Increase Of Confining Pressure Research Articles

Failure behaviour and damage evolution of multi-recycled aggregate concrete under triaxial compression

In this paper, the stress–strain behaviour, mechanical properties, characteristic stress, and damage evolution of multi-recycled aggregate concrete (Multi-RAC up to 3 recycling cycles) under triaxial compression were investigated, considering the effects of confining pressure and number of recycling cycles. Furthermore, a parametric sensitivity evaluation of key parameters using grey correlation theory to analyse the peak stress, peak strain, and elastic modulus of Multi-RAC. The results indicate that both peak stress and peak strain increase with rising lateral confining pressure. While the peak stress of Multi-RAC is lower than that of natural aggregate concrete (NAC), the deformation capacity of Multi-RAC is greater. The deformation and failure of Multi-RAC under triaxial loading can be categorized into five stages. Notably, crack initiation stress (σci) and crack expansion stress (σcd) demonstrate nonlinear growth as lateral confining pressure increases. In particular, the second generation of Multi-RAC (RACII) exhibits superior performance in resisting crack initiation and expansion, while the third generation of Multi-RAC (RACIII) performs relatively less favourably. The energy evolution characteristics and division of failure stages of Multi-RAC are effectively characterized by the evolution of elastic strain energy (Ue) and dissipation energy (Ud). The degree of progressive damage aligns with the increase in dissipation energy. Among the five key parameters, the number of recycling cycles shows the most significant grey correlation effect on the peak stress, peak strain, and elastic modulus of Multi-RAC. These findings contribute to a deeper understanding of the mechanical properties and failure behaviours of Multi-RAC under the complex triaxial loading conditions, thus promoting the application of Multi-RAC as a structural concrete.

Triaxial compression test of coarse-grained soil in waste dump under different consolidation stresses conditions

In order to explore the mechanical response characteristics of coarse-grained soil in waste dump under different consolidation stress conditions, the isobaric consolidation drained triaxial test and K0 consolidation drainage triaxial test under different confining pressures are performed, and the test data of stress-strain and volume deformation of soil are compared and analysed. The results show that the initial stress of soil under K0 consolidation condition is not zero. The shear stress-strain curves of soil with different consolidation conditions show hardening characteristics. When confining pressure increases, the shear stress of isobaric consolidated soil increases rapidly, and its failure shear stress increases significantly compared with K0 consolidated soil. Shear expansion of coarse-grained soil under low confining pressure and shear shrinkage under high confining pressure. Under low confining pressure, K0 consolidated soil is more prone to shear expansion, and the amount of shear expansion is greater than that of isobaric consolidated soil. Under medium and high confining pressure, the volume compression change of isobaric consolidated soil is greater than that of K0 consolidated soil. The initial tangent Poisson’s ratio of coarse-grained soil under different consolidation stress conditions decreases with the increase of confining pressure, and changes in a power function with the confining pressure. The cohesion of soil under isobaric consolidation stress condition, while the difference of internal friction angle of soil under different consolidation stress condition is small. The strength and deformation characteristics of soil are closely related to the initial stress state of soil. The triaxial test is used to obtain the shear strength index of soil, and the isobaric consolidation condition should not be used instead of K0 consolidation condition.

Modelling crack behavior of granite using multiscale grain-based model

Understanding the macroscopic and microscopic failure process of brittle rocks is helpful to predict the strength and deformation characteristics. However, the brittle rock is a typical heterogeneous material, and it is difficult to study the evolution mechanism of microcracks at the grain scale through laboratory tests. In this study, we propose a multiscale grain-based model based on FDEM, which can consider the actual grain size and the inter-grain and intra-grain contacts of diverse minerals. Most importantly, it can explicitly characterize local polycrystal inclusions and internal cleavage of some mineral grains. Based on the laboratory test data, a series of simulated tests were conducted, including uniaxial tensile tests, uniaxial compression tests, and conventional triaxial compression tests. The results reveal the importance of transgranular fracture capacity in the simulation of mesoscopic fracture. The failure mechanism of rock samples is controlled by the difference between inter-grain and intra-grain tensile strength under uniaxial compression condition. As the confining pressure increases, the tension failure mechanism is transformed into the shear failure mechanism, indicating a gradual change in rock properties from brittleness to ductility. The ability of mineral to absorb elastic strain energy will significantly affect the microcrack path. Under uniaxial tensile condition, the macroscopic failure results from multiple microcracks, and the intergranular tensile cracks are dominated. In addition, the cleavage planes will provide optimal paths for the propagation of microcracks. The results can help us to understand the mechanism of microcrack evolution in heterogeneous rock, and provide a method for comprehensive analysis of crack propagation and energy evolution.

Numerical Analysis of Cyclic Impact Damage Evolution of Rock Materials under Confining Pressure

To study the effect of cyclic impacts and confining pressure on the damage evolution of rock materials, numerical simulations of cyclic impact tests