The article presents the results of the study of dictyonema shales of the Baltic basin (Leningrad Oblast, Kaibolovo-Gostilitsy prospecting area) for uranium (updated data on uranium mineralization of dictyonema shales) and rare earth elements (for the first time – as a new promising raw material source). At the same time, updated author’s data on the total metalliferous content of dictyonema shales was made In relation to uranium, its average content in dictyonema shales has been clarified, the distribution of uranium in the section of sedimentary strata according to new well profiles has been given, and the features of its distribution have been clarified, in comparison with earlier authors’ publications on this object of research. For rare earth elements in dictyonema shales, the results on their concentrations on a much larger analytical material are presented (670 samples, instead of 88, data on which were published earlier). For the first time, the features of the distribution of rare earth elements over the prospecting area and in the section of sedimentary strata along the profiles of wells are illustrated. New data on the petrographic composition of dictyonema shales are presented. An additional study of mineral impurities of dictyonema shales was carried out using a new method of areal scanning of preparations with an electron probe microanalyzer using the “Feature” software module. The correlations between the concentrations of uranium and rare earths with other micro- and macroelements, the forms of uranium and rare earth elements in dictyonema shales, geochemical indicators, conditions and genesis of the formation of uranium and rare earth mineralization developed in them was clarified. Based on an earlier assessment of the resource potential of uranium and rare earths, a modern assessment of their prognostic mineral resources and possible recoverable industrial reserves and the cost of potential ore raw materials of the studied acute-deficient metals for energy and a number of important industries has been made. The authors express the opinion that the mineral resource base of uranium and rare earth elements in Russia can be significantly increased due to the presence of these critical metals in the dictyonema shales of the Baltic sedimentary basin, since only within the studied Kaibolovo- Gostilitsy prospecting area the largest uranium resources and large resources of rare earths have been discovered, which may increase even more with further geological research in the conditions of a developed infrastructure of the middle zone of the Russian Federation.

As a result of generalization of geophysical studies, petro-paleomagnetic and structural-geomorphological analyses, as well as thermodynamic modeling, some features of ore formation in the hydrothermal system of Cape Fiolent (southwestern Crimea) under island arc conditions were revealed.
It has been established that the main transformations of rocks of the Middle Jurassic igneous complex of Cape Fiolent occurred under the influence of hydrothermal fluids during the introduction of felsic intrusions during 168–140 Ma. The zones contain sulfide mineralization, the main minerals of which are pyrite, sphalerite, pyrrhotite, galena, chalcopyrite and arsenic pyrite. In the central parts of the hydrothermal alteration zone, massive sulfides are strongly weathered; these zones contain many secondary sulfates. In the marginal parts of hypergenic limonite, yellow-brown goethite prevails in the oxidation zone, yellow jarosite in the center, which is probably due to the large amount of pyrite in the center of the system, which gave more sulfuric acid during oxidation. The presence of native sulfur in the section testifies to the mixing of the acidified hydrothermal solution with seawater. Complex petro-paleomagnetic and magnetometric studies have shown that contact changes and transformation of the contrasting basalt-rhyolite formation occurred along the NNW-trending faults.

On the example of the Novo-Ursk tailing dump (Salair Ridge), the typomorphic characteristics of barite are considered. It was found that in the dumps, in addition to residual barite from pyrite-polymetallic ores, there are its authigenic varieties. Ore barite grains are found in the form of fragments of irregular shapes, less often grains of a tabular habit, have a dimension of 50–400 microns, Sr up to 1.41 wt.%. Newly formed barite occurs as single grains or clusters of round and elongated shapes or acicular crystals, ranging in size from 1–2 μm to larger aggregates that form veinlets or clusters in the siliceous matrix in association with jarosite and/or anhydrite. Among the impurities, Pb up to 6.33 wt.% was noted, less often Fe up to 0.73 wt.%, Sr up to 0.94 wt.%. It was shown by using thermodynamic modeling that the concentrations of Ba, SO4, Fe and Ca in solution vary within several orders of magnitude when the mineral composition of the tailings mound zones changes depending on the Eh–pH conditions of their formation. It has been suggested that the formation of barite along with pyrite may occur as a result of the action of a reductive biogeochemical barrier or a sulfate concentration barrier in the deeper parts of the section where supersaturation is achieved.The most informative typomorphic feature proving that barite was formed under tailings conditions is particle morphology, mineral association and chemical composition.

