Volga-Ural Oil Research Articles

Features of laboratory study of the core of weakly cemented reservoir rocks

Background. Currently, there is a problem of studying intervals represented by weakly cemented core, although such rocks can be the main reservoirs. Lack of reliable petrophysical information leads to underestimation of the main parameters of porosity and permeability, which in the future is likely to lead to incorrect estimation of hydrocarbon reserves. The relevance of the work is due to the lack of unified regulatory and methodological approaches to the research of weakly cemented core material. Objective. To develop our own methodological approach by selecting technologies and techniques, which allows to carry out primary preparation, sampling, profile measurements and petrophysical studies of weakly cemented core. Materials and methods. We used weakly cemented core from the Volga-Ural oil and gas province and conducted the research in accordance with the requirements specified in the guidelines for laboratory tests using necessary supplies. The methods considered in the article cover the time interval from the early 2000s. Results. In the course of the work, standard methods of core investigation were considered, and the possibility of their application to the samples of weakly cemented rock was evaluated. The peculiarities of sample preparation and research on weakly cemented core were also revealed. Conclusions. A methodological approach was developed that allows primary preparation, sampling, profile measurements and petrophysical studies of weakly cemented core.

Oil and gas reservoirs in clinoforms of the Kolgan strata in the Volga–Ural oil and gas province: Forecast and survey technologies

Oil and gas reservoirs in clinoforms of the Kolgan strata in the Volga–Ural oil and gas province: Forecast and survey technologies

ASSESSMENT OF THE IMPACT OF WELL GRID DENSITY ON OIL RECOVERY UNDER CONDITIONS OF UNCERTAINTY

The density of the well grid is one of the most important parameters that has a significant impact on the rate and amount of oil reserves extraction. As practice shows, existing approaches to the reliable assessment and identification of the degree of influence of this indicator on oil recovery do not allow us to adequately form an idea of the dynamics of reservoir processes and their role in making managerial decisions in conditions of uncertainty. Taking into account the decrease in the number of hydrodynamic and geophysical studies conducted in relation to the total number of wells in operation at fields that are being developed for a long time or just being put into development, the issue of predicting the oil recovery coefficient according to the list of geological and field parameters remains open and requires an urgent solution, including those related to the use of unique complex algorithms. The purpose of the work is to determine the relationship between the density of the well grid and the final coefficient of oil recovery in the development of fields in natural conditions using computer modeling systems. The research methodology consists of the use of existing scientific and methodological approaches to the processing of geological and commercial information in conditions of different densities in combination with the use of various advanced systems for identifying hidden patterns. Geological and statistical models have been defined for the oil deposits of the Famensk tier of the South Tatar arch of the Volga-Ural oil and gas province, allowing for the forecasting procedure for groups of objects identified during differentiation, subject to the dynamic density of geological and field information and various technical and economic indicators of field development. A comprehensive interpretation of the nature and degree of influence of geological and technological parameters on the amount of oil reserves production has been carried out. The need for preliminary differentiation of deposits based on identification with the subsequent use of the presented geological and statistical models to reduce the risks of making erroneous decisions during activities aimed at optimizing the development of analog facilities and rational extraction of residual oil reserves is reliably substantiated.

