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Vol 24, No 4 (2024)

ARTICLES
The Potential Applications of Electron Microscopy in Studying the Lithological Characteristics of Oil-Bearing Sandstones
Osovetsky B.M., Kazymov K.P., Galkin S.V.

Abstract

The purpose of the research is to apply a technique for studying of the void space in potentially oil-bearing reservoirs using electron microscopy. Microscopic studies of characteristic areas of the core surface are carried out with an assessment of the void space microstructure, the characteristics of the fragmentary framework grains and filler, and the microstructure of the cementing substance. The surface of the samples is scanned at different magnifications, and microprobe analysis is carried out to diagnose the grains of the detrital framework, filler, cementing and newly formed substances. The relationship between the filtration and capacitance properties of reservoirs and the characteristics of the granulometric composition, void space, composition and structure of cement has been studied. A number of groups have been identified in the Solikamsk Depression reservoirs, for which a regular relationship between productivity and the features of granulometric composition, void space, composition and structure of cement has been established. The first group of reservoirs is characterized by good sorting and dense packing of quartz detrital framework grains, a small amount of filler particles and cementing substance represented by kaolinite with "book-like structure" type. Reservoirs with reduced permeability are characterized by an increased proportion of cementing substance, poor grain sorting due to the presence of a significant amount of filler particles in the detrital framework. A characteristic feature of such a reservoir is a less perfect microstructure of kaolinite of the "book-like structure" type. For the studied siltstones, an mixed-grained granulometric composition, no grain sorting by size, unstructured kaolinite cement with no "book-like structure" type have been established. The lithological differences of sandstones of the same geological age, determining their oil-bearing capacity, are determined by the important role of the facies environment of sedimentation and subsequent processes of rock transformation at the stages of diagenesis and catagenesis. The electron microscopy method can be recommended for wider application in oil and gas geology when assessing the lithological features of oil and gas reservoirs.
Perm Journal of Petroleum and Mining Engineering. 2024;24(4):178-185
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Forecasting the placement of horizontal and directional wells depending on the geological structure of the low-permeability formation YUS2
Korepanov S.E.

Abstract

This study investigates the construction of a probabilistic-statistical model using two reference areas of field X, drilled with horizontal and deviated wells. The model involves discriminant analysis combined with the development of both linear and multivariate regression relationships to predict well locations within the undrilled area and potentially forecast initial oil production rates. The impact of geological structure on well placement is analyzed using a t-test for comparing means. Based on identified differences in the geological structure at well locations, discriminant analysis was conducted to determine the factors influencing well type selection. The analysis revealed that the areas differ in geological structure, and porosity, permeability, and sand content of the formation influence the placement of horizontal and deviated wells. Linear and multivariate regression analysis was performed to classify the territory into zones with distinct geological structures. Linear regression analysis indicated that oil production rates in low-permeability reservoirs are differentiated into three classes with varying parameter influences within each production rate range. Multivariate regression analysis enabled the assessment of the combined influence of the most statistically significant formation characteristics on oil production rates and provided multivariate regression equations for predicting oil production rates of horizontal and deviated wells.
Perm Journal of Petroleum and Mining Engineering. 2024;24(4):186-193
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Application of Geomechanical Modeling Methods to Assess Casing Stability during Cumulative Perforation
Chernyshov S.E., Popov S.N., Xiaopu W., Hailong Z., Derendyaev V.V., Melekhin A.A.

Abstract

The stability analysis of the lining for two oil producing wells during secondary opening of productive formations using the cumulative perforation method was performed. The research was carried out using data from direct measurements of wellbore pressures at different distances from the cable tip of the perforating device at the time of detonation, which exceeded 50 MPa. The pressure values were approximated along the wellbore using a power dependence. For a reliable forecast of the stress-strain state of the near-wellbore zone of the perforation interval, the ANSYS finite element modeling software package was used. To determine the stress field, an axisymmetric finite element calculation scheme was built; the height of the model along the wellbore was 39 m. When modeling, it was taken into account that the geological and physical characteristics of the modeled formations differed in the depth of occurrence and the value of the formation pressure. The elastic-strength properties of the formed cement stone were determined in the course of laboratory experiments for various formulations of cement slurries. Based on the modeling results, the destruction areas and the strength margin of the cement stone were determined, as well as the values of radial displacements of the production string in the perforation interval. The developed model of the borehole zone and methodological approaches can be used in the future when choosing the optimal elastic-strength properties of the cement stone, perforation devices and technological parameters of perforation-explosive operations.
Perm Journal of Petroleum and Mining Engineering. 2024;24(4):194-203
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Comprehensive Analysis of Methods for Assessing the Bottomhole Zone of Wells Operating Complex Carbonate Reservoirs
Chernykh V.I., Galkin V.I., Ponomareva I.N., Martyushev D.A.

