Introduction. Until relatively recently, all carbonate rocks have been divided into organogenic and chemogenic rocks. The former group includes those half-composed of skeletal remains, thus representing a biological problem. The group of chemogenic carbonate rocks initially included all carbonate rocks with a crystalline structure. Later, the “chemogenicity” of formation was attributed only to pelitomorphic and microgranular varieties, while pure crystalline structures were recognised as the result of secondary recrystallization.
However, the purely chemical precipitation of carbonate material from ocean waters by exceeding the solubility limit appears to be impossible. It occurs either biogenously during the formation of carbonate skeletons or biochemically as a result of changes in the acidity or alkalinity of the medium. The latter is typically implemented due to a carbonate disequilibrium between, on the one hand, the dissolved bicarbonates of calcium and magnesium and, on the other, water-dissolved carbon dioxide. The removal of the latter by photosynthetic organisms disturbs the dynamic balance and leads to an increased alkalinity and precipitation of carbonates, firstly calcium and then magnesium ones at higher pH values. Along with plants, microbial communities perform a similar function.
Aim. The paper presents the results of generalization and systematization of accumulated research data on the abovementioned forms.
Materials and methods. In addition to literature materials, carbonate rocks of various ages — from the Vendian and Lower Cambrian of the Siberian platform to the Crimea Neogene and sediments of contemporary oceans — were examined using macro- and microscopic (mainly) methods of studying and describing specific objects.
Results. Сoccoid, tubular and fibrous formations, i.e. particular bacterial “skeletons”, represent one precipitation form. At the same time, bacterial communities produce glycocalyx, representing an extracellular polymer substance, which forms a basis for submicroscopic precipitates of carbonate minerals. In this case, specific sheet- and plate-like carbonate material precipitates can be formed. The environments for implementing such mechanisms are highly diverse. Microbiolites can be formed in water bodies, including from fresh to substantially and even abnormally saline waters, in suspended matter and at the bottom of basins, both at the stage of sedimentation and during further diagenetic processes. The most famous example of the latter are various nodules.
Conclusions. The processes of sediment formation and material deposition are somewhat different. The formation of a solid phase is determined by the biochemical activity of microbiota and, first of all, the creation of geochemical conditions that contribute to the appearance of a solid carbonate material. However, the fixation of this material in a sediment is implemented either in “skeletal” ball-shaped (coccolites) and tubular (tubiphytes) forms, or by precipitation as a result of absorption on glycocalyx, or by the formation of various — both isolated individual (thrombolite microclusters, oolites and oncolites) and laminar (stromatolites) — forms.

Introduction. The 60 m wide quartz dolerite stock, opened by a quarry, is heavily alternated by secondary processes, which makes it difficult to study.
Aim. Reconstruction of primary magmatic structures and determination of conditions conductive to their crystallization and late alterations.
Materials and methods. In order to assess the conditions of magmatic crystallization and massive late alterations, thin sections of selected samples were studied and chemical analysis of rocks was performed.
Results. The stock was established to have a primary double structure with a wide centre and a narrow annular border (1 m). This is due to the contraction and reintroduction of a melt along the edge of the stock. The melt inside the ring is adiabatically heated to 1175° and the water pressure drops to 0.5 kbar, as compared to the centre (900° and 2 kbar). Therefore, the centre and edge have a different primary composition with plagioclase (An50), qartz, magnetite and glass (5%) in the centre and early plagioclase, quartz, pyroxene, plagioclase microlites, miarolitic cavities and glass (30–40%) at the border. Final hardening and new contraction lead to the formation of radial cracks in the ring. The mechanical work, spent on their formation, sharply reduces the level of internal energy, while the expansion of cracks leads both to adiabatic cooling of the solution in the border zone of the stock and massive low-temperature metasomatosis (260–132°C). The reactions proceed diffusionally when the solution is stagnant with the massive formation of pseudomorphoses. Due to a decrease in the volume of reacting solid phases and an increase in the total porosity under the conditions of dominant decompression, part of the silica is removed upwards. The centre is cooled slowly with the preservation of relics and their successive alteration from acid to alkaline ones. Initial acid reactions are provided by the complete dissociation of a weak carbonic acid, followed by strong acid and final alkaline reactions provided by chlorine and incomplete dissociation of carbonic acid, respectively.

