Oil Saturation In Reservoir Research Articles

Simulation of the thermal field in reservoir during the filtration of live oil and water with considering the heat of oil degassing and thermodynamic effects

In the process of water invasion of reservoir under conditions of pressure decrease below the bubble point pressure of oil with dissolved gas, when oil degasses, an area of three-phase flow of oil, water and gas appears in the reservoir. In this case, each of the phases makes a certain contribution to the formation of the thermal field in the reservoir, due to the thermodynamic effects shows and the heat of oil degassing. The thermal field forming is influence many parameters, for example, the initial water cut of formation, gas oil ratio, the ratio of reservoir pressure and bubble point pressure of oil with dissolved gas, the ratio of reservoir pressure and bottomhole pressure, etc. The thermohydrodynamic processes occurring in this case carry information about the formation and the near wellbore zone. One of the directions for using the features of the formation of the temperature field in this case is the use of thermometric studies of wells to diagnose the condition of the well and formation. Reservoir water invasion under the condition of oil degassing leads to a change in the temperature distribution in the formation, which can be used in diagnosing the identifying sources of water invasion. Using a numerical method for solving the equations of mass conservation and heat influx during non-isothermal three-phase filtration, in this work are studied the features of the formation of the temperature field in an oil-saturated reservoir with an initial water cut during oil degassing. As a result of calculations for various ratios of the initial water cut of the formation and the gas oil ratio, temperature dependences were obtained for different of well operation times. The obtained dependences of temperature on water cut and gas oil ratio can be used as palettes for quantitative evaluation of water inflow rates from formations.

Charging dynamic, resistance and accumulation process of tight sandstone oil of the paleogene Es3 member in linnan sag, jiyang depression

The study of the coupling relationship between the dynamic and resistance of oil charging is the key to revealing the process of tight oil accumulation. The Paleogene Es3 member of Linnan sag, Jiyang Depression was taken as an example, basin simulation, fluid inclusion analysis, and porosity inversion were comprehensively utilized to recovery the residual fluid pressure and charging resistance during the critical oil accumulation periods. Combined with the physical modeling of tight oil charging, the charging process and characteristics of tight oil under dynamic and resistance coupling were reproduced and the effects of dynamic and resistance on the oiliness of tight reservoirs were analyzed. The comprehensive analysis indicates that there were early and late periods of oil accumulation in early Dongying period and late Guantao-Quaternary period. The reservoirs had not been densified during the early oil accumulation period. The residual pressure of the formation was between 1.0–4.4 MPa and the reservoir charging resistance was generally small, so that the dynamic was generally greater than the resistance. But the oil saturation of the reservoirs was low due to the small amount of hydrocarbon generation. During the late oil accumulation period, the source rocks entered the peak period of hydrocarbon generation and expulsion and the residual pressure of the formation was between 4.2–12.1 MPa. The reservoirs had been close to or completely densified. The dynamic, resistance and dynamic and resistance difference all increased significantly. Under the stronger dynamic, the oil saturation of reservoirs rapidly increased, ultimately achieving tight oil enrichment. The results of this study provide insights into the dynamic process of tight oil accumulation and the distribution of oil in tight reservoirs.

The use of branched horizontal wells at the Zhanazhol field to increase oil recovery

