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Date submitted2024-05-15
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Date accepted2025-01-28
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Date published2025-04-30
Study of changes in the void space of core samples under cyclic loading
The subsurface state is explored and analysed by studying the core material. This is the basis for forecasts, construction and improvement of models. The reservoir properties of rocks obtained from the laboratory study of sample are subject to a system error caused by three main factors: rock selection in the zone of altered stress-strain state, rock removal from the thermobaric conditions of natural occurrence, and the measuring equipment error. A change in the natural stress-strain state of rocks occurs as a result of intervention in the formation system and the entire massif by constructing a well, creating overburden and depression. The rise of the core causes unloading from formation pressure to atmospheric one, natural saturation is lost, temperature conditions change. This affects the reservoir properties and rock injectivity. This study is aimed at investigating changes in the void space of the rock in formation conditions under cyclic loading. Based on the data obtained, a regression forecast of properties is made, excluding external influences. The article describes the results of experiments on multiple loading and unloading of water-saturated sandstone samples by geostatic pressure with precise control of the water displaced and returned to the void space. This method enables us to record the change in the internal void volume of the rock and, as a consequence, elastic and plastic deformations, the value of relaxation of elastic deformations. The dynamics of change in the coefficients of porosity and compressibility from the stress state cycle is estimated and the range of predicted porosity values of the rock in formation conditions is determined. For samples of permeable medium- to fine-grained sandstone, the obtained character of porosity change gives a forecast of the initial porosity in formation conditions of 20.19±0.61 %. Thus, the exclusion of human impact on porosity gives values 1.42 % higher than the results of standard laboratory studies.
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Date submitted2023-06-25
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Date accepted2024-11-07
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Date published2025-02-25
Study of wormhole channel formation resulting from hydrochloric acid treatment in complex-type reservoirs using filtration and X-ray computed tomography methods
- Authors:
- Andrei A. Аbrosimov
The primary function of hydrochloric acid treatment (HAT) is to create the maximum number of high-conductivity channels in the near-wellbore zone of the reservoir to restore its permeability and enhance hydraulic connectivity between the undisturbed part of the formation and the well. The objective of this study is to physically model HAT on core samples from the Orenburg oil and gas condensate field and to research the impact of such treatment on the structure of the pore space of rocks related to complex-type reservoirs. The complexity of the rock's pore space and the low permeability of the formations are distinguishing features of the study object. For this reason, HAT is a widely applied method for production intensification, necessitating the verification of acid injection rates, where the success criterion is the formation of high-conductivity filtration channels (wormholes) in the near-wellbore zone. These channels significantly expand the drainage area of wells, thereby bringing additional reservoir sections into development. The study examined the characteristics of filtration channel development resulting from acid treatment. Their structure was characterized and analyzed using X-ray computed tomography. The complex study confirmed the accuracy of the selected injection rate and provided practical recommendations for enhancing the efficiency of HAT.
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Date submitted2023-07-04
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Date accepted2024-05-02
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Date published2025-02-25
Study of the pore structure in granite and gabbrodolerite crushed stone grains of various sizes
- Authors:
- Elena E. Kameneva
- Viktoriya S. Nikiforova
The results of a study on the pore structure of crushed stone grains of various sizes, obtained through staged disintegration of gabbrodolerite and microcline granite – rocks differing in texture, structure, and mineral composition – are presented. Research conducted using X-ray computed microtomography revealed that disintegration leads to changes in the pore structure of the rocks. The increase in overall porosity and pore concentration in the crushed stone grains is associated with the formation of newly developed pores of various sizes and sphericity. A clear relationship between the porosity of the crushed stone grains and their size is absent, which is due to the textural and structural characteristics as well as the mineral composition of the original rocks. The scale factor is evident only in the case of gabbrodolerite, which is characterized by a fine-grained structure, massive texture, and stable mineral composition. Fine gabbrodolerite grains exhibit lower pore concentration compared to larger grains, which aligns with the statistical theory of rock strength, according to which the probability of defects (pores and microcracks) decreases as the sample size diminishes – the smaller the grain size, the higher its strength. In contrast, for porphyritic granites with an uneven grain size, the trend is reversed – smaller grains are more porous. A study of the porosity of individual rock-forming minerals in granite showed that pores are unevenly distributed in the granite crushed stone grains. The highest concentration of pores is typical for microcline. The presence of brittle and porous microcline inclusions in the granite crushed stone grains leads to the formation of new pores and microcracks, whose number increases with the repeated application of load during staged disintegration.