Background. One of the key approaches to reducing the long-term effects of global warming consists in capturing, transporting and disposing and/or burial of carbon dioxide. The Russian Federation is one of the leaders in carbon dioxide emissions. At the same time, having great potential in the field of CO₂ burial in the subsoil, there are currently no industrial projects for capturing, transporting and utilizing and (or) storing CO₂.
Aim. To study of the retention mechanisms and burial features of carbon dioxide within various geological formations.
Materials and methods. Based on the analysis of extensive material, a review of existing options for the utilization and storage of carbon dioxide in the bowels has been prepared.
Results. Burial assumes CO₂ injection into rock layers, which are capable of its absorption and safe long-term retention. Various options for the burial of carbon dioxide in the Earth interior are considered. The main ones are layers of depleted hydrocarbon deposits and mineralized aquifers. Also, carbon dioxide storage can be carried out in undeveloped coal seams, saline and basalt formations. The basic mechanisms of retention, necessary geological conditions and characteristics of potential reservoirs are described. The risks and uncertainties of burial in various geological formations are analyzed. Examples of the world’s most significant projects for the utilization and disposal of CO₂ in the Earth interior are given. Such as Sleipner in Norway, In-Salah in Algeria, etc. It is indicated that the potential of Russia in the field of utilization and (or) disposal of carbon dioxide in the bowels is quite high, but it has not been fully assessed.
Conclusion. At present, the most studied and tested options for the utilization and storage of carbon dioxide in the Earth interior are as follows: the use of carbon dioxide as an agent in the methods of enhanced oil recovery, the storage of CO₂ in the strata of depleted deposits of hydrocarbon raw materials and in mineralized aquifers.
It is necessary to concentrate efforts on a purposeful geological study of various conditions for storing carbon dioxide in the Russian Earth interior, as well as on the development of uniform requirements for the geological parameters of CO₂ underground storage facilities.

Introduction. In order to characterize the oil and gas potential of any area under exploration, its structural and tectonic evolution should be studied. In this paper, a structural and tectonic modelling of the Bering Sea is carried out.
Aim. To identify the structural and tectonic characteristics of the Bering Sea by interpreting the results obtained during a geodynamic analysis of sedimentary basin formation, based on the tectonic and geodynamic paleoreconstructions and sedimentary basin modelling of the Bering Sea.
Materials and methods. A structural and tectonic modelling of the Bering Sea sedimentary basins was carried out using contemporary methods of basin analysis and numerical geological modelling (PetroMod software, Schlumberger). Three-dimensional time-spatial structural-tectonic models of the Bering Sea were formed using the bottom structural maps of Pliocene-Quaternary deposits, near the Lower Miocene and Oligocene tops and along the acoustic basement bottom. Maps were digitalized and converted to grids (with a 500-m step), in which the discrepancies (intersections) were removed taking into account the available geological and geophysical data (seismogeological sections). The contemporary surface of sedimentary basins was constructed by the connection of bathymetric and topographic maps. The beginning and end time of sedimentary accumulation periods was determined in accordance with the international stratigraphic scale.
Results. The performed study identified the sufficiently continuous development areas of the oceanic or suboceanic crust of deep-water (back-arc) basins, aged from the Upper Jurassic-Cretaceous to the Cenozoic and repeatedly affected by the subsequent phases of the tectonic and magmatic activation; development belts of the Cretaceous-Cenozoic block-magmatic basement of island arcs, locally including reformed basement blocks of an older, Paleozoic or Cimmerian, consolidation; extensive depth-differentiated alpine/newest (syn-oceanic) shelf platforms, occassionally partially destroyed due to the latest destruction, including blocks or large blocks of Pre-Cambrian or Paleozoic relatively rigid massifs in the structure of their base.
Conclusion. The modelling results indicate the deeply submerged West Anadyr, East Anadyr and Central Anadyr basins to be possible depocentres with their own hydrocarbon generation centres.