The research presents an analysis and experiment on horizontal wells of the Zhanazhol field, an analysis of the operation of horizontal wells is carried out. The analysis of the factors affecting the efficiency of oil production by horizontal wells is carried out, experimental and industrial methods of operation are proposed for further implementation of horizontal well technology. The design of the construction of branched horizontal wells has been carried out. The purpose of this work is to substantiate the feasibility of switching to fundamentally new development systems using horizontal wells to increase the flow rate of liquid hydrocarbons using the example of the Zhanazhol field. The results of pilot tests of drilling branched horizontal wells to increase oil recovery at the Zhanazhol field are summarized. At the Zhanazhol field, the maximum capacity of oil reservoirs reaches about 190 m. The average capacity of oil–saturated reservoirs is about 3 m. There are intervals of impermeable interlayers in the productive formation. The thickness of most impermeable layers varies within 5 m. An impenetrable layer with a thickness of about 10 m is spreading widely. This affects the nutrition and energy supplementation of oil reservoirs, resulting in a rapid decrease in oil production and reservoir pressure. For example, the average daily flow rate of oil with a 15 mm fitting is more than 150 tons, but the current flow rate of oil with a 7 mm fitting is 52 tons (horizontal well No. 2407). The technology of drilling branched horizontal wells in certain geological conditions allows: to obtain initial flow rates 10 times higher than the flow rates of conventional wells with an increase in the cost of drilling only 1.5 - 2 times; to ensure accumulated production over 10-15 years of operation 10 times higher at the cost of extracted oil 3-5 times lower than for neighboring conventional wells; to increase the total oil recovery from productive formations by 20-30 percent; to thin the well development grids.

Complex of hydrodynamic studies of wells and formations at the Uzen field

The effectiveness of monitoring the development process depends on the availability of complete and high-quality information about the hydrodynamic parameters of productive formations, reservoir reservoir properties, technical condition of wells, etc. The purpose of oil, petroleum gas and reservoir water research is to obtain comprehensive data on their properties and composition, which are within the productive horizons of deposits, as a rule, are fickle. Ignoring the heterogeneity of oil properties over the area of the deposit and the lack of control over changes in physico-chemical properties during the operation of the field can lead to serious errors in predicting the parameters of field development. One of the most important sources of information is hydrodynamic (field) studies of formations and wells. The advantage of hydrodynamic methods for increasing oil recovery is that they are relatively easy to implement and do not require large economic costs. At the Uzen field, the assessment of the initial productive and filtration characteristics of the formations was carried out on the basis of studies of steady-state filtration (MSS) performed during testing of oil-saturated reservoir intervals during exploration and at the initial stage of industrial development of the field when the deposit was operating under natural depletion mode. The article presents the results of a study by the method of steady-state selections (MSS), a study by the method of pressure recovery (PRC).

A Comparative Reservoir Study of Zubair and Nahr Umr Formations in Subba Oilfield, Southern Iraq

The lower Cretaceous sandstones of Zubair and Nahr Umr formations are the main producing reservoirs in Subba oilfield in southern Iraq. Key differences in their petrophysical and depositional attributes exist affecting their reservoir characteristics. The evaluation of well logs and core porosity-permeability data show better reservoir properties in Nahr Formation. The Litho-saturation logs indicate greater thickness of oil-saturated reservoir units for Nahr Unr Formation associated with lower values of shale volume, and higher values of effective porosity. In addition, higher values of permeability for Nahr Umr Formation is suggested by applying porosity-irreducible water saturation cross plot. The reducing reservoir quality of Zubair Formation sandstones is related to finer grains of sandstone reservoirs, higher clay volume, and more effect of compaction resulting from greater depth. A reservoir layering scheme is proposed by sequence stratigraphic analysis leading to the identification of systems tracts and their key surfaces within Zubair and Nahr Umr formations, and forms the basis for predicting of reservoir architecture and quality. Laterally continuous, and thick amalgamated sandstone reservoirs are formed during highstand systems tract in Nahr Umr Formation as a result of low accommodation/sediment supply conditions. Within the transgressive systems tract of Zubair Formation, the sandstone reservoir bodies become isolated as accommodation exceeds sediment supply.