Abstract

Assessing the hydrodynamic state of bottomhole zones is a key task to be solved when conducting and interpreting hydrodynamic well studies. The most widely used indicator of the condition of bottomhole zones in practice is the skin factor. However, its definition for the conditions of complex carbonate reservoirs is often accompanied by difficulties. Under conditions of incomplete pressure recovery, typical for the conditions under consideration, the value of the skin factor often takes on an unreliable value, in some cases leading to an incorrect interpretation of the state of the bottomhole zone, regardless of the approaches used to interpretation. Using actual data as an example, the article demonstrates that a reduction in the pressure recovery curve leads to false negative skin factor values both when implementing the tangent graph-analytical method and when processing in accordance with Bourdais's theory. In such conditions, it is recommended to use fundamentally different indicators of the state of the bottomhole zones, for example, a dimensionless diagnostic feature determined when implementing the method of deterministic moments of pressure. However, the lack of experience in the widespread practical application of this method necessitates an assessment of its reliability. For this purpose, this article uses an effective tool of mathematical statistics - multiple regression analysis, which, in this case, was reduced to the construction of multidimensional models of well flow rates. The geological and technological indicators of well operation were used as independent variables, including parameters characterizing the bottomhole formation zone (skin factor determined in the KAPPA Workstation software product (Saphir module), skin factor calculated using the tangent method, as well as a dimensionless diagnostic feature). According to the theory of regression analysis, the parameter that is included in the constructed model at the earliest possible step is reliable. The procedure for constructing and analyzing multidimensional statistical models performed in this work demonstrated the reliability of a dimensionless diagnostic feature in assessing the state of bottomhole zones of productive formations represented by complex carbonate reservoirs.
Perm Journal of Petroleum and Mining Engineering. 2024;24(4):204-211
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Systematic Analysis of the Results of Studying a Technogenically Formed Spatially Heterogeneous Drainage Zone of Horizontal Wells
Kazantsev A.S., Ozhgibesov E.S., Galkin V.I., Kolychev I.Y.

Abstract

Carbonate deposits of the Bashkirian Stage in Perm Krai are characterized by a high degree of heterogeneity, which makes it difficult to develop oil reserves evenly. Acid treatments are currently one of the most popular methods of regulating development in carbonate reservoirs. However, in conditions of layeredheterogeneous sediments the most permeable part of the section is mainly affected, while the low-permeable part of the section remains uninvolved in the development process. In this connection, it is an urgent task to predict the degree of impact of acid treatment on individual reservoir layers. The purpose of this study was to create mathematical models for predicting the skin factor of the reservoir after acid treatment. As input data we used skin factor determinations in reservoirs and geologic characteristics of these reservoirs: porosity coefficient, permeability coefficient, oil saturation coefficient and reservoir thickness. Mathematical modeling methods were used in the study: stepwise regression analysis, construction of probabilistic-statistical models. According to the results of statistical analysis it was revealed that reservoirs are divided into two classes, in which the formation of the skin factor value depends on different characteristics of the reservoir. To determine the class to which the reservoir formation belongs, univariate probabilistic-statistical models were built and subsequently combined into a single complex model. For each identified class, regression models were developed to predict the skin factor of the formation after acid treatment. The obtained mathematical models can be applied in the design of geological and technological measures, as well as to improve the accuracy of hydrodynamic modeling by taking into account the values of skin factors in the bottomhole zone in the adaptation of the model.
Perm Journal of Petroleum and Mining Engineering. 2024;24(4):212-218
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The migration of Colloids as a Cause of Deterioration of Permeability in Porous Sandstones during Laboratory Investigations
Shcherbakova I.S., Kozhevnikov E.V., Shcherbakov A.A.