Introduction. The conditions of formation and distribution of accumulations of traps and deposits in the Caspian region are considered.
Goal. Assessment of conditions for the formation and distribution of traps and deposits in the Caspian region.
Materials and methods. Statistical generalization and systematization of data and materials partially borrowed from reference literature, stock sources, field data and published works [2, 5, 7].
Results. As a result, mainly in platform shelf conditions and in local areas of relative stabilization or weak oscillatory movements, the formation of lithological-stratigraphic and combined traps can be associated with a variety of accumulative and erosive-accumulative forms of coastal and isolated shallow waters remote from the coast. Finally, separate groups of traps are formed during periods of relative geodynamic stabilization, in water areas where conditions for carbonation accumulation and the formation of biogenic structures are provided.

Background. During the drilling process, all wells undergo distortion to a greater or lesser extent. In a number of cases, the distortion of wells causes no significant effect on the results of drilling. Therefore, the actual position of the well shaft and bottom coordinates are not determined. This applies to mapping, engineering-geological, blasting and other wells having a shallow depth. During deep-well drilling, especially at the final exploration stages, issues of drilling wells according to design trajectories acquire a greater importance and significant resources for their solution. The application of technical means for changing the direction of the well (whipstocks) is associated with a number of problems related to tripping operations.
Aim. To reduce the time input needed for adjusting drilling trajectories by excluding tripping operations when conducting controlled drilling works.
Materials and methods. The operating principles of various types of deflectors were studied. The results of investigating deflectors of continuous action are presented, along with means for adjusting drilling trajectories and optimizing the time required for controlled drilling works.
Results. The conducted analysis revealed the direct proportion between the time spent on tripping operations and the costs incurred in controlled drilling.
Conclusion. In order to reduce the time input needed for tripping operations during drilling, technological means should be developed to exclude them from the entire process.

Introduction. Torsional vibrations caused by drilling using a polycrystalline diamond compact (PDC) bit are analysed using wellbore data obtained under various drilling modes. The drilling caused by torsional vibrations are analysed. Two types of torsional vibrations, including those caused by the cutting action of a bit and by frictional forces.
Aim. To investigate the induction of torsional vibrations as a result of rock destruction by PDC bits.
Materials and methods. The research methodology was based on “Richard-Germay-Detournay” and “Tian-Detournay” bit designs and methods for reducing the critical effects of torsional vibrations induced by PDC bits during rock destruction.
Results. Statistical analysis has shown that the drilling efficiency of the bit (DE) correlates well with the occurrence of torsion vibrations caused by the bit. The aggressiveness of the cutting structure of the PDC bit can be represented by an average DE rating. If the PDC bit is designed so that its DE exceeds a critical value, then the occurrence of torsion vibrations on the bit is unlikely during drilling.
Conclusion. When drilling with a polycrystalline diamond PCD bit, two types of vibrations occur. If torsional vibration occurs due to the cutting action of the bit, then the fight against this process is focused on the design of the bit and operational parameters, the load on the bit and the speed of rotation of the bit. If the torsional vibration is caused by friction, vibration reduction methods should be focused on changing the design of the BHA and the drill string or the profile of the well. Therefore, it is very important to determine whether the torsional vibration is caused by the friction force of the elements, the cutting action of the bit, or both. In drilling, it is always necessary to search for the maximum penetration speed by changing the load on the bit under specified drilling conditions. To do this, it is necessary to evaluate the drilling efficiency of the DE bit, therefore, this article has evaluated the parameter depending on the size of the bit, which will determine the critical value of the drilling efficiency parameter.