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The paper presents results of the experimental study of geochemical processes in the “formation water – CO – rock” system at reservoir conditions for waterand oil-saturated intervals of several typical terrigenous and carbonate formations of Urals-Volga region. Compositions of formation water and dissolved gas are analyzed at each stage of the experiments, as well as mineral composition of core samples before and after the interaction. Based on the experimental results, a summarizing analysis is presented of possible physical and chemical processes occurring in the “formation water – CO2– rock” system during carbon dioxide injection into waterand oil-bearing formations. The results of the experiments allow us to highlight the significant effects of dissolution and resuspension of carbonates and halite during exposure of carbonized formation water with core material of different lithology and saturation character. In a number of experiments, significant changes in the iron and sulfate anions content were recorded, indicating the interaction of the solution with pyrite and gypsum. There were no significant qualitative and quantitative differences in the results of experiments with core material from water-saturated and oilsaturated intervals of the same lithology.

The paper presents new thickness and sandiness maps of the Visean terrigenous strata (Radayevkian and Bobrikian regional stages, Lower Carboniferous) of the South Tatar Arch, constructed using the “Natural Neighbour” spatial interpolation method in ArcGIS Pro software based on the analysis of geophysical survey data for more than 30,000 boreholes.The interpretation of the maps in combination with the results of sedimentological, ichnotextural and petrophysical core studies, supplemented by the analysis of archival and published materials, provided an opportunity to update the approach to modelling the sedimentation of the terrigenous Lower Carboniferous of the South Tatar Arch. The proposed sedimentation models of terrigenous and coal-bearing sediments take into account the chronostratigraphic data, the karstification of isolated carbonate platforms, the sediment accumulation rates and the ichnotextural characteristics of the sediments. It is concluded that the accumulation and preservation of terrigenous and peat (coal-bearing) sediments differ in duration (0.1 million years vs. 1.5–2 million years) and are consequently associated with transgressive and regressive phases.The accumulation of terrigenous sediments includes: (a) transgressive eustatic episodes – short-term incursions of a marine basin onto the eroded surface of an isolated carbonate platform, during which silty and sandy, wellsorted bioturbated sediments were accumulated, often with a variety of ichnofossils of marine benthic organisms; (b) the regressive eustatic phase resulted in the predominant erosion of sediments on the arch; whereas sediments in the incisions were largely preserved.The accumulation of peat (coal-bearing) deposits includes (a) the regressive eustatic phase, during which the vast area of the eastern Volga-Urals region was covered with flourishing vegetation and stable swamp environments were forming in the incisions of the Tournaisian surface; (b) the transgressive phase – the peat was overlaid and buried by transgressive marine silt-sand sediments; then it was compacted and transformed into coal. The alternation of coal-bearing and transgressive intervals indicates the cyclicity of these processes.The proposed sedimentation models extend the concepts of previous studies and are consistent with the developed maps of thickness and sandiness of the Lower Carboniferous terrigenous sediments, explaining the complex, covering and mosaic distribution of sand bodies over the area, as well as the filling of incisions with sediments of different lithological types.

The article provides an overview of ionmodified waterflooding technology, also known as low salinity, controlled salinity, or Smart water. This technology is currently considered one of the most promising approaches in the development of oil deposits in carbonate reservoirs due to its economic efficiency and environmental safety.The article discusses the main mechanisms and processes underlying ion-modified waterflooding and presents the results of laboratory studies conducted on core samples from foreign oil deposits. It includes an analysis of several studies, including contact angle measurements and core flooding experiments on core samples from oil deposits in carbonate reservoirs on the eastern side of the Melekess depression in the Republic of Tatarstan.It is important to note that the Vereyian deposits explored in this article are not a typical example of test objects for ion-modified water injection. This is because they are characterized by a low reservoir temperature of 23 °C, which suggests that the efficiency of the technology would likely be lower compared to studies conducted abroad, where reservoir temperatures were significantly higher. For example, Darvish Sarvestani et al. studied reservoir conditions at 90 °C, Yousef et al. – reservoir temperature of 100 °C, and Austad et al. examined the Ekofisk field at 130 °C and the Volhall field at 90 °C in Norway.However, as several studies have indicated, prolonged contact between rock samples and ion-modified water contributes to significant hydrophilization of the rock surface, as confirmed by contact angle measurements. The contact angle decreases from approximately 138.3° to 53.45° after exposure to ion-modified water.Additionally, the core flooding experiment demonstrated a slight increase in the oil displacement coefficient, reaching 9.2%.These findings suggest the potential for enhanced oil recovery by injecting Smart water into the Vereyian sediments, although further research is required to confirm the underlying mechanism.