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Date submitted2022-08-20
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Date accepted2022-11-17
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Date published2022-12-29
Comparison of the approaches to assessing the compressibility of the pore space
- Authors:
- Vitaly S. Zhukov
- Yuri O. Kuzmin
Integral and differential approaches to determining the volumetric compression of rocks caused by changes in the stress state are considered. Changes in the volume of the pore space of rocks are analyzed with an increase in its all-round compression. Estimation of changes in the compressibility coefficients of reservoirs due to the development of fields is an urgent problem, since the spread in the values of compressibility factors reduces the adequacy of estimates of changes in the physical properties and subsidence of the earth's surface of developed fields and underground gas storages. This parameter is key in assessing the geodynamic consequences of the long-term development of hydrocarbon deposits and the operation of underground gas storage facilities. Approaches to the assessment differ in the use of cumulative (integral) or local (differential) changes in porosity with a change in effective pressure. It is shown that the coefficient of volumetric compressibility of pores calculated by the integral approach significantly exceeds its value calculated by the differential approach, which is due to the accumulative nature of pore compression with an increase in effective pressure. It is shown that the differential approach more accurately determines the value of the pore compressibility coefficient, since it takes into account in more detail the features of the change in effective pressure.
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Date submitted2021-05-31
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Date accepted2021-10-18
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Date published2021-12-16
Experimental evaluation of compressibility coefficients for fractures and intergranular pores of an oil and gas reservoir
- Authors:
- Vitaly S. Zhukov
- Yuri O. Kuzmin
The paper is devoted to studies of the volumetric response of rocks caused by changes in their stress state. Changes in the volume of fracture and intergranular components of the pore space based on measurements of the volume of pore fluid extruded from a rock sample with an increase in its all-round compression have been experimentally obtained and analyzed. Determination of the fracture and intergranular porosity components is based on the authors' earlier proposed method of their calculation using the values of longitudinal wave velocity and total porosity. The results of experimental and analytical studies of changes in porosity and its two components (intergranular and fractured) under the action of effective stresses are considered. This approach allowed the authors to estimate the magnitude of the range of changes in the volumetric compressibility of both intergranular pores and fractures in a representative collection of 37 samples of the Vendian-age sand reservoir of the Chayanda field. The method of separate estimation of the compressibility coefficients of fractures and intergranular pores is proposed, their values and dependence on the effective pressure are experimentally obtained. It is determined that the knowledge of the values of fracture and intergranular porosity volumetric compressibility will increase the reliability of estimates of changes in petrophysical parameters of oil and gas reservoirs caused by changes in the stress state during the development of hydrocarbon fields.
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Date submitted2020-05-05
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Date accepted2020-10-05
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Date published2020-11-24
Assessment of the Influence of Water Saturation and Capillary Pressure Gradients on Size Formation of Two-Phase Filtration Zone in Compressed Low-Permeable Reservoir
The paper examines the influence of capillary pressure and water saturation ratio gradients on the size of the two-phase filtration zone during flooding of a low-permeable reservoir. Variations of water saturation ratio s in the zone of two-phase filtration are associated with the pressure variation of water injected into the reservoir; moreover the law of variation of water saturation ratio s ( r , t ) must correspond to the variation of injection pressure, i.e. it must be described by the same functions, as the functions of water pressure variation, but be subject to its own boundary conditions. The paper considers five options of s ( r , t ) dependency on time and coordinates. In order to estimate the influence of formation and fluid compressibility, the authors examine Rapoport – Lis model for incompressible media with a violated lower limit for Darcy’s law application and a time-dependent radius of oil displacement by water. When the lower limit for Darcy’s law application is violated, the radius of the displacement front depends on the value of capillary pressure gradient and the assignment of s function. It is shown that displacement front radii contain coefficients that carry information about physical properties of the reservoir and the displacement fluid. A comparison of two-phase filtration radii for incompressible and compressible reservoirs is performed. The influence of capillary pressure gradient and functional dependencies of water saturation ratio on oil displacement in low-permeable reservoirs is assessed. It is identified that capillary pressure gradient has practically no effect on the size of the two-phase filtration zone and the share of water in the arbitrary point of the formation, whereas the variation of water saturation ratio and reservoir compressibility exert a significant influence thereupon.
