Introduction. One of the methods of forecasting oil-promising facilities is comprehensive studies of the core obtained during drilling. The emergence of new research methods, as well as the improvement of those already used, determines the need for further study of core material in order to obtain new data on the composition of rocks and their properties.

   Aim. A comprehensive analysis of the core taken from the wells of the old fund on the territory of the Southern structural region of the Pripyat Trough.

   Materials and methods. The work was performed based on the interpretation of data obtained as a result of a modern complex of works on primary sample preparation, lithological-sedimentological, mineralogical and pyrolytic studies of retrocore.

   Results. For the first time, the retrocore studies made it possible to form an conceptual lithological and sedimentological model of the formation of Upper Devonian (Yelets-Petrikov) deposits, determine the prospects of oil and gas potential for various types of reservoir rocks (terrigenous, carbonate, mixed), establish the boundaries of their distribution in the section and localize the main potentially promising objects for the search for hydrocarbons.

   Conclusion. Additional study and research of retrocore in a number of promising areas can provide important information about the true prospects of the oil-bearing capacity of the object. This is evidenced by the results obtained within the least studied Southern structural region of the Pripyat Trough. Despite the long-term storage of the core (for 30–50 years), fundamentally new data were obtained on the genesis of deposits, features of the mineral composition, hydrocarbon and generation potential. In addition, the study of the retrocore made it possible to form fundamentally new methodological approaches to the eff ective use of "retrodata" for the successful implementation of geological exploration tasks.

   Introduction. In recent years, oil & gas exploration process focus has shift ed towards clarifying the geological structure & resource potential of complex reservoirs. An example of these object types is Tyumen formation characterized by weak consistency, as well as a high heterogeneity and contrast properties.

   Aim. The aim is to develop an experimental approach of the resource potential probabilistic assessment of channel geobodies, considering the conceptual features.

   Materials and methods. This paper describes a methodology for estimating effective thicknesses based on a comprehensive analysis of G&G data with an emphasis on the bodies’ spatial structure analysis, considering the conceptual structure diff erentiation.

   Results. Multivariate calculation of effective thickness maps was performed in accordance with the developed methodology for considering the channel bodies’ diff erentiation. The results obtained were also compared with the assessment of effective channel thicknesses by morphometric analysis, and a high convergence of forecast values was noted using two different methods.

   Conclusion. Considering facies zoning with the involvement of sedimentation slices detailed analysis in the assessment process allowed us to obtain a correct eff ective volume forecast, in order to accurately plan perspective appraisal drilling.

   Introduction. A significant number of faults having various amplitude and rank within the Pur-Taz oil and gas region were recently detected. Basic principles of fault mapping make it possible to identify few of them, mainly more major in terms of amplitude and contrast; the main problem remains the identification of low-amplitude faults and faults without displacement. Therefore, fault detection algorithms need to be improved, which allow analyzing the spatial position of faults based on seismic attributes comprehensive analysis.

   Aim. The aim of the work is to clarify the geological & tectonic structure of the site under consideration, as well as the impact of identifi ed faults on development.

   For this purpose, the authors propose the use of complex attribute analysis as instrument of faults’ detection with various ranks.

   Materials and methods. The methodology of fault identifi cation based on the complex analysis of seismic attributes, emphasizing noise suppression and amplifying signals of faults. The workfl ow is based on the selection of the sequence of calculation of attributes. The developed methodology consists of three main stages — data preparation and noise suppression, faults’ borders highlighting, faults detection and quality control.

   Results. The optimal workfl ow of calculating attributes has been developed. Complex attribute analysis as a tool for identifying disjunctive disorders was applied at one of the fi elds within the Pur-Taz region. According to the results of the interpretation of tectonic disturbances in the work area, about 30 % of new faults were additionally identified. Moreover, the geometry of existing faults was clarifi ed.

   Conclusion. The authors propose the use of complex attribute analysis as a tool for identifying faults in order to localize structural and tectonic traps. Additionally, an analysis of the impact on the development of accounting for identified violations was carried out.

   Introduction. Oil recovery factor (ORF) is one of the key indicators of the oil field development. There are two main group of factors that infl uence ORF: is affected by two main group of factors: geological features of the oil field and technological parameters of its development. Currently, oil fields development requires an increasing volume of hard-to-recover reserves (HRR). HRR involved in the development are usually characterized by complex, low-power, low-permeability, highly dissected reservoirs. The cost of geological errors in the development of such oil fields increases. There are often additional negative factors. For example, low thickness of the clay barrier separating HRR from adjacent water-saturated layers. The main purpose of this article is to select the optimal system of the development with HRR separated by a thin clay barrier from the underlying water-filled layer.