Long-term phased development of a multi-layer field, including tens and hundreds of oil-bearing horizons and local deposits, combined with their vertical and horizontal separation, creates conditions for the formation of residual oil reserves. For the purpose of identifying and spatial localization of residual reserves, an algorithm for retrospective analysis was developed and applied on the example of the Upper and Lower Devonian terrigenous deposits of the Romashkinskoe oil field, which have been developed since 1952. The long history of geological study and development of oil-bearing formations of the Pashiysky D1 (layers g and e), Mullinsky D2, Ardatovsky D3, Vorobyevsky D4 and Biysky D5 horizons is analyzed according to the data of 2605 wells. It is proposed to single out 6 categories of formations and the reserves contained in them. Previously undeveloped formations composed of conditioned reservoirs are classified as category 1. Formations composed of more clayey and less permeable reservoirs are awarded with category 2. Category 3 includes previously developed formations, but left before reaching the limit of water cut, and category 4 – currently being developed intervals. The least promising are those that are stopped after reaching the maximum water cut (category 5), as well as wedged out, replaced by non-reservoirs or considered waterbearing (category 6) formations. Categories were mapped to identify, visualize and describe the main patterns in the distribution of residual reserves, which are established both in single wells and in bypassed oil that include a group of wells. The algorithm was tested on the corporate information base of historical data on geological exploration, research and development of the Abdrakhmanovskaya area of the Romashkinskoe oil field. Examples of experimental workover operations to include the identified residual reserves in the development are given.

This article is devoted to the review of one of the currently relevant methods of enhanced oil recovery – low-salinity waterflooding (LSW) – on the example of terrigenous Tulian, Bobrikovian and Devonian reservoirs of the Tatarstan Republic fields.The first part of review contains information about the key processes underlying this method, such as swelling and migration of clay particles and wettability alteration, as well as the mechanisms that explain these processes, which include cation exchange, multicomponent ion exchange, electric double layer expansion, etc. Their understanding, in turn, contributes to the identification of the main factors, the presence or absence of which at the field allows us to give a preliminary assessment of LSW application. There are main factors: the presence of clay particles, a significant content of Ca2+ and Mg2+ ions, as well as multivalent ions in formation water, low formation permeability, reduced oil viscosity, an increased content of acidic and especially basic components in oil and, as a result, a hydrophobic type of initial rock wettability.Then, examples of using the method in other fields are given and the results of laboratory studies, including the measurement of the contact angle, core flooding experiments, are briefly highlighted.A preliminary screening is carried out on the basis of geological and field data from several fields of Tatarstan Republic, candidate fields are identified and a preliminary conclusion about LSW application in this region is made. The positive factors for the reservoirs under consideration, identified at the preliminary screening stage, include low formation temperature, high salinity of formation water with a significant content of divalent cations and the potential to shift the pH level from the current slightly acidic level towards increased alkalinity, and an increased content of polar oil components. In addition, the reservoirs of the Tulian and Bobrikovian horizons are characterized by the presence of clay particles, and the Devonian reservoir are characterized by a reduced oil viscosity coupled with an increased oil base number.

The displacement efficiency and residual oil saturation are the most important characteristics determining the recoverable volumes of oil and the waterflooding efficiency. The main data about these parameters are provided by laboratory core studies. Specialized field tests make it possible to evaluate the same characteristics in-situ, directly on a well, thus excluding the influence of scale effect and impact of core sampling and preparation.This paper presents the results of a field study to evaluate the displacement efficiency and residual oil saturation on a well draining terrigenous Devonian formations on one of the areas of the Romashkinskoye field. The results are compared with generalized dependencies based on core data. Significant influence of the scale effect (the effect of sweep multiplicity) on the estimated parameter values was noted, which indicates the need to supplement laboratory experiments with specialized field studies.