The lithologic-facial, mineralogical, petrographic, and lithogeochemical studies of Visean terrigenous sediments in the borehole section at the Bashkirian arch were carried out to clarify the sources of matter and sedimentation conditions. Terrigenous rocks of the Radayevsky and Bobrikovsky horizons are characterized by predominantly good sorting and pelletization of clastic material. A significant distance from the source of drifting is assumed. Terrigenous rocks of these horizons are sediments of the first and second sedimentation cycles. The rocks of the Tula horizon are characterized by average sorting and pelletization, which indicates the proximity of the drift source to the sedimentation basin. They are rocks of the first sedimentation cycle. The source of clastic material for the Radayevsky and Tula horizons was found to be rocks of acidic composition. For the beaver horizon, the acidic and the main source of drift was established. It is assumed that sedimentation of rocks occurred in coastal-marine conditions on the passive continental margin, with the inflow of clastic material from the inner parts of the East European Platform, due to overwashing of the early accumulated terrigenous rocks of the Devonian and Proterozoic, as well as destruction of the basement ledges, which were activated in the Early Visean time during the manifestation of folding. The presence of basic rocks in the Bobrikovsky horizon may indicate that the material came from the orogen.

The modern evolution of the dynamics of the structure of the hydrocarbon resource base in various regions is characterized, as a rule, by the gradual replacement of traditional sources with more complex ones. The latter are currently classified as hard-to-recover reserves (HTRR). The process of mastering and involvement in the development of HTRR is closely related to the transition to an innovative path of development, the creation of new technologies, the strengthening of the role of local knowledge, the accumulation of experience working with non-trivial sources of raw materials, and most importantly, with the efforts cooperation of various participants involved both in scientific and technological processes and in the development of subsurface areas. All of the above is impossible without the formation of an appropriate institutional framework with regional specifics. One example of an approach implemented in this area is the Canadian province - Alberta. There is also some experience in this field in Russia – in the Republic of Tatarstan. In a comparison with the initial conditions and approaches to the development of hard-to-recover hydrocarbon resources in these territories shows that there are both common and distinct features within the framework of the implemented approaches. Consideration of the latter is important from the point of view of choosing the directions for the formation a domestic working model in this area.

The purpose of the work is to identify the composition of the initial reservoir hydrocarbon (HC) system of the Bazhenov formation, as well as to assess the influence of the presence of a heavy solid hydrocarbon phase (bitumen) in the formation on the production of mobile fluids using PVT modeling methods. The article describes the necessary experiments to determine the component composition of the C81+ fraction and the PVT properties of the formation mobile fluid taken from the well and the bitumen extract from the rock, and also presents their results. In addition, the properties of fractions up to C81+ were calculated depending on the molecular weight for PVT modeling (extension of the Katz-Firuzabadi table). One of the important parts of the article is the assessment of the ratio of bound and free oil in the original reservoir system. Based on geochemical research data, an analysis was performed to assess the component composition of the original system (using the example of the Bazhenov Formation) using rock pyrolysis and studying formation fluid and bitumen. Using the results of studies of reservoir fluid samples, a PVT model was built and tuned. This PVT model was used to assess the properties of the initial reservoir hydrocarbon system and was adjusted to the fraction of the solid phase in the reservoir at the initial reservoir conditions. After this, based on the PVT model, an assessment was made of the influence of the presence of a solid phase in the composition of the reservoir system on the behavior of a mobile hydrocarbon fluid during reservoir development for depletion, as well as on the use of enhanced oil recovery methods (injection of associated petroleum gas and thermal methods of influencing the reservoir).

The influence of core properties on the state of residual oil in the process of oil displacement by water at the micro level is investigated. The pore size distribution, core permeability, dynamics and morphology of residual oil were studied. The analysis of the available experimental approaches to the study of the properties of the core and residual oil in the core samples showed that the existing methods do not provide complete information about the studied parameters. To solve these problems, it is proposed to use a combination of innovative relaxation-diffusion spectroscopy technology of nuclear magnetic resonance with traditional technology. A combination of mercury injection and nuclear magnetic resonance is used to measure the pore size distribution. The core permeability was determined using the nuclear magnetic resonance method. Two-dimensional nuclear magnetic resonance spectroscopy makes it possible to study the microscopic state of residual oil in an undisturbed core during the displacement process. With the help of the proposed methodology, a core study of the Shengli deposit in China was carried out. Pore size distributions were obtained, permeability and residual oil saturation at different stages of displacement were studied. Four types of residual oil are distinguished: strip-shaped (island), film, mesh, continuous. The influence of permeability on the fraction content of different types of residual oil in the process of displacement is shown. The research results demonstrate the influence of the pore space structure and wettability on the state of residual oil.