FEATURES OF WELL KILLING IN CONDITIONS OF CARBONATE RESERVOIR AND HIGH GOR

The article presents the results of studies on the use of well killing technology in fractured carbonate reservoirs of the Republic of Bashkortostan under conditions of loss of kill fluid and high GOR of the product. The geological and technical conditions of the Metelinskoye field are summarized, and the factors complicating well killing before routine and workover are described - reduced reservoir pressure during operation, previous large-volume salt-acid treatments, and the presence of hydrogen sulfide.The article substantiates the choice of invert-emulsion solutions (IER) for killing wells in the Metelinskoye field, taking into account the experience of using various killing technologies in the Volga-Ural oil and gas province. The authors have determined the physicochemical and rheological characteristics of kill compositions based on IER of various densities. An increase in the effective viscosity at high shear rates and the limit shear stress of the IER with an increase in the density of the composition was revealed. Taking into account the high risks of gas breakthrough during well killing in the Metelinskoye field, studies were also conducted to assess the gas-retaining capacity of the IER on an experimental installation by extruding the composition from a metal capillary. It has been shown that the gas holding capacity of these compositions with increasing density is described by an equation with a power function and a high degree of reliability. The effect of hydrogen sulfide neutralizer addition on IER properties was investigated. In order to increase the success of killing, the IER-based killing technology was selected and adapted to the existing conditions. The better blocking ability of higher density formulations has been confirmed. Successful well tests. To reduce the risks of using the IER and optimize the consumption of reagents during the further use of the technology, organizational and technical measures for killing and subsequent repair of wells were developed and implemented. The results of this work can be used in wells of the Ural-Volga region, Eastern Siberia and Timan-Pechora province with the presence of losses and a high gas factor, the repair of which is complicated by the lack of fluid circulation and the presence of excess pressure at the wellhead with signs of gas shows.

Reducing the risks of making erroneous decisions when managing the development of deposits in carbonate reservoirs

To reduce the risks of making erroneous decisions aimed at improving the efficiency of oil deposits development in the carbonate reservoirs of the Volga-Ural oil and gas province, it is proposed to use the analogy method. An algorithm has been developed that allows using analog objects or groups of them to solve various fishing tasks. The search is proposed to be carried out using 20 parameters characterizing the geological, physical and physico-chemical properties of the formations and the fluids saturating them. The deep differentiation of objects allows to increase the degree of identification of objects. Keywords: Volga-Ural oil and gas province; analogy method; differentiation; grouping; carbonate reservoirs.

CREATION OF AN ALGORITHM FOR THE IDENTIFICATION OF ANALOGOUS OBJECTS IN CARBONATE RESERVOIRS OF THE VOLGA-URAL OIL AND GAS PROVINCE

For the conditions of deposits confined to the carbonate reservoirs of the Volga-Ural oil and gas province, an algorithm for searching for analogous objects based on the identification procedure is proposed. The principal boundaries of the search for analogous objects confined to various stratigraphic systems have been established through a comprehensive analysis of geological and commercial data. The significant influence of tectonic confinement on the formation of the features of the geological structure of deposits and their distribution in the axes of canonical discriminant functions is shown. The presence of uncertainty in the separation of objects using the tectonic factor is explained by the similarity of objects in the marginal zones of adjacent tectonic elements in both terrigenous and carbonate reservoirs, which in turn must be taken into account when implementing key aspects of field development design. During the simulation, a certain similarity of individual deposits in the carbonate reservoirs of the carboniferous system was established, confined not only to various tectonic elements, but also to various stratigraphic complexes, which makes it possible to expand the search for analogous objects and the possibility of solving various development management tasks in conditions of deterioration of the structure of oil reserves and low technical and technological indicators of well operation. When using pattern recognition methods, in particular, discriminant analysis, dependencies were obtained that make it possible to successfully adapt the accumulated experience of developing an object to other objects while maintaining a high level of compliance with the logical aspects of hydrodynamics and physics of reservoir systems. Further development of the algorithm presented in the work lies in the plane of using a minimum number of parameters for analysis, ensuring a high percentage of separation of objects, taking into account the heterogeneity of their values.

Factor analysis-based deep differentiation of oil deposits in the Ural-Volga region