HORIZONTAL WELL COMPLETION SYSTEMS WITH MULTI-STAGE HYDRAULIC FRACTURING FOR LOW-PERMEABILITY, POORLY DRAINED, HETEROGENEOUS AND DISMEMBERED RESERVOIRS

Currently, the most effective method of intensifying the inflow of hydrocarbons and increasing oil recovery in productive formations in wells, in particular with a horizontal well, remains the technology of hydraulic fracturing (HF). In many regions, according to some domestic and foreign researchers, this is the only technology for developing fields with hard-to-recover hydrocarbon reserves confined to lowpermeability, poorly drained, heterogeneous and dissected reservoirs, which can significantly increase hydrocarbon production and make wells economically viable.Multi-stage hydraulic fracturing (MSHF) has established itself as one of the main methods of reservoir stimulation in the Russian Federation. The main goal of this method is to create highly conductive fractures in an oil and gas saturated reservoir throughout the horizontal section of the wellbore. To do this, an alternate series of hydraulic fracturing is performed, the result of which is the maximum production rate of hydrocarbons.Over time, oil and gas companies in the Russian Federation are becoming more demanding on the technical and technological parameters of MSHF in terms of the number of stages, the length of the horizontal section of the well, the possibility of re-fracturing and management of intervals/ports after its commissioning, and much more.The authors of the article propose to consider and analyze modern horizontal well completion systems with multi-stage hydraulic fracturing for low-permeability, low-drainage, heterogeneous and dissected reservoirs in order to form their rating.

ESTIMATION OF SATURATION OF PRODUCTIVE SEDIMENTARY RESERVOIRS OF THE WEST SIBERIAN FIELD WITH LOW RESISTIVITY VALUES

The main problem that is discussed in this article is related to the interpretation and analysis of low-resistivity productive reservoirs of the Vasyugan formation of one field in Western Siberia. A feature of the reservoirs of the Vasyugan formation is the underestimated values of the oil saturation coefficient. In this case, certain difficulties arise when determining the nature of saturation and justifying the position of fluid contacts in the formation.The work carried out a detailed analysis of the measurements results of physical properties on core samples, refined the petrophysical model and boundary values of parameters for interpreting this type of reservoirs of the Vasyugan formation. As a result of the research, the authors identified the most likely reasons for the underestimation of electrical resistivity values in productive reservoirs, which should be explained by the structure and fractional composition of rocks and the presence of pyrite. The authors propose a refined methodology with justification for new cutoff values of electrical resistivity and the use of a capillary model, which increases the reliability of the well logging data analysis on assessing the nature of saturation in low-resistivity productive formations and the depth of oil-water contacts.Certain recommendations are gave in the article for further research of the unconventional type of the Vasyugan formation, which include the coring and core analysis like granulometric, X-ray diffraction, studies of the mineral composition of clays and use of VIKIZ and multi-probe lateral logging and nuclear magnetic logging.According to the authors, this will increase the reliability of assessing the lithological composition of reservoir rocks and reservoir properties in lowresistivity oil-saturated reservoirs.

Adsorbed residual oil saturation and phase permeability relationship for oil in Western Siberia productive formations

Relevance. Relative phase permeabilities determine oil by water displacement mechanism, efficiency of productive formations flooding, dynamics of producing wells flooding. Relative phase permeabilities curves allow us to estimate the inflow nature according to geophysical well studies. Currently, relative phase permeabilities curves are constructed according to core samples laboratory studies. They are used to select a mathematical model describing the nature of the curves for a given productive reservoir. The most optimal option is to justify the individual relative phase permeabilities curve parameters. This option allows transition from the core sample level to the entire productive reservoir characteristics using geophysical well studies data. Aim. To substantiate a choice of a model describing the change in the relative phase permeability curves using field geophysics data based on the adsorbed residual oil saturation and phase permeability to oil relationship. Objects. Productive layers of individual deposits of the West Siberian oil and gas province, confined to the Lower Cretaceous deposits. Methods. Statistical processing of capillarimetric research data, analysis and substantiation of mathematical models describing relative phase permeability. Results. The paper shows that the permeability to oil at residual water saturation (the starting point of the relative phase permeabilities curve to oil) is determined by the adsorbed residual reservoir oil saturation. The authors have obtained the formula, linking the adsorbed residual oil saturation coefficient with the phase permeability to oil with residual water saturation. The adsorbed residual oil saturation is also closely related to the residual reservoir water saturation. Such relation is carried out through the reservoir clay content. The authors proposed the technique that allows residual oil saturation by type structuring and mobility degree. This technique allows as well as finding out the residual reserves of mobile oil distribution to justify the recovery techniques.