   Purpose. The article proposes a strategy to develop АВ1(1-2) («Ryabchik») oil fi eld with HRR. Its development is complicated by the presence of the washed object AB1/3 with a thin fl uid seal between them. The purpose of selecting the optimal parameters of the development is to improve the well placement system. The selection of the optimal development system is carried out on a two-dimensional synthetic geological-hydrodynamic model.

   Materials and methods. The two-dimensional hydrodynamic simulator “NumEx2”, Gazprom neft company group own development, is used to solve the problem of selecting the optimal parameters of the development system and conducting a sensitivity analysis of the results.

   Results. An optimal development system is proposed in the conditions of HRR with an additional complicating factor in the form of an underlying washed formation. This development system is characterized by the following parameters: a row confi guration of longitudinally directed horizontal wells along the line of regional stress (340 degrees) with BPS (Burst port system) technology for conducting multi-stage hydraulic fracturing with a length of GU = 1200 m with a PSS = 28 ha/well (a = 1400 m, b = 200 m) with the formation of a reservoir pressure maintenance system in the form of a wellbore support system with hydraulic fracturing. The use of BPS technology for hydraulic fracturing reduces the starting water cut of the well by approximately 40 % and increases the half-length of hydraulic fracturing fractures by 90 m.

   Conclusion. A strategy is proposed for drilling a HRR object complicated by the presence of an underlying water-saturated layer separated by a thin clay barrier.

   Introduction. It is well known that early development of a gas cap results in migration and loss of oil from the oil rim. The process is poorly studied worldwide. Existing methods for estimation the degree of oil smearing for given reservoir properties and gas recovery efficiency are mainly applicable for underlying oil rims and overestimate the degree of oil smearing for marginal oil rims.

   Aim. The aim of the work is to develop a set of guidelines for carrying out analysis and development planning for the marginal oil rims during early development of a gas cap. A large gas condensate field located in Western Siberia is considered as a case study.

   Materials and methods. The paper introduces an approach for estimation of spatial distribution of oil reserves for marginal oil rims based on reservoir simulation which accounts both all available well surveys and conceptual geological model.

   Results. As a result of the case study a new approach for estimation the degree of oil smearing for reservoirs with marginal oil rims during early development of the gas cap is developed. Besides that, a set of guidelines for surveys design, analysis and accounting their results during development planning of oil rims are produced.

   Conclusion. Introduced approaches and guidelines for analysis and development planning for reservoirs with marginal oil rims allow to mitigate risks in estimation of production potential and develop optimal reservoir management strategy. Considered solutions can be applied to reservoirs with similar confi guration of fluids saturation.

   Introduction. Often, when developing Achimov (Ah) deposits, it is very difficult to achieve well productivity corresponding to the calculated indicators, due to the peculiarities of the geological structure of the deposit itself. One of the prerequisites for cost-eff ective operation is the almost universal hydraulic fracturing (FRACKING). Accordingly, there are difficulties in understanding the propagation of fracturing cracks; at what pressures cracks collapse occurs; what tonnage of proppant to use to obtain industrial inflow, while avoiding the unification of crack systems in the Achimov strata group.

   Aim. The aim of the work is to understand the behavior of field-geophysical (PGI) methods and their informativeness in analyzing the efficiency of hydraulic fracturing in Achimov deposits.

   Materials and methods. Examples of vertical wells (VS) with hydraulic fracturing and horizontal wells (GS) with multistage hydraulic fracturing (MGRP) are considered for analysis.

   Results. When considering the material, the data from the SUN studies show that cracks can have high half-lengths along the strike, which must be taken into account when modeling such objects, since as a result we can connect non-perforated thicknesses and the actual productivity will be higher than predicted. Also, according to the results of PGI in the sun, according to the technology considered in the article, it is possible to estimate the height of cracks. To select the most informative technology and complexes when planning research in GS, it is necessary to understand the longitudinal or transverse cracks created during hydraulic fracturing.

   Conclusions. Recommendations are given on the planning of research in GS with MGRP, taking into account the results of the VS, and ideas about the possible connection of bundles after hydraulic fracturing have also appeared. It is recommended to carry out the research approach considered in the article at all Ac facilities at the assessment stage, not only to understand the infl ow profi le, but also the propagation (assessment of height and connection between bundles) of fractures created by hydraulic fracturing. It is proposed, when conducting hydraulic fracturing in the Ac, to provide an up-to-date arrangement of the completion of the HS with separating packers and control valves to simplify the conduct of geological and technical measures (GTM).