The purpose of the article is to present an algorithm developed on the scientific and methodological foundations of quantitative and qualitative processing of geological and commercial data to implement the procedure for deep identification of deposits. The developed algorithm consists of two levels: the initial stage includes facility identification by tectonic and stratigraphic characteristics resulting in the formation of a number of megagroups of objects. Then they are subjected to deep differentiation using the elements of data factor analysis, which is carried out together with the monitoring of the highly identical objects. The presented approach to solving the problems of field effective grouping is the most effective due to a comprehensive and reasonable assessment of the groups of facilities formed as a result of modeling. The developed algorithm was tested on example of a number of fields associated with terrigenous reservoirs of the Devonian and carboniferous systems of the Volga-Ural oil and gas province. After two calculation stages the percentage of correctly grouped objects averaged 96.8 %, which is a high result. To make the search for analogous objects qualitative and objective eighteen equations have been obtained that combine twenty parameters describing the geological and physical characteristics of productive formations as well as the physico-chemical properties of the fluids saturating them at the sufficient level of reliability. Based on the results of using the developed algorithm for deep identification of deposits, the authors obtained a number of relevant mathematical dependencies between various parameters, graphical distributions of objects in the axes of the main components, which all together enable efficient and systematic search for analogous objects in the deposits of terrigenous reservoirs of the Devonian and carboniferous systems of the Volga-Ural oil and gas province. Besides, the presented identification diagrams enable successful management of the processes of oil recovery within the micro- and macro-levels of facility distribution in the axes of the main components. They also allow to form a list of general recommendations that will contribute to the optimal development of liquid hydrocarbon resources.

The role and significance of the tectonic-stratigraphic factor in the formation of the structural features of hydrocarbon deposits of the Volga-Ural oil and gas province

The article establishes the role and importance of the tectonic-stratigraphic factor in the formation of the structural features of hydrocarbon deposits in the Volga-Ural oil and gas province. It has been established that the type of reservoir, tectonic and stratigraphic confinement of the objects of study determine the geological and physical features of the deposits by more than two thirds and are the basis for the identification of objects at a qualitative level. An algorithm is proposed for selecting analogous objects at a qualitative level for deposits emerging from exploration in the absence of representative data on the geological, physical and physico-chemical properties of formations and fluids based on its belonging to a stratigraphic system, tier, horizon, tectonic element. Keywords: tectonics; stratigraphy; analog objects; identification; image recognition.

Refining solutions of development problems of the Volga-Ural oil and gas province fields using geological and statistical model ranking methods

The purpose of the present research is to provide a comprehensive analysis of data on the geological and physical properties of formations and the fluids saturating them in the Volga-Ural oil and gas province using the methods of geological and statistical model ranking. The discriminant analysis conducted on the basis of qualitative criteria (reservoir type and stratigraphic confinement) identified in all cases the zones of uncertainty, which affect the effectiveness of managerial decision-making in the conditions of analog objects. On this score, the results for six models were refined and updated according to the principle of rank uniqueness value calculation by three methods, both for each model individually and for model systems while using them within the obtained distributions of objects in the axes of canonical discriminant functions. Theoretical and practical recommendations were given regarding the use of geological and statistical models in the development of Volga-Ural oil and gas province fields. The results obtained can be used to solve a wide range of practical problems of proactive resource management, which enable effective determination of the best strategy for the successful extraction of residual and hard-to-recover oil reserves. The proposed parameter ranking table allows both to determine the most unstable parameters with a high degree of probability and to level the factor of heterogeneity and disequilibrium of field data. The conducted study established that identification of object association with a particular group in the axes of canonical discriminant functions leads to the formation of the zone of uncertainty. The latter increases the risks of making ineffective managerial decisions when developing different categories of subsoil users’ assets. Using the methods of ranking geological and statistical models, an algorithm for constructing a hierarchical system is proposed, which allows to expand the application field of the results of geological and statistical modeling in the oil and gas industry as well as to reduce the risk of nonrepresentative results.

Choosing well grid density for low productivity carbonate reservoirs

Based on the analysis and generalization of the experience in developing various groups of low-productivity deposits in the carbonate reservoirs of the Volga-Ural oil and gas province, the article proposes geological and statistical dependencies that allow for a differentiated choice of grid density for wells both between selected groups of objects and within them, depending on the geological characteristics. Technical and economic calculations determined the drilling zones and helped select an optimal well grid density. Calculations were made using geological and commercial data on sufficiently studied deposits, which are currently in the final stage of operation. The results presented in this paper allow us to solve a wide range of field development tasks in order to extract residual oil reserves by drilling new wells with an individual design at each facility or drilling side shafts.