Abstract

Rock permeability is not a constant value, it depends on many factors, including the presence of small particles in the fluids and porous medium - colloids that can clog pore channels and reduce permeability. The effect of natural colloids migration, as a rule, is not taken into account when determining the dependencies of permeability on effective pressure, this phenomenon is often ignored by many authors and interpreted as a result of the influence of other factors. The reason for insufficient attention to the fact of mobilization and migration of natural colloids is the difficulty of identifying this phenomenon. It was found that with a change in the effective pressure in the initial period of oil production in real conditions, permeability can decrease more than according to laboratory studies. With a small change in effective pressure, when the probability of a decrease and hysteresis of permeability due to deformation of the porous reservoir is extremely small, the dependencies of permeability on the amount of oil produced were established. This fact confirms the probability of the influence of migration of natural colloids on the decrease in permeability and emphasizes the need to study it. The aim of the work is to study the effect of colloid migration on the permeability of porous sandstones with changes in the fluid injection rate and pore pressure. The article presents the methodology and results of core filtration tests taking into account the decrease in the permeability of the porous medium caused by the migration of natural colloids during fluid injection. The conditions of filtration tests exclude other permeability factors, such as creep and chemical mobilization of colloids. The results obtained demonstrate the dependence of permeability on colloid migration with changes in the fluid injection rate and pore pressure. Filtration studies of core samples using the proposed technique showed that the permeability of the cores decreases only with fluid movement inside the samples, which is direct evidence of pore clogging due to the migration of natural colloids. It was found that a decrease in pore pressure leads to a more intense decrease in permeability during injection, which indicates additional mobilization of colloids. Porous media with higher permeability are less sensitive to colloid migration and changes in pore pressure.
Perm Journal of Petroleum and Mining Engineering. 2024;24(4):219-230
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Hydrophobization of the Reservoir Surface in the Processes of Impact on the Bottomhole Formation Zone. Part 2. From Capillarity to Reality
Glushchenko V.N., Turbakov M.S., Khizhnyak G.P.

Abstract

The established opinion in the literature on the need for hydrophobization of the reservoir surface in the bottomhole formation zone (BFZ) when injecting aqueous process fluids into it, in particular, cationic surfactants (CS), to increase the relative phase permeability for oil and reduce it for water is refuted by the results of bench experiments on polymict cores. It was established that there was no additional washing of oil with a CS solution, a decrease in oil mobility with bound water under conditions of higher oil saturation than with ordinary water, and an increase in water mobility after exposure to a CS solution by more than two times. A conclusion was made about the potential applicability of CS in aqueous solutions at the stages of perforation and well killing with high oil saturation of the BFZ. The best option for increasing the relative phase permeability of oil over water should be recognized as its simple hydrocarbon saturation. The essence of capillary processes and the significance of capillary pressures actually occurring in reservoir conditions of heterogeneously wetted reservoir space for aqueous liquids with respect to well killing are briefly considered. The inclusion of capillary forces in the consideration of this process against the background of hydraulic pressure actually acting in the BFZ indicates their insignificant role, which follows from the analytical calculations carried out in the work. The accepted methods of laboratory assessment of capillary impregnation of porous media at atmospheric pressure after their treatment with solutions of CS do not stand up to criticism. The obvious inconsistency of many theses of "hydrophobization" of the BFZ stems from incorrect assumptions about the fundamental provisions of reservoir fluids filtration through heterogeneously wetted reservoir space and adsorption processes of surfactants on rocks, which will be described in detail further in Part 3.
Perm Journal of Petroleum and Mining Engineering. 2024;24(4):231-239
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Modeling the Stability of a Large-Volume Underwater Liquid Hydrocarbon Storage Tank
Zemlyanovskiy V.A., Popov S.N., Chernyshov S.E.

Abstract

Climate change and the reduction of sea ice in the Arctic Ocean allow scientists and engineers to think about the development of undiscovered hydrocarbon reserves, most of which are currently located in the Arctic. Underwater storage tanks are an important element of the infrastructure that can provide strategic storage of hydrocarbons in emergency situations or supply disruptions, as well as develop oil and gas reserves. The paper considers underwater oil storage tanks as one of the stages that will allow the exploitation of offshore fields underwater. The use of underwater storage tanks can contribute to a more sustainable and safe development of the oil and gas industry, reduce environmental risks and increase economic efficiency. In the course of the study, a numerical finite element model of the underwater storage tank was developed in accordance with the patent of M.S. Sonin. A numerical analysis of the stress-strain state of the storage tank with a capacity of 120,000 m3 was carried out and the distribution of stresses in the dome and foundation of the tank was estimated taking into account the features of the underwater structure. The main reasons leading to the loss of stability, destruction of the tank and foundation were identified. The most vulnerable part of the tank was the junction of the bottom and the wall, made with welded seams. For the foundation, the most dangerous sector is where the tank wall is monolithic into the foundation slab - here, maximum stresses of both compression and tension are observed. There are two possible approaches to leveling this problem: reduce the immersion depth of the storage facility, increase the thickness of the dome part of the body and add stiffeners to increase the rigidity and stability of the structure. However, both of these technical solutions will lead to additional costs and technological difficulties during the implementation of the project.
Perm Journal of Petroleum and Mining Engineering. 2024;24(4):240-246
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Research of Reliability Criteria of Frozen Wall in Monitoring and Control of Artificial Ground Freezing
Pugin A.V., Ageeva K.M., Bublik S.A.