   Objective. Determination of the minimum miscibility pressure, based on the results of physical modeling on a slim tube model, during oil displacement by gas for the conditions of Achimov deposits. Comparison of the efficiency of methane and associated petroleum gas as a displacement agent.

   Materials and methods. Recombination of reservoir oil was performed in two ways — combining all separator oil samples and further recombination, as well as combining reservoir oil samples (partially degassed) and further recombination. Preliminary estimation of the minimum miscibility pressure was performed based on analytical correlation and compositional (PVT — Pressure-Volume-Temperature) modeling. A set of physical modeling studies was performed using a slim tube model to determine the dynamics of displacement changes and chromatographs for further analysis of the released oil and gas. Filtration experiments were performed in accordance with the conditions of the Achimov deposits.

   Conclusion. By means of physical modeling on a slim tube model, the displacement coeffi cients for methane and associated petroleum gas (APG) injection have been determined. During analysis of the obtained results the dynamics of gas/oil ratio, pressure drop, component compositions of gas and oil during fi ltration experiments was evaluated. On the basis of the obtained data the displacement modes were determined, and the intervals of the minimum miscibility pressure (MMP) were calculated: 45.03 MPa — for APG; 45.89 MPa — for methane.

   Introduction. The existing approach to assessing the conductivity of a hydraulic fracture does not always clearly describe the actual operating data, especially for gas condensate fields. Possible reasons for this discrepancy are the lack of consideration of non-stationary effects arising during flow in the reservoir and insufficiently strict consideration of non-linear effects arising during flow in the fracture.

   Aim. Development of a methodology that allows assessing the conductivity of hydraulic fractures taking into account non-stationary and non-linear effects.

   Materials and methods. The work uses an analytical dimensionless model of flow in a hydraulic fracture developed by the author. The control parameters of the model are dimensionless conductivity and dimensionless D-factor.

   Results. The paper shows that the classical approach to describing the conductivity of a hydraulic fracture through the ratio of the conductivities of the formation and the fracture requires adjustment. It is proposed to take into account non-stationary effects arising during flow in the formation in the calculation of dimensionless conductivity, as well as to take into account the value of the dimensionless D-factor, the need for such adjustments is demonstrated. In addition, the paper shows that gas wells with hydraulic fractures can have a significant value of the D-factor associated with non-linear flow in the proppant package.

   Conclusion. The results of the work can be used in the design of the hydraulic fracturing process, in the design of field development using wells with hydraulic fracturing fractures, as well as in the selection of suitable methods for modeling hydraulic fracturing both in analytical models and in hydrodynamic simulators.

   Introduction. As conventional hydrocarbon reservoirs become depleted during extended production the industry is increasingly focusing on the development of hard-to-recover reserves. Key technologies for their exploitation include the construction of horizontal wells and hydraulic fracturing (including multistage hydraulic fracturing, MHF). However, in the case of thin reservoir formations where MHF is complicated due to high risks of fracture breakthrough into the gas-oil contact (GOC) or underlying water zone the construction of multilateral wells becomes more relevant. This approach increases the drainage area and raises well production rates to economically viable levels. In addition to maintaining the stability of the boreholes themselves the stability of the junction zone is a critical factor for the successful well construction.

   Aim. The objective of this study was to evaluate the junction zone stability in multilateral well’s horizontal open boreholes.

   Methods. The study employed complex 3D geomechanical modeling of the stress-strain state and rock stability in two boreholes junction zone under various sidetracking parameters: the orientation of the main borehole relative to horizontal stresses; the orientation of the lateral borehole relative to the main borehole (sidetracking direction and intensity); deviation angle of the main borehole; the influence of the lateral borehole’s diameter; different mud weight and corresponding wellbore pressures above and below reservoir pressure.

   Results. Geomechanical modeling combined with drilling geomechanics support and timely recommendations allowed to adjust the planned kick-off point when the current drill bit depth approached the junction zone. This optimization ensured safer intervals (in terms of stability) for both the bridge between the wellbores and the borehole wall. The accident-free drilling and the junction zone continuous stability during subsequent production confirmed the accuracy of the conducted analysis.

   Conclusion. Complex 3D modeling of junction zone stability accounting the results of 1D modeled mechanical properties, pressures and stresses allows to optimize lateral borehole sidetracking parameters during multilateral well construction. This approach ensures both accident-free well construction and its subsequent exploitation.