Multi-objective optimization of reservoir development strategy with hybrid artificial intelligence method

Optimization of subsurface hydrocarbon production holds paramount importance for decision-makers as it determines crucial development strategies such as optimal well placement and well control parameters (e.g. injection/production rates of injectors and producers). Despite the availability of numerous established optimization methods in this field, traditional reservoir production optimization methods face challenges in simultaneously addressing multiple development objectives and coordinating the interaction of well control parameters in different control steps. In this work, we construct a hybrid artificial intelligence method to jointly optimize well placement and well control parameters, taking into account two development objectives and dynamic optimization. It consists of two stages. First, a reservoir potential map is generated with the production potential formula that considers reservoir pressure, remaining oil saturation and other reservoir properties (permeability, hydrocarbon column height) etc. The reservoir potential map provides guidance for placing well in medium to high potential areas and engineering constraints for the optimization process. Then, a hybrid artificial intelligence method that couples deep learning method (Long and Short Term Memory (LSTM)) and multi-objective optimization algorithm (Non-dominated Sorting Genetic Algorithm II (NSGA-II)) is established to seek a compromise between the two objectives in water-flooding processes. The LSTM neural network is trained as the surrogate model to replace the high-fidelity simulator to achieve high efficiency of overall optimization workflow. The NSGA-II algorithm is employed for handling the joint optimization problem of well placement and well control parameters by maximizing the cumulative oil production and minimizing the water cut. The performance of the proposed method is tested on one benchmark function and two reservoir models. On the 2D synthetic reservoir model the optimized scheme leads to a notable increase of 3 × 104 m3 in cumulative oil production, accompanied by 17 % reduction in water cut when contrasted with the base scheme. Similarly, within the 3D reservoir model, the optimized scheme results in a substantial enhancement, boosting cumulative oil production by 14 × 104 m3 and reducing water cut by 20% compared to the base scheme. Moreover, the proposed method surpasses alternative multi-objective optimization (MOO) algorithms by demonstrating 82% and 95% reduction in optimization time, respectively. The results demonstrate that this method can provide the optimal water-flooding strategies under the premise of different development objectives. The Pareto front (or optimal solutions) generated by the hybrid method offers a variety of diverse water-flooding strategies to assist subsurface engineers in making informed decisions.

An enhanced accuracy method for monitoring formation water salinity utilizing elemental spectroscopy logging

The accurate determination of formation water salinity is crucial for petroleum exploration and development, as it plays a significant role in determining reservoir parameters. The salinity of formation water affects physical parameters such as resistivity and Sigma, which are essential in calculating reservoir oil saturation. Therefore, this paper proposes an effective calculation method of formation water salinity based on elemental spectroscopy logging technology. The method starts by accurately calculating the formation chlorine (Cl) content through a combination of inelastic and capture energy spectrum analyses. Subsequently, a high-precision calculation model of formation water salinity is constructed by utilizing formation density and porosity information. Compared to the traditional oxide closure model, the joint bispectral method improves the calculation accuracy of Cl content by an order of magnitude and keeps the calculation error of formation water salinity within 2 g/L. The field logging example further demonstrates the high agreement between the calculated results of formation water salinity and laboratory analysis results, validating the accuracy of the joint bispectral method. This method is not affected by the mineral composition of the formation, making it suitable for a wide range of applications and highly versatile, which provides valuable technical support for the exploration and development of oil and gas in saltwater-bearing reservoirs.