Using microbiological technology to increase oil recovery for terrigenous oil deposits

In this paper, the authors consider one of the widely used methods to increase the efficiency of flooding within the terrigenous reservoirs of the Volga-Ural oil and gas province - microbiological effects on the matrix of rocks to align the profile of pick-up and production. The process of the influence of metabolic products produced by microorganisms on the change in oil recovery coefficients over time has been comprehensively studied, as a result of which a significant increase in oil mobility has been established. The results of the measures and their main technical and economic indicators before the impact and after the operation are presented, on the basis of which it is recommended to use this technology to increase the efficiency of oil displacement in fields at the final stage of development as one of the alternative options for implementing high-quality energy resource management.

Visean terrigenous sediments of the South Tatar Arch (Volga-Urals oil and gas bearing province) – multifacial filling of the karst surface of the Tournaisian isolated carbonate platform

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, well-sorted 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.

Application of inflow control devices in the development of oil deposits of terrigenous reservoirs at a late stage of development

The article presents the results of experimental application of autonomous-type inflow control devices in conditions of a terrigenous reservoir with the presence of oil and water zones. Conceptual approaches to modeling the completion design when making decisions about development with the installation of inflow control are reflected. The problems of premature watering of wells, including horizontal ones, are shown. According to the results of the application of the inflow control unit on the layers of the Bobrikovsko-Radaevsky horizon, the positive potential of widespread introduction on waterfowl-type reservoirs has been confirmed. The recommendations on the need for further search for the optimal finishing design are substantiated. The high practical significance of the devices considered by the authors for implementation in the fields of the Volga-Ural oil and gas province with similar geological and physical characteristics, including for terrigenous objects, is noted. Keywords: inflow control devices; terrigenous collector; horizontal borehole; watering; cone formation; plantar water; displacement characteristics.

Improving the efficiency of reservoir pressure monitoring in low-permeable carbonate reservoirs

he modern development of the resource base of the Volga-Ural oil and gas province is characterized by a reduction in the share of highly productive development facilities. The emphasis is shifting towards the operation of low-productivity collectors. Improving the efficiency of managing such assets requires timely monitoring of the energy state of deposits, reasonable selection of geological and technological measures. The approach to monitoring reservoir pressure in this case should differ from the standard, a combination of the most effective research methods is necessary. In conditions of low productivity, methods based on long-term monitoring of reservoir pressure with subsequent data processing using special techniques have proven themselves well. Ultimately, the combination of various methods for monitoring the energy state of low-yielding carbonate reservoirs allows you to individually create an effective research program that allows you to further manage the development. The presented article is devoted to solving these problems. Keywords: carbonate reservoir; permeability; pressure recovery curve; thermomanometric systems; multi-well retrospective test; control piezometric well stock.

Geological Filtration Model of the Layers of Nizovsky Field of Volga-Ural Oil and Gas Province

The article presents the results of modeling a three-dimensional digital geological filtration model. The substantiation of the volumetric grids of the model is given and the analysis of the distribution of filtration-capacitance properties of layers and models of reservoir saturation with fluids is carried out. Based on the constructed three-dimensional model of Nizovsky field, the reliability of revealing hydrocarbon reserves at the field has been confirmed.

Technique and results of determination of vertical variations in rock thermal properties, temperature gradient and heat flow