   Currently, one of the most pressing tasks in the oil and gas industry is the efficient production of hydrocarbons (HC) in fi elds with low values of filtration and capacitance properties (PPP). The key technologies in this approach include the construction of horizontal wells (HS) and hydraulic fracturing (HF), including multi-stage fracturing. The combined use of horizontal drilling and multi-stage hydraulic fracturing technologies is a successful solution in terms of net present value in the development of both conventional reserves and carbonated reservoirs with ultra-low permeability [1].

   Aim. Main aim of this work was to develop and test an approach that makes it possible to implement a unified algorithm for modeling a hydraulic fracturing fracture, constructing a design and redesign, as well as predicting the productivity of the fracture and ensuring the eff ective implementation of multi-stage hydraulic fracturing at the planning stage.

   Materials and methods. The proposed approach is based on comprehensive (geological, hydrodynamic, geomechanical) modeling, which is carried out using all data available for wells in the field, including geophysical survey data (GIS), results of core studies, drilling information, well design data, etc. For calibration of the elastic-strength characteristics of the rock, the results of core research are used, and the stress-deformed state of the geological environment is the result of 1D geomechanical modeling with calibration for special studies (stress test, injectivity test), injection tests and mini-fracturing, as well as drilling events.

   Results. The developed geomechanical approach was tested during the extraction of hydrocarbons from the Achimov deposits of one of the fields in Western Siberia. Five- and six-stage multi-stage hydraulic fracturing on horizontal wells was successfully carried out. The high accuracy of the predicted fracture parameters ensured the effective placement of the proppant in the fracture and the successful conduct of the main injection.

   Conclusion. Models built within the framework of the geomechanical approach increase the efficiency of retrospective analysis of hydraulic fracturing and are an indispensable tool for geomechanical support of hydraulic fracturing in real time. They have predictive power and are an effective tool that, after updating, can be used both at subsequent stages during multi-stage hydraulic fracturing and at other wells in the field.

   Background. During the construction of wells, casing strings are cemented. One of the goals of cementing is the qualitative separation of the layers, but in the process of construction, development, and operation of the well, the cement stone may collapse. Violation of the cement stone can lead to leaks in cement stones and the occurrence of sustained casing pressure (SCP).

   The aim of this article is to describe the developed methodology for laboratory testing of a domestic self-healing cement system (SHC) on a unique TS-400 stand, which allows simulating downhole conditions such as pressure and temperature, as well as evaluating the impact of casing pressurizing on the integrity of cement stone and the effect of differential pressure on cement stone. The ability of self-healing of a SHC system in contact with hydrocarbons in conditions close to borehole conditions was also evaluated.

   Materials and methods. The test procedure and methodology were developed by the authors of this article to ensure maximum approximation to downhole conditions and processes that ensure the impact on cement stone in the well in accordance with the conditions at the Bovanenkovskoye field. The tests were carried out on a unique TS-400 stand.

   Results. As a result of the tests, the properties of the SHC to self-healing cracks in cement stone under borehole conditions (pressure, temperature) were confi rmed. The procedure for the formation of a program of non-standard tests has been developed. The nature of cracks in the cement stone, depending on the standoff of the casing, is noted. The results of cementing wells with SHC at one of the fi elds of the Gazprom Neft GC are described.

   Conclusions. A method for testing cement stones in borehole conditions has been developed. Tests of the SHC were carried out under borehole conditions at the TS-400 stand. The ability of the SHC to self-heal cement stone in contact with hydrocarbons has been confi rmed. The effectiveness of the use of SHC in ensuring the well integrity in the field has been confi rmed.

   Introduction. Hydrocarbon field exploration and development require groundwater for well drilling, reservoir pressure maintenance systems, and production and technical needs during oil processing. In northern regions, the difficulties of prospecting, exploration, assessment of reserves, and exploitation of groundwater are associated with the diversity of permafrost distribution conditions and thickness, as well as the structural features of water-bearing strata.

   Aim. To determine criteria and develop approaches to predicting groundwater reservoirs in permafrost areas.

   Materials and methods. The study included generalization and analysis of geological and geophysical data on the structure of the upper 500 m of the sedimentary cover, including drilling data and geophysical well-log surveys, and the results of area electromagnetic exploration with shallow transient electromagnetic sounding in the near zone (TEM).

   Results. The paper describes approach to data integration for groundwater exploration within the permafrost areas of the Lena-Vilyui artesian basin of the Republic of Sakha (Yakutia).

   Conclusion. A comprehensive analysis and integration of geological and geophysical data using electromagnetic TEM data in Yakutia made it possible to study the structural features of permafrost rocks, the distribution of interpermafrost and subpermafrost groundwater reservoirs, and to derive approach to groundwater reservoirs exploration for various permafrost and talik distribution conditions.