3D-MODELING TECHNOLOGY OF INITIAL OIL SATURATION IN TRANSITIONAL OIL-WATER ZONE BY COMPLEX OF CAPILLARIMETRY AND ELECTRIC LOGGING METHODS

Link for citation: Potekhin D.V., Shiryaev E.O., Galkin S.V. 3D-modeling technology of initial oil saturation in transitional oil-water zone by complex of capillarimetry and electric logging methods. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 98-107. In Rus. The relevance. The 3D distribution of the initial oil saturation in the reservoir volume is one of the key elements of geological and technological modeling, largely determining the quality of subsequent development design solutions. The publication presents an analysis of the current state of the problem of studying the oil-water transition zone and the distribution of oil saturation. For terrigenous hydrophilic reservoirs, electric lateral logging quite reliably controls the fluid saturation of the void space of the oil part of the deposit, which suggests the possibility of its integration with widely used capillarimetry methods. Aim: to evaluate the possibility of reliably determining the oil saturation of terrigenous hydrophilic reservoirs by combining the data of electrical lateral logging, filtration-capacitance properties of reservoirs and capillarimetric core studies, to build a 3D model of the distribution of the initial oil saturation of reservoirs in oil deposits, taking into account the allocation of the oil-water transition zone. Object: oil-saturated reservoirs of the Visean oil deposits of the Perm region. Method: methods of multidimensional mathematical modeling in the development of a methodology for determining the initial oil saturation of reservoirs based on a complex of well logging and capillarimetric studies of the core, construction of 3D distribution of the initial oil saturation of the reservoir, taking into account the parameters of the oil-water transition zone. Results. The authors, based on the developed methodology for the deposit of the reservoir Bb of the Aspinskoe field, built a 3D model of the distribution of the initial oil saturation. For the studied reservoir, they carried out the analysis of distribution of zones of free saturation, undersaturation, transition zone and limiting oil saturation. The resulting 3D model can be used in geological and technological modeling of the development of an oil deposit.

Feasibility study of crude oil mobilizing with nano emulsion in low oil saturation reservoir

The Chang 8 low oil saturation reservoir in Changqing Oilfield is highly heterogeneous and rich in organic matter, resulting in complex pore wettability. At present, when guar fracturing fluid is used for development, the wetting modification capacity of fracturing fluid is weak, the effect of imbibition on enhancing oil recovery (EOR) is poor, and the mobilization ratio of large pores oil is only 5.40%, and the total recovery rate in lab is less than 25%. There is an urgent need for a highly efficient oil mobilization reagent with strong modification capacity and capable of simultaneously mobilization core micro and nano-pore crude oil. Through relative permeability displacement and forced imbibition, it is found that the residual oil saturation of core is 29.87%. However, the oil saturation range of Chang 8 reservoir is only 12.2%–33.2%, and it is the main reason for the difficulty in mobilizing crude oil. Then, based on different types of chemical reagents, 0.10% KX-7 oil mobilization reagent is optimized through the nuclear magnetic resonance (NMR) method. The particle size of 0.10% KX-7 nano emulsion is about 10 nm, the imbibition recovery rate is 44.24%, and the mobilization ratio of small pores (nano-scale) and large pores (micro-scale) is 45.52% and 35.73% respectively, and the wettability angle of core is modified to 44°, which can reduce the residual oil saturation of the core to 18.20%. Its main mobilization mechanism is wetting modification and solubilization. Increasing reagent concentration, temperature, and pressure can promote the mobilization and modification capacity of KX-7 nano emulsion, and the mobilization ratio of crude oil is further increased by more than 10%. The optimized KX-7 nano emulsion has a good performance in the field test with a daily output of 28.2 tons, which can guide the highly efficient development of low oil saturation reservoirs.

Correlation between filtration-capacitance and thermal properties of oil-saturated reservoirs of extra-viscous oil deposits (SVN). Adabtation of hydrodynamic model.

Correlation between filtration-capacitance and thermal properties of oil-saturated reservoirs of extra-viscous oil deposits (SVN). Adabtation of hydrodynamic model.