Abstract

Three thermodynamic criteria of frozen wall reliability are investigated, which determine and combine its thickness and temperature in different ways. Boundary isotherms for different criteria are determined based on 1) the freezing temperature of porous water; 2) the temperature for which the frozen wall thicknesses were calculated based on strength and creep conditions, and 3) a floating temperature value determined as a supremum of a zone with a given average temperature inside the frozen wall. The considered criteria are used in the process of thermal monitoring of the frozen wall statement when assessing its bearing capacity. Each criterion was described in detail, the sufficient conditions for the reliability of the frozen wall associated with it were presented, and the problem of optimal control of the coolant temperature increasing, which could be solved with its use, was presented. A comparative analysis of the criteria was carried out from the standpoint of optimal control of the artificial freezing regime, ensuring the minimum possible energy costs for the frozen wall holding during its life cycle while maintaining the required safety of mining operations. The "optimal" graph for the coolant temperature increasing within each criterion was determined by a series of numerical calculations of the thermophysical problem in the specialized software product "FrozenWall". Based on the results of the study, the third, most flexible criterion with a floating temperature value determining the boundary isotherms of the frozen wall as a supremum of a zone with a given average temperature was recommended for practical application. For the other two criteria, the temperatures of the frozen wall boundaries are rigidly fixed, which significantly limits the upper limit of the increase in the temperature of the coolant in the brine network and leads to lower energy efficiency of the freezing system as a whole. The results of the work will be useful to specialists in the field of thermal monitoring in the construction of mine workings using the method of artificial ground freezing.
Perm Journal of Petroleum and Mining Engineering. 2024;24(4):247-259
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Geological Model of the Mechanism of Formation of Gas-Dynamic Hazard Centers in the Rocks of the Sylvinite-Carnallite Zone at the Verkhnekamskoye Potassium-Magnesium Salt Deposit
Andreiko S.S., Lialina T.A.

Abstract

In the course of the research, a geological model of the mechanism of formation of gas-dynamic hazard centers in the rocks of the sylvinite-carnallite zone at the Verkhnekamskoye potassium salt deposit was developed. During the formation of gas-dynamic hazard centers in the rocks of the sylvinite-carnallite zone, the sources of gas-saturated fluids were gas-bearing aqueous solutions, including fluids from oil-bearing deposits located in the thickness of rocks underlying the salt deposit. The paths of ascending migration of gas-saturated fluids could be: rupture tectonic faults, thrusts, through zones of increased fracturing and permeability zones above the slopes of reef structures. Migration of gas-saturated fluids into the salt thickness from the underlying rocks occurred in a subvertical direction (from the bottom up). In the rocks of the sylvinite-carnallite zone, the lateral direction of migration of gas-saturated aqueous solutions prevailed over the vertical one due to the pronounced anisotropy of filtration properties. Fluids moved laterally along numerous clay layers, interlayers and intergranular space. During the migration of gas-saturated fluids in the rocks of the sylvinite-carnallite zone, epigenetic transformations of salt rocks occurred: replacement of sylvinites with rock salt, sylvinization of carnallites, formation of rocks of mixed composition (sylvinite + carnallite). During sylvinization of carnallites, the migration of aggressive gas-saturated fluids occurred in the direction from the zones of replacement of sylvinites with rock salt and variegated sylvinites in the direction of development of carnallite rocks. Variegated sylvinite as a product of epigenetic processes in rocks of the sylvinite-carnallite zone near the contact with carnallite rock has increased porosity and decreased strength. The patterns of free gas distribution in the layers of the sylvinite-carnallite zone are determined by the work of the three-zone functional system of halogen metasomatism. The decomposition of carnallite was accompanied by the formation of a deficit of the solid phase, the value of which could vary in a wide range of values and reach almost 70%. In areas of complete decomposition of carnallite in rocks of the sylvinite-carnallite zone, voids were formed due to the deficit of the solid phase. These voids, by analogy, can be considered a process of natural “undermining” of the overlying layers and “overmining” of the underlying ones. The effect of natural “undermining” was accompanied by the formation of crack systems in the undermining part of the sylvinite-carnallite zone due to unloading from rock pressure and rock displacement, through which free gases migrated into the undermining layers. As a result, in the rocks of the sylvinite-carnallite zone, under the influence of natural “undermining”, in the zone of unloading from vertical stresses due to destruction and stratification at the contacts of layers and layers, as well as along clay interlayers, favorable conditions are created for the filtration of free gases into it.
Perm Journal of Petroleum and Mining Engineering. 2024;24(4):260-269
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