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Date submitted2019-12-25
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Date accepted2020-06-30
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Date published2020-10-08
Accounting of geomechanical layer properties in multi-layer oil field development
Amid the ever-increasing urgency to develop oil fields with complex mining and geological conditions and low-efficiency reservoirs, in the process of structurally complex reservoir exploitation a number of problems arise, which are associated with the impact of layer fractures on filtration processes, significant heterogeneity of the structure, variability of stress-strain states of the rock mass, etc. Hence an important task in production engineering of such fields is a comprehensive accounting of their complex geology. In order to solve such problems, the authors suggest a methodological approach, which provides for a more reliable forecast of changes in reservoir pressure when constructing a geological and hydrodynamic model of a multi-layer field. Another relevant issue in the forecasting of performance parameters is accounting of rock compressibility and its impact on absolute permeability, which is the main factor defining the law of fluid filtration in the productive layer. The paper contains analysis of complex geology of a multi-layer formation at the Alpha field, results of compression test for 178 standard core samples, obtained dependencies between compressibility factor and porosity of each layer. By means of multiple regression, dependencies between permeability and a range of parameters (porosity, density, calcite and dolomite content, compressibility) were obtained, which allowed to take into account the impact of secondary processes on the formation of absolute permeability. At the final stage, efficiency of the proposed methodological approach for construction of a geological and hydrodynamic model of an oil field was assessed. An enhancement in the quality of well-by-well adaptation of main performance parameters, as well as an improvement in predictive ability of the adjusted model, was identified.
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Date submitted2018-11-03
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Date accepted2019-01-16
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Date published2019-04-23
Interpretation of the tracer investigation results considering convective mass transfer
- Authors:
- V. A. Korotenko
- S. I. Grachev
- A. B. Kryakvin
The paper discusses the results of interpreting well tracer studies. It is shown that from the law of mass conservation it follows that when filtering a volume of an indicator, part of the injected tracer flows into the matrix. With the flow of fluid containing the indicator from the low-filtration resistance channel (LFR) into the surrounding matrix, the linear dimensions of the flow area depend on the permeability and porosity properties of the high-permeability channel and the matrix. While another part of the tracer moves toward the production well, its mass is lost due to diffusion processes. From the solution of the diffusion equation, it follows that the initial concentration of the tracer decreases in the course of filtration along the LFR channel. To interpret the results of the tracer studies, different cases of the LFR channels' location in the volume of the productive formation are considered. The varied parameter w allows characterizing the presence of several peaks in the concentration of the indicator and calculation the filtration parameters of the LFR channels. Depending on the known technological indices, several methods for determining pore volumes in the LFR channels have been proposed. To reduce the water cut in producing wells and to apply the technology of changing or aligning the injectivity profiles, calculations of the pore channels' radii in the mass of highly permeable seams are presented. It is shown that the volume of the chemical reagent pumped into the injection well to isolate the LFR channel is affected by the linear dimensions of the drainage area for the aqueous solution of indicator. Examples of the calculation for the permeability and porosity parameters of the LFR, the volume of pore channels necessary to isolate water inflow, and the radii of pore filtration channels, which influence the selection of the size of chemical reagent molecules, are given.
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Date submitted2013-07-27
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Date accepted2013-09-21
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Date published2014-03-17
Development free-chemical metod of cltaning water out from oil on the cmf companies
- Authors:
- M. A. Pashkevich
- I. A. Golubev
In this paper deals with the problem of pollution of oil-contaminated wastewater. A method of treatment which increases the quality of recyclable waste water, by improving existing production systems using Reagent-free method.
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Date submitted2009-08-05
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Date accepted2009-10-26
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Date published2010-02-01
The influence of change in geotechnical engineering and geoenvironmental conditions during the process of building and operation of constructions of projected Alekseevsky cement factory on their stability (Mordovia Republic)
- Authors:
- K. V. Pankratova
The influence of change engineering-geological and geoenvironmental conditions on stability of cement factory are considered in this paper. Influence of additional humidifying, rise in temperature in the basis of constructions and activization of microbic activity is considered. The specificity of physicomechanical properties of silica rock and upper Jurassic clay is considered. Results of experimental researches of increase in microbic mass in soils at watering and heating are resulted. The estimation influences of temperature on deformation ability soils is given.
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Date submitted2008-10-16
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Date accepted2008-12-10
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Date published2009-12-11
Collecting properties of rocks in changes оf stress state type
- Authors:
- A. T. Karmansky
The article presents the results of investigations of the influence of stress state form, cyclic loading and time of bearing specimens under loads on the pattern of changes in porosity and permeability. It was stated that compressibility of rocks is proportional to porosity, and with rise of applied stress the compressibility decreases exponentially.
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Date submitted2008-10-22
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Date accepted2008-12-15
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Date published2009-12-11
Regularities of changes in strength of rocks under complicated stress state, different levels of humidity and pore pressure
- Authors:
- A. T. Karmansky
The conducted investigations allowed to establish the regularities of changes in mechanical properties of rocks with due account of influence of the stress state type, forms and kinds of moisture in rocks. Condition of the final state may be regarded as the criterion of rock failure depending on the moisture content, value of pore pressure and stress state type under constant velocity of deformation.