   Introduction. The participation of biocenoses in the formation of various minerals has been studied and proved for quite a long time. But in some cases their role in the formation of sedimentary strata is not obvious. For example, the formation of secondary minerals in bottom-hole parts of wells at underground gas storages remained unstudied for a long time. In a number of wells such minerals had a strong negative influence on filtration-capacity properties of rocks and structural parts of wells.

   Aim. In order to optimize well operation and to understand the process of mineral formation by bacterial pathway, newly formed minerals and rock matrix of bottomhole zones of underground gas storage wells were studied.

   Materials and methods. To study the mineral and bacterial composition of the rocks we carried out studies on scanning electron microscope, optical microscope, diffractometer, as well as various optical studies.

   Results. The groups of newly formed minerals were revealed and their genesis was determined; bacterial biocenoses played the greatest role in the formation of such minerals.

   Conclusion. The volume and properties of filtration-capacity space of UGS reservoir rocks are largely determined by a wide complex of geological, biogenic, bio-chemogenic and technological factors.

   Introduction. The study of the core by mathematical modeling of filtration processes at the level of the void space of the rock has a number of significant advantages relative to traditional laboratory studies. However, there is no
common understanding of how the Digital Core technology can be effectively integrated into practical activities to support the development of hydrocarbon deposits.

   Aim. The purpose of the research is to provide the concept of applying the results of digital core analysis in the practice of reservoir modeling based on the existing experience in using this technology and original developments.

   Materials and methods. The rationale for the concept is based on the most signifi cant third-party and proprietary examples of the use of Digital Core technology to create a petrophysical basis and build a hydrodynamic model.

   Results. Using the Digital Core technology, based on the original semi-empirical core model and hydrodynamic modeling of the facies structure, the problem of taking into account the large-scale effect during the transition from one level of rock to another is solved for one of the sections of the Rosneft oilfield, where pilot works are carried out to displace oil with water and polymer solution. Calculations of relative phase permeabilities in the oil-water and oil-polymer solution systems have been performed. It is shown that the use of the results of digital core studies makes it possible to increase the adequacy of hydrodynamic modeling and thereby reduce the uncertainty of predictive modeling.

   Conclusions. Described the place of applying the results of digital core research in the process of modeling the development of hydrocarbon reservoirs and shown, that it makes this process more logical and more meaningful.

   Introduction. Machine learning is increasingly being applied in various industries, including the oil and gas sector. However, the quality of data collected from oilfi elds does not always allow for its correct use in the digitalization of production processes. Unfortunately, it is not possible to quickly re-equip all oilfields for more accurate and frequent data collection. As a result, we must continue working with the data that has already been collected.

   Objective. The objective of this work is to examine the set of transformations that occur with data in the process of its use in machine learning as a unified process (the ETL process).

   Materials and methods. As examples to demonstrate the discussed challenges and approaches, we used data on oil well operations. Python scripts were developed for data analysis and visualization.

   Results. The study found that the quality of data collected from oilfi elds is not always suffi cient for use in machine learning. To improve data quality during collection and preparation stages, it is proposed to implement ETL processes.

   Conclusion. The application of ETL processes will significantly increase the quantity and quality of data available for creating digital twins of oilfields. Therefore, the impact of introducing this technology is difficult to overestimate.

   Introduction. Thanks to the automation of various development processes, the economic efficiency of extraction in depleted fi elds is increasing. Infill drilling is one of the key activities for enhancing oil recovery in the later stages. Modern approaches to locating new drilling zones, optimizing well placement and economically evaluating of initial production increasingly use machine learning, big data analytics and digital twins.

   Aim. The objective of this article is to conduct a literature review on the latest approaches to infill drilling and highlight the most effective methods for automating the search for well candidates in large fields with limited datasets.

   Materials and methods. Modern approaches to identifying new zones for infill drilling were explored, including the generation of probability maps and the use of machine learning for data analysis. Additionally, automatic interpretation techniques of geophysical data to identify missed intervals of reservoirs was reviewed. Methods for well placement optimization were described, taking into account geological risks and economic factors. It was noted that the complexities and risks associated with infill drilling in mature fields stress the need to balance accuracy and timeliness of methods for effective decision-making.

   Results. The most effective and universal approaches for each stage of planning infill drilling were highlighted. The main stages include generating probability maps, well placement optimization and forecasting production parameters using analytical methods and machine learning.

   Conclusions. Modern approaches to automating infill drilling, which include machine learning and integration of various models, significantly increase the efficiency and accuracy of planning. These methods require further research to adapt to different field development conditions.