Methodological improvement for determining the oil saturation of reservoirs using electrical logging

Methodological improvement for determining the oil saturation of reservoirs using electrical logging

Analysis of the implemented development system effectiveness, horizontal wells drilling and well interventions in the conditions of carbonate deposits of the Tournaisian tier of the Znamenskoye oil field

he paper analyzes the implemented system for the oil deposits of the Tournaisian tier of the Znamenskoye field development, as well as factors reducing its effectiveness, assessment of the features of the geological structure affecting oil production, and the development of proposals to improve the development system efficiency. It is noted that during the development of the field, the geological structure of the Tournaisian tier oil deposits has significantly changed because of the additional study of the development facility, the high efficiency of the use of horizontal wells has been confirmed. It shows an increase in the initial well flow rate and the specific accumulated oil production per meter of oil-saturated reservoir thickness, a decrease in the initial water content of well production, the growth rate of water content, a decrease in the accumulated oil-water factor for the first year of well operation, depending on the increase in the capacity of the bridge between the oil and water-saturated layers. Keywords: oil reserves production; bridge; oil recovery factor; oil-water factor; well.

Modeling Water Injectivity Tests under Multiple Rate Schedule: An Approximate Solution

Summary An injectivity test consists of continuously injecting a phase (water or gas) into an oil-saturated reservoir during a period. According to the analysis of the wellbore pressure behavior, this procedure estimates reservoir parameters, such as permeability and skin factor, and the volume of recoverable oil. In this context, this study proposes an approximate analytical solution for the pressure behavior during a water injectivity test on a multilayer reservoir considering multiple injection flow rates. The accuracy of the proposed solution was evaluated through comparison with a commercial finite-difference-based flow simulator in different scenarios. The results indicate a considerable agreement between the data provided by the numerical simulator and the proposed model. In addition, we successfully estimated the equivalent reservoir permeability using the proposed model with satisfactory results.

Thermal effect of acoustic impact on the oil reservoir

The paper considers the effect of heating an oil-saturated reservoir during the propagation of high-frequency acoustic waves in it, due to their absorption by a saturated porous medium. It is assumed that in this case, volumetric heat sources are created in the reservoir. The density of distribution of heat sources in a porous medium at various capacities and frequencies of acoustic waves is shown. The paper presents a mathematical model for calculating the temperature field in a porous saturated medium under acoustic influence with an emitter located opposite the treated reservoir. It is assumed that the radius of the acoustic radiator is equal to the radius of the well, and the length of the radiator is equal to the power of the treated reservoir. In addition, the effect of increasing the effective thermal conductivity of the formation is taken into account when calculating the distribution of the temperature field. It is believed that the well works without stopping with a certain oil flow rate, depending on the viscosity of the oil. The problem is solved by the numerical method of finite differences according to an implicit scheme in a cylindrical coordinate system. In this paper, the author presents the results of studies of thermal effects occurring in the formation, namely, an increase in the effective thermal conductivity of the formation and the occurrence of heat sources during the propagation of acoustic waves in the formation. Thus, the article presents the results of computational studies that take into account only thermal effects during the treatment of the formation by the wave (acoustic) method. The treatment of the reservoir by wave methods (acoustic, sound, water hammer, elastic, and so on) is one of the promising methods for both increasing oil recovery and intensifying oil production, therefore, the theoretical study of the processes arising from the interaction of waves with a saturated porous medium is significant.

