calculate the apparent SER (ρ_a) at small spacings gives anomalously high values independent of ρ₂ due to the field effect of charges at the ends of the current dipole. In contrast, the calculation of ρa based on the reactive component Re Ex excludes this effect. For a two-layer model, an optimal spacing of 8—10 m was established to provide the best match between ρ_a and ρ₂. For a three-layer model, the high-SER layer is equivalent to an increase in the height of instrument lift, while the layer with low resistivity significantly complicates the interpretation.

Conclusion. An advanced approach to contactless measurements in the resistance method using the reactive component of the electric field is developed and substantiated. This approach increases the reliability of determining the specific electrical resistance of underlying rocks. The results of the study open up prospects for the development of effective equipment and methods for contactless electromagnetic survey applicable in complex grounding conditions.

Background. One common problem in in-situ leaching (ISL) involves the formation of sand plugs in the filter zone and wellbore of production wells, which significantly reduces their productivity. Existing methods of plug removal, such as bailing or flushing, as well as the use of submersible centrifugal pumps and airlifts, have significant drawbacks, including low efficiency, abrasive wear, or limitations of well depth and diameter.

Aim. To increase the efficiency of ISL wells by removing sand plugs using an ejector (hydraulic elevator).

Materials and methods. The study is based on hydraulic calculations of jet devices in a pipe-in-pipe system. The well depth, pressure losses and geometric parameters of the hydraulic elevator are taken into account.

Results. The most effective hydraulic elevators have a small value of the geometric parameter (m=2–3). The optimal configuration with a 76 mm outer column and a 50 mm inner column reduces pressure losses and pump pressure at a depth of 400 m to 20 m H₂O and 11.0 MPa, respectively.

Conclusion. The use of ejectors is an optimal method for removing sand plugs.

Background. The extraction and processing of minerals is a vital industry that plays an irreplaceable role in the global economy. It provides industry with mineral resources, stimulates technological progress and facilitate the economy transition to environmentally friendly technologies. As the world moves toward a green and digital future, it becomes increasingly important to meet changing demand for mineral resources, which simultaneously places new demands on the environmental sustainability and social responsibility of enterprises operating in the subsoil management sector. For the mining industry, these demands can be met through the implementation and integration of advanced energy-saving technologies and breakthrough digital innovations with efficiency largely dependent on the effectiveness of the enterprises’ management system.

Aim. To improve the management of transition to green and digital technologies for participants of the subsoil management sector; to study the factors affecting these processes.

Materials and methods. The methods of this study include analysis, synthesis, comparison, generalization, and systematization.

Results. The sources of greenhouse gases typical of mining operations are investigated. The essence and objectives of the transition of the subsoil management sector to green and digital technologies are outlined; specific components and stages of this process are highlighted. The importance of digital innovation for the implementation of environmentally friendly technologies in the mining industry is noted. The key determinants of green and digital transition in subsoil management are described. The presented organizational and institutional mechanism for managing this process ensures a harmonious transition to environmental sustainability and digital innovation in the subsoil management system. Particular emphasis is placed on promising resource-saving technologies that can support this transition.

Conclusion. The present article proposes a concept of intelligent management for the green and digital transformation of the subsoil management system, which is designed to promote operational efficiency and carbon neutrality, as well as to minimize the adverse impact of natural resource extraction on society and environment. The practice of the Polymetal JSC (Saint Petersburg, Russian Federation) in improving environmental sustainability through the use of contemporary technologies is analyzed.

Background. The growing relevance of using numerical or analytical methods for solving engineering and geocryological problems in the permafrost zone is increasingly raising questions about determining input parameters. In the present-day practice, thermal properties of soils can be determined using numerical methods in addition to laboratory tests. The search for universal dependencies that most accurately describe the thermophysical properties of frozen soils is becoming an important task of modern research. This study considers models for assessing thermal conductivity of soils, taking into account the physical properties, mineral composition and water content of dispersed soils. These models have become widely used, primarily in foreign practice and contemporary software for thermophysical simulation.