The relevance of the development of a methodology for the operational assessment of the bottomhole formation zone (the permeability of the bottom-hole formation zone and the skin factor) is primarily due to economic considerations, since existing approaches to its definition based on hydrodynamic studies lead to shortages and increased risks of failure to ensure the output of the well. In this regard, the use of modern methods of working with big data, such as deep learning of artificial neural networks, will ensure monitoring of the condition of the bottom-hole zone of the well formation without stopping them for hydrodynamic tests, which will reduce losses for oil production enterprises. It will allow for operational analysis for effective and timely application of intensification technologies, enhanced oil recovery. The authors analyzed the existing methods for determining the bottom-hole characteristics of the formation and machine learning approaches in the direction of solving this problem. The article presents a methodology for the operational assessment of the state of the bottom-hole formation zone: the permeability of the near bottomhole zone (NBHZ) and the skin factor using artificial neural network training approaches based on geological, operational data and the results of interpretation of hydrodynamic studies on the example of sandstones of oil fields in the Perm Region. A fully connected neural network was used to predict the NBHZ permeability. The article presents the results of testing various neural network architectures: the number of layers and neurons in layers with the choice of the best one. Some techniques were used to prevent over-training of models. The author’s methodology for assessing the skin factor of wells is proposed using a comprehensive analysis of the constructed statistical models and training models of artificial neural networks to solve the regression problem. In future studies, it is planned to use recurrent and convolutional neural networks to study the dynamic components of the formation of the bottom-hole formation zone and create an integrated approach to solve the problem.

The operation of oil production wells is accompanied by the invasion of well killing fluids into a near wellbore zone while well intervention which deteriorates rock permeability and decreases well oil rate. In order to restore the permeability of the rock in the near wellbore zone of the formation, it is proposed in this work to use ultrasonic alternating loading during well inflow stimulation. To study the effect of alternating loading on the permeability of rocks, a laboratory set-up is developed and filtration experiments are carried out. The rock studied was sandstone of medium permeability. The experimental studies included four stages: filtration of the killing fluid (calcium chloride solution) in the forward direction (simulating well killing); keeping the sample in conditions of pumped kill fluid; filtration of kerosene in the opposite direction (simulating an inflow stimulation) until the maximum possible restoration of permeability; filtration of kerosene in the reverse direction under ultrasonic alternating loading conditions for additional permeability restoration. It was revealed, that under conditions of ultrasonic alternating loading, the pore space of the rock, previously blocked by particles of the killing fluid, is unblocked and the permeability of the samples is restored. An analysis was made of the mechanism of blocking the pore space with the killing fluid and restoring the permeability of the rock.

The paper presents the results of experimental evaluation of oil displacement efficiency by flue gas of a thermal power plant, compared to water, for a carbonate reservoir in the Ural-Volga region. The experiments were performed under two different injection schemes using an original laboratory complex for coreflood studies, with recombined reservoir oil, model of formation water, reservoir core material, and under reservoir thermobaric conditions. It has been confirmed that due to the prevailing nitrogen content and low values of reservoir pressure and temperature, flue gas is ineffective as an independent displacement agent either for injection from the beginning of reservoir development or as a tertiary method after waterflooding. Taking into account the relevance of synergy between increasing oil recovery and sequestration of industrial emissions, evaluation of flue gas injection as part of water-gas mixtures (SWAG) is recommended.

Underground gas storages are an important component of reliable year-round operation of the country’s gas transportation system. The task of increasing the storage capacity is relevant both for newly created underground gas storages and for existing ones. The expansion of underground gas storage is a procedure for the sequential increase of gas volumes in the reservoir. It requires considerable time and in homogeneous formations can reach from eight to ten cycles of gas injection and production. During this period, the technological indicators of the development are stabilized, a stable transition zone is formed along the gas-water contact, and the active and buffer volumes of gas are stabilized. The main aim is in investigation of the influence of various factors on the formation of the transition zone within the gas-water contact during the creation and operation of underground gas storage in the elastic-water-pressure regime in fracture-pored reservoirs. Paper was based by Hydrodynamic computer 3D modelling. The nature of the influence of the following parameters on the volume of gas pushed into the aquifer region has been established: the angle of incidence of the formation, the values of minimum and maximum pressures in the gassaturated part during the operation of the underground gas storage, the permeability of the matrix (intergranular) and fractures permeability.

This research discusses issues related to hydrogen production, a promising source of “green” energy. Various methods of hydrogen production are considered, along with a new technology for hydrogen synthesis in natural gas reservoirs that has never been implemented before. At the same time, existing published experimental studies indicate a high probability of hydrogen synthesis when steam is injected into oil reservoirs. However, considering that oil is the primary raw material for hydrogen generation, there is high uncertainty about the success of the process in natural gas fields in the absence of residual oil. The experimental study presented in this work aims to justify the possibility of hydrogen synthesis under conditions of a natural gas reservoir. Specially designed reactors filled with different models of porous media, including the rock of a real gas field, are used for the physical modeling of the process. The process simulates injecting steam into a preheated porous medium mixed with hydrocarbon gas, specifically methane, at a reservoir pressure of 80 atm. The main variable parameters, aside from the type of porous medium, are the temperature and the steam-tomethane ratio in the system. The article presents the results of a series of nine experiments. The gas products were analyzed using a gas chromatograph. At the same time, the properties of rock samples were investigated after each experiment. The results of the experiments reveal patterns of concentration of hydrogen produced depending on the parameters, indicating the high potential of hydrogen synthesis technology under reservoir conditions in natural gas fields.