The paper describes the results of experimental geothermal studies of the formation surrounding Savitskaya-300 well (depth 3555 m) drilled in the Volga-Ural oil and gas basin (Orenburg region, Russia). The work was aimed, firstly, at obtaining geothermal data for basin modeling and, secondly, at improving the instrumental and methodological foundations of experimental studies. Continuous core profiling of the rock thermal conductivity, volumetric heat capacity, and thermal anisotropy was performed on all 2886 recovered core samples with the total length of 329.1 m. Additional measurements were conducted at fluid saturation and elevated temperatures. For non-cored intervals, the rock thermal properties were determined from well-logging data and via measurements on rock cuttings. The studied formation is characterized by high thermal heterogeneity at both the level of strata (horizons) and individual samples. Significant thermal anisotropy up to 1.50–1.66 in the lower part of the well has been observed. To obtain data on vertical variations of equilibrium temperature and its gradient, temperature logging was performed 7 times within the 2 to 186 days of well shut-in. New data on the recovery of temperature and its gradient after drilling are important for the practice of applied and fundamental geothermal surveys. A significant increase in heat flow with depth was established based on the results of temperature gradient and rock thermal conductivity determination for 34 depth intervals. The observed general vertical variation in the whole depth range of the well up to ∼3.3 km depth can be attributed to paleoclimatic effect in the Late Pleistocene-Holocene, while the sharp increase in heat flow at ∼3.3 km within Fransian sediments is possibly due to advective heat transfer by fluid filtration. The apparent heat flow was established to be 84.3 mW⋅m−2 in the lower section of the well, below 3.3 km. The value may be close to the steady-state heat flow value, which is 84% higher than the previous published average data for the studied area.

A brief history of the oil and gas potential of the Volga-Ural basin. A View from the 21st Century

The article presents data on the history of the discovery of oil and gas deposits within the central and northern parts of the Volga-Ural oil and gas basin. On the basis of published scientific and stock literature, the evolution of geological thought on the issue of identifying oil sources is traced. A special role is assigned to the history of studying the geological structure and oil and gas potential of the Riphean-Vendian (Precambrian) complex. The work contains data on scientific schools of the past and present.

Using the method of analogies to increase the further development efficiency of the Devonian productive facilities of the Tuymazy and Bavly oil fields

The authors of the article, in order to widely use the successful experience of applying technologies for the further «mature» oil fields of the Volga-Ural oil and gas province (VUOGP) development and reducing the risks of making low-efficiency decisions, propose to combine fields into groups based on the use of factor analysis. The results of formation groups associated with various stratigraphic elements within the Tuymazinsky and Bavlinskoye oil fields identification are presented. The cross-use of technologies that have shown their effectiveness in the residual reserves’ development is proposed. The features of the geological-physical and physical and chemical properties of the layers and the saturating them fluids within the facility groups for successful technologies replication at the VUOGP deposits are highlighted. Keywords: carbonate and terrigenous deposits; residual oil reserves; geological and physical; factor analysis; analogy method; risk reduction.

Development of methods for increasing oil recovery of hard-to-recover reserves of the Romashkinskoe field

The article discusses the method of petrophysical research, which was developed at the beginning of the XXI century. The study provides data related to the study of the Volga–Ural oil and gas province. Using the example of the Romashkinskoe field, it is shown how the use of petrophysical characteristics made it possible to clarify the interpretation of geophysical studies of wells. The conclusion is made about the relevance of using this method in analyzing the state of mineral reserves in the deposits of the Volga-Ural province.

The Deep Structure of the Proterozoic Complex of the Sedimentary Cover of the East European Platform: Oil and Gas Potential

The article considers the features of the geological structure and formation of the sedimentary Proterozoic complex. It is shown that the Upper Precambrian deposits on ancient platforms are thick, have similar sedimentation conditions, and are characterized by the presence of oil and gas source strata with high generation potential and the presence of large deposits. The authors scrutinized the main trends and identified the regularities of the geological structure of the Riphean‒Vendian complex of the European part of Russia. Riphean‒Vendian sedimentary deposits are widespread on the East European Platform and fill extensive rift-aulacogen depressions. The largest depressions are the Kamsko-Belsky trough, which is the main zone of Riphean sedimentation in the Volga‒Ural oil and gas province (OGP), the Vychegodsky trough in the Mezen syneclise, and the Pachelma and Central Russian aulacogenes in the Moscow syneclise. The authors performed mathematical processing of materials on the geological structure of the basement surface and Riphean‒Vendian deposits of the Volga‒Ural oil and gas province, which made it possible to establish statistically significant relationships with the ancient basement and regularities in the structure of sedimentary strata. On the territory of the European part of Russia in the Riphean‒Vendian deposits, industrial and non-industrial oil inflows, oil and gas occurrences of various intensity were recorded at various stratigraphic levels, have been established.