Aim. To consider a method for using thermal conductivity models taking into account the physical properties, mineralogical composition and water content of frozen dispersed soils with the purpose of assessing their effectiveness.

Materials and methods. Two models for assessing the thermal conductivity of dispersed frozen soils are analyzed. A statistical analysis of their effectiveness is performed based on a sample of twenty experimentally determined thermal conductivity values of sandy and clayey non-saline, non-peaty frozen soils.

Results. The efficiency of using thermal conductivity models is at a satisfactory level. The expected values of thermal conductivity in a frozen state are predicted with greater accuracy compared to the method adopted in domestic practice. The most preferred methods considering the thermal conductivity of particles are determined.

Conclusion. A combination of physical properties, mineralogical composition, and unfrozen water content in the given models has clear advantages. A further study of this issue is necessary to expand the number of compared models and soil sample. The importance of considering the mineralogical composition in the assessment of thermal conductivity for dispersed frozen soils is demonstrated.

Background. Landslides represent an exogenous geological process (EGP) most intensively developed in mountainous areas, leading to human casualties and enormous property losses to the existing infrastructure of the area. Son La is a mountainous province in northwestern Vietnam that is frequently affected by landslides. The present research work observes the correlation between natural and anthropogenic factors, as well as the spatial distribution of landslide phenomena in Son La province; a set of preventive anti-landslide measures and solutions is proposed.

Aim. To assess the role of factors and conditions affecting the degree of landslide activity in the province of Son La and to propose measures preventing or minimizing the negative impact of land-slide processes on the environment.

Materials and methods. To achieve this objective, the authors employed the analysis and processing of field research data, as well as the modified frequency ratio (MFR) method in combination with GIS technologies. Thus, the frequency ratio value (weight) for each studied factor that determines the presence and degree of landslide activity was determined; remote sensing was used to identify the representativeness of the factors.

Results. The studies and assessment of the role of factors influencing landslides in Son La province show that their significance in descending order is as follows: land use; altitude above sea level; distance to roads; stratigraphic and genetic complexes and suites; distance to erosion network; slope steepness; slope exposure; distance to geological and tectonic faults; average annual precipitation. All listed factors are ranked by the prediction rate (PR). Among them, land use has the greatest effect on the degree of landslide activation in Son La province. In addition, a set of measures is proposed to prevent or minimize landslide processes in the studied area.

Conclusion. The results of the present study provide an important scientific and practical basis for assessing the stability of the geological environment in Son La province, helping local authorities to rationally use the territory and take into account the landslide situation in the general planning of the socio-economic development of the province.

Background. The article examines and discusses a possible scenario for the formation and development of the Caspian Depression as a result of fragmentation of the southeastern corner of the East European Platform and the advancement of a rigid block — Ustyurt — from this platform along a three-ray fault system.

Aim. To reconstruct the history of formation and geological development of the Caspian Depression.

Materials and methods. The authors’ own data, as well as numerous publications on the problem of geological structure and geological development of the area under study, were used.

Results. The study reconstructs the evolution of the Caspian Depression from the formation of the marginal basin sea of Paleotethys toward a platform syneclise. The advancement of the rigid block — Ustyurt — led, upon the removal of the load, to the uplift of the entire southeastern part of the platform and denudation of pre-Devonian deposits. These deposits are partially and strictly locally were preserved as relics in graben-like depressions and on the slopes of the newly formed deep-water depression. During the movement of this block toward the east or southeast, individual blocks split off therefrom, on which, as shoal areas, isolated carbonate platforms and reefs were formed. At the end of the Early Permian, in connection with the closure of Paleotethys, a marginal basin sea formed in the place of the modern Caspian Depression. It was isolated from the east by the mountain structures of the Urals, from the south — by the Karpinsky Ridge and dislocations within the modern Mangyshlak. Under arid climate conditions, this led to the formation of a thick salt-bearing stratum of the Kungurian stage, which filled the deep-water depression.