Stability conditions of oil-saturated reservoirs porosity with deep overlaying

Stability conditions of oil-saturated reservoirs porosity with deep overlaying

INCREASING EFFICIENCY OF THE DISPLACEMENT OF HIGHLY RESINOUS OILS BY POLYMER SOLUTIONS

The article presents the experimental results of studies of the filtration properties of oils from fields with a high content of asphaltene-resinous substances. Experimental studies of the filtration process of deposits with a high content of asphaltene-resinous substances have established that in low-permeability, unlike high-permeability reservoirs, the beginning of filtration proceeds according to a nonlinear law, and with an increase in the pressure gradient, the nonlinearity turns into a straight line corresponding to the Darcy law. In addition, the results of experimental studies on the displacement of oil from fields with a high content of asphaltene-resinous substances by polymer solutions on artificially created reservoir models are presented to determine the concentration of the polymer solution and the size of the slug to increase oil recovery from reservoirs. Experimental research on oil displacement by polymeric solutions were carried out on reservoir models filled with quartz sand, while the analyzed deposits are represented by carbonate limestone rocks. The results obtained on the oil displacement by polymer solutions on reservoir models with terrigenous reservoirs are considered possible for use on objects with carbonate reservoirs with a qualitative justification for the introduction of the polymer flooding method. Experimental studies on the oil displacement from fields with a high content of asphalteneresinous substances with a thickened water rim have established that this method gives the greatest increase in anhydrous and ultimate oil recovery, within a change in the concentration of the polymer solution of 0.2-0.4%, with a rim size of more than 70% of the oil-saturated reservoir volume. Studies on the displacement of high-viscosity oils with polymer solutions have shown that the use of this method of increasing the oil recovery factor in practice is not always economically feasible, due to the need to provide high injection pressures and a high concentration of an expensive polymer solution.

ГЕОДИНАМІКА

The purpose of the research is to analyze the impact of the region's geodynamics on the formation of hydrocarbon reservoirs in the carbonate Lower Visean-Tournaisian stratum. The paper is focused on the substantiation of hydrocarbon traps within the Machukhy-Tyshchenky area of the southern zone of the Dnieper-Donets basin, as well as oil and gas exploratory drilling and new effective methods of stimulating gas inflows to boreholes. Methodology. The study applies the stratigraphic, lithological, tectonic, paleotectonic methods of studying geology and oil potential, as well as the method of geological analogies. Results. Gas-bearing carbonate rocks of the Early Visean-Tournaisian age in the Machuhy-Tyshchenky area have been studied. A comparison with other oil and gas regions has shown that they are the domes of carbonate platforms (Wаulsoгtiаn facies). Three echelons of bioherm limestones have been identified within the the area. The research helped to describe the stages of their formation and determine the dependence of reservoir properties of limestones on their biofacial types. The role of tectonic fracture in the formation of reservoir rocks is shown. As a rule, tectonic fractures are cemented by calcite under the action of formation waters. An assumption is made about the formation of microfractures in dense limestones due to the action of plumectonic. It consists in the intrusion of high-energy fluids from the depths of the earth, the natural fluid fracturing of rocks and the formation of non-anticlinal hydrocarbon accumulations in them. Probable places of fluid breakthrough may be zones of deep faults: the Ingulets-Kryvorizhzhya-Krupetsk fault zone crosses Machuhy-Tyshchenky area. Filling microfractures with hydrocarbons prevents their cementation. The paper gives examples of microfracturing in the cores of boreholes and establishes reduced core from microfracture intervals. To identify microfracturing intervals in carbonate rocks, it is proposed to use information on the reduction of core, as well as the speed drilling of rocks. The study suggests using multistage hydrofracturing and acid hydrofracturing in order to stabilize and increase gas influxes from carbonate reservoirs to the boreholes. Such technology should provide the connection between the borehole and oil-saturated reservoirs. Probable factors of negative impact on the environment during hydrofracturing have been identified. Originality. Adiabatic microfracturing of dense lithotypes of rocks is possible at considerable depths, in addition to tectonic fracturing. It is due to natural fluid fracturing of sedimentary strata by hydrocarbon gases. This gives hope for the discovery of new types of hydrocarbon deposits that are not associated with anticline traps. Practical significance. Geophysical surveys and the location of six boreholes are recommended in order to search for hydrocarbon deposits in the Machuhy-Tyshchenky area. The study suggests effective methods for increasing gas influxes to boreholes from low-permeability carbonate rocks.