The Pashyian Regional stage (horizon) is the main productive unit of the middle Devonian clastic succession of the South Tatar arch. This article presents, for the first time, maps of the lower and upper parts of the Pashyian, including data on sand-shale ratio, number of sand layers (reservoirs) and thickness, based on the analysis of logging data from 25,000 wells. The maps were created by spatial interpolation of Natural Neighbor and ArcGIS Pro software.The model of sedimentation of the Pashyian Regional stage reflects the interpretation of the plotted maps as well as the synthesis of the results of detailed core investigations (lithological, sedimentological, ichnotextural, petrophysical, etc.) and analysis of archive and published materials.The main points of the proposed model are as follows. The Pashyian sediments were formed in a marine basin, in an environment comparable to that of the middle shelf of modern seas – in an offshore zone dominated by current activity. The basin floor was a relatively flat plateau, on which sandy, silty and clay sediments were simultaneously accumulated. Sediments of all types accumulated during sea transgression. Sea regression caused erosion and destruction of the already formed sediments.Positive landforms of seabed relief, composed predominantly of sandy well-sorted material, comprised autochthonous underwater sand bars, formed by constant currents parallel to the bathymetric contour of the seabed. Underwater sand bars formed extensive systems nearly throughout the entire territory of the modern South Tatar arch. At the same time, allochthonous, poorly sorted, less mature sediments were formed in underwater troughs produced by transversal currents (directed from the shore towards the sea).The proposed model explains the consistent thickness of the Pashyian Regional stage, the mosaic distribution of sand bodies over the area, and the lens-like shape of the sand and siltstone reservoirs. The model can be extrapolated to other stratigraphic intervals of the Devonian clastic succession with similar sedimentological features.

At the late stage of field development, residual oil reserves undergo a significant change from mobile to sedentary and stationary. These reserves are mainly located in technogenically and production altered, watered layers and areas of deposits.Localization and development of such sources of hydrocarbons is an effective method of increasing the final oil recovery factor in mature fields, due to the presence of a readymade developed infrastructure for production, transportation and refining, as well as the availability of highly qualified personnel.This article considers an approach that allows, based on neural network algorithms, the estimation the volumes and localization of residual oil reserves in multi-layer deposits in combination with the analysis of geochemical studies of reservoir fluids. The use of machine learning algorithms allows a targeted approach to the development of residual reserves by automated selection of wellwork. This approach significantly reduces the manual labor of specialists for data processing and decision-making time.

Nowadays, oil fields on the territory of the Republic of Tatarstan are developed with application of systems for reservoir pressure maintenance, involving injection of large volumes of water into the formation. Efficiency of waterflooding depends on the quality of the injected agent, and, despite the use of various technologies of preparation and treatment of injected water, with the lapse of time critical matrix porosity and permeability inevitably decreases. In this work the main sources of injection wells critical matrix clogging are considered: mechanical impurities, oil products and scales formation, and the results of the component composition analysis of deposits from cluster pumping stations are given. Using the Oddo-Thomson methodology, it is revealed that injected water is prone to calcite and barite deposition at bottomhole conditions. Physicochemical and core-flooding study of several reagents for removing colmatants: acid compositions, hydrocarbon solvents and complexing agents were carried out and their optimal formulations were determined. The matrix treatment technology, including the sequential injection of compositions based on hydrochloric and mud acids, was substantiated. An algorithm for calculating the optimal reagent volume has been developed on the basis of research data on the mineralogical composition of mechanical impurities and ionic composition of injected water. Four types of matrix treatment technologies were determined for the conditions of injection wells at the Romashkinskoye oil field Devonian formation, taking into account the composition of colmatant, and acid treatment designs were developed.

Application of hydrogeochemical modeling using PHREEQC software to study interaction of formation water, carbon dioxide and reservoir rock minerals during CO2 injection for enhanced oil recovery or underground storage is discussed. Hydrogeochemical modeling is a powerful tool to evaluate the physicochemical processes occurring in the “gas phase – aqueous solution – solid phases” system depending on initial parameters such as temperature, pressure and reactant concentrations. The use of hydrogeochemical simulators provides a wide range of opportunities to analyze the processes of dissolution and precipitation of minerals, changes in the ionic composition and pH of the solution, which can affect the efficiency of CO2 injection, fluid flow, well and equipment operation. A step-by-step method for modeling interactions in the “formation water – CO2 – rock” system using the PHREEQC hydrogeochemical simulator provides good reproducing accuracy for the results of laboratory experiments and analysis of their correspondence to the processes occurring under different conditions. The obtained results are useful for optimization of oil and gas production processes involving carbon dioxide, planning and stability assessment of underground carbon dioxide storage facilities and other geological applications.

Results are discussed for evaluation of effectiveness of the cyclic geomechanical treatment (CGT) on a Tournaisian carbonate reservoir. Analysis of laboratory experiments performed according to a special program to assess permeability changes for Tournaisian samples under cyclic changes in pore pressure is presented. The main conclusion is the positive selectivity of the CGT: an increase in permeability is observed for samples saturated with hydrocarbons (kerosene) with connate water, and maximal effect is related to the tightest samples. For water-saturated samples, the permeability decreases after the CGT. Thus, the CGT improves the drainage conditions for tight oil-saturated intervals. It is also confirmed that the CGT reduces the fracturing pressure in carbonate reservoirs. Using flow simulations on detailed sector models taking into account the results of laboratory experiments, a possible increase in well productivity index after CGT with different amplitudes of pressure variation was estimated. Results of a pilot CGT study on a well operating a Tournaisian carbonate reservoir are presented, including the interpretation of production logging and well testing. The increase in the well productivity index is estimated at 44-49 % for liquid and at 21-26 % for oil, with a more uniform inflow profile after the treatment. The results of the field experiment confirm the conclusions about the mechanisms and features of the CGT obtained from laboratory studies and flow simulations.

Introduction. In 2020, most doctors were at the frontlines in the fight against the novel coronavirus infection (COVID-19). In the process of searching for effective etiotropic drugs, news came in that type I interferons had been successfully used for the treatment of COVID-19. Choosing the optimal COVID-19 treatment strategy is of pivotal importance for vulnerable populations such as children.Objective of the study. To show our own experience in providing medical care to children with COVID-19 and present the results of a comparative study of the efficacy and safety of interferon alfa-2b drugs combined with highly active antioxidants in the complex COVID-19 therapy in children.Materials and methods. A comparative study of the efficacy and safety of interferon alfa-2b drugs combined with highly active antioxidants in the complex COVID-19 therapy in children was conducted. The study included children with a laboratoryconfirmed diagnosis of COVID-19 aged 1 – 17 years (n = 85). In the treatment group (n = 45), children received interferon alfa-2b drugs such as VIFERON® rectal suppositories and VIFERON® gel for topical administration according to the dosage regimen and standard therapy. In the control group (n = 40), children only received standard therapy in accordance with the recommendations of the Ministry of Health of Russia.Results and discussion. 3,696 patients, including 3,507 children, received medical care in the City Children’s Hospital No. 1 in Kazan since April 2020. The share of laboratory-confirmed COVID-19 cases among admitted children was 21% (n = 736), of which 85 were enrolled in the study to assess the efficacy of complex therapy with interferon alpha-2b drugs combined with highly active antioxidants. The interferon alfa-2b therapy of COVID-19 children reduced the duration of the key clinical symptoms of the disease by 1.5-4 days and the virus elimination time by 6 days.Conclusions. The use of interferon alfa-2b VIFERON® rectal suppositories and VIFERON® gel for topical administration according to the dose regimen in combination with the standard therapy in COVID-19 children contributed to faster elimination of clinical symptoms of the disease and virus elimination compared to the standard therapy.

Gas component study is one of the important tasks of petroleum geology. Gas component can exist in various forms in sedimentary rocks. Of great interest is nitrogen, the gaseous accumulations of which are formed in oil-bearing strata, causing complications during the oilfield development. The problem of abnormal nitrogen accumulations had great relevance in the fields of the Volga-Ural petroleum province, which is one of the long-term developed with a large stock of wells for various purposes. This article discusses possible sources of gaseous nitrogen and the reasons for its accumulations in oil-bearing reservoirs. The main purpose of the article is to clarify the reasons for the gaseous nitrogen and its deposits formation. The main patterns of the areal distribution of nitrogen gas accumulations in oil-bearing strata are revealed on the basis of field, hydrogeological, geological and geophysical researches data analysis. It has been established that during the gas caps formation, the source of gaseous nitrogen is its dissolved compounds in groundwater and oil, biochemical decomposition of which leads to the dissolved molecular nitrogen accumulation in a liquid medium. The release of free gaseous nitrogen and the formation of its accumulations is associated with the decompression of formation waters for natural (geological) or man-made reasons (hydrocarbons extraction). Disturbance of the natural hydrodynamic regime in oil-bearing formations leads to the release of gaseous nitrogen and the formation of its accumulations under favorable conditions (the presence of reservoirs, structures and impermeable rocks in the top of the formation).

In the process of oil reserves’ development, the in-situ stresses change. Knowledge of rock failure constraints will allow prediction of behavior of rock when subject to subsurface stress change. In this study, we used the results of studies of the Pashiyan sandstone core samples recovered from the Tashliyarskaya area well No. 14403. Six sets of samples, each consisting of three samples taken from the homogeneous intervals at the same depth, were used to determine the ultimate tensile strength, uniaxial and triaxial compressive strength in the in-situ conditions. An analysis of the methods for constructing a rock strength certificate, and comparison of the strength criteria described in State Standard 21153.8-88, the Mohr-Coulomb linear strength criterion and the non-linear Hoek-Brown criterion are provided. The Hoek-Brown criterion has the advantage of describing a non-linear increase in strength with an increase in overburden pressure and more adequately reflects the properties of rock. For the first time, a comparison of applicability of strength criteria obtained by different methods and based on the laboratory core analysis was made to determine their practical applicability. Comprehensive studies of the strength characteristics have never been previously conducted, and the results obtained will serve as the basis for further analysis and application in order to improve the development of the terrigenous Devonian Romashkinskoe field.

The probiotic properties of the Bacillus subtilis GM2 and GM5 strains were studied on 90 Cobb 500 broiler chickens aged one day that were randomly divided into three groups: the control group with the standard diet and two experimental groups (30 chickens per group) with the diet supplemented with B. subtilis GM2 (group 1) and GM5 (group 2) spores. The addition of B. subtilis GM2 and GM5 spores at a concentration of 1·107 CFU/g to the ration of broiler chickens improved their growth rate, as well as increased the digestibility of nutrients and modulated the intestinal microflora in them. The use of probiotics stimulated an increase in the live weight of chickens by 6.30% and 13.78% (p = 0.05) as compared with the control group. The average daily weight gain in experimental groups 1 and 2 amounted to 52.82 ± 0.36 g and 56.54 ± 0.47 g per chicken, which is more than in the control group (49.69 ± 0.40 g) – by 6.30% and 13.79% (p = 0.05), respectively. The administration of probiotics by feeding favored an increase in the population of lactic acid bacteria in the small and large (to a lesser extent) intestine – bacteria belonging to the Enterobacteriaceae, Lactobacillaceae, and Clostridiaceae families were isolated from the intestinal contents and identified. The veterinary-sanitary examination found that the meat of broiler chickens from the experimental groups meets all the GOST requirements for organoleptic, physico-chemical, and bacterioscopic characteristics. Thus, probiotics based on the B. subtilis GM2 and GM5 strains have a positive effect on the growth and fodder digestibility of broiler chickens.

Here we present the morphological and physiological properties of isolated Lysinibacillus fusiformis strain GM, its draft genome sequence as well as annotation and analysis of its genome. Initial analysis of MALDI-TOF mass spectrometry, 16S rRNA gene analysis and in silico DNA-DNA hybridization revealed that the strain belongs to the species Lysinibacillus fusiformis. The 4,678,122 bp draft genome consist of 17 scaffolds encoding 4588 proteins and 137 RNAs. Annotation of the genome sequence revealed cellulase and protease encoding genes, genes of adhesion proteins and putative genes responsible for the biosynthesis of antimicrobial metabolites. The Whole Genome Shotgun project has been deposited at DDBJ/EMBL/GenBank under the accession number NTMQ00000000.1 (https://www.ncbi.nlm.nih.gov/nuccore/NZ_NTMQ00000000.1). Keywords: Lysinibacillus fusiformis, Probiotic, Cellulase, Illumina MiSeq, In silico DNA-DNA hybridization

This work describes the development of microbial biopreparations – fodder enzymes and enzyme-probiotic complexes – for solving the relevant problems of industrial poultry farming. The characteristics of non-starch polysaccharides (NSP) of grain feeds have been discussed. The mechanisms of NSP antinutritive action, which interfere with the assimilation of nutrients and energy of grain feeds have been analyzed. The negative effect of NSP on intestinal microbiota has been shown. The mechanisms of positive effects of exogenous microbial NSP enzymes on both intestinal microbiota and assimilation of feeds have been investigated. The expediency of complex compositions containing NSP enzymes, amylases, and proteases has been proved. The anti-nutritive properties of phytates contained in poultry feeds and the expediency of using microbial phytases as fodder enzymes for poultry farming have been shown. The prospects of enzyme-probiotic complexes as an alternative to the use of antibiotics has been analyzed.

The studies show that when using the preparation "Degelm-14" after infection of birds, the histological structure in most of the studied organs was gradually restored. In the glandular stomach and small intestine on the 22nd day after application of the studied preparation the microstructure of the organ recovered completely. Microstructural changes in the cloacal pouch and spleen after application of Degelm-14 indicated restoration of the proliferative activity of the cells of the germinal centers. In the liver, at the final stage of the study, there were no signs of metabolic disorders in hepatocytes, and the dark pink coloration of their cytoplasm indicated an increase in synthetic processes in the cells of the organ parenchyma. But in the kidneys there were still observed signs of impaired glomerular filtration, regulating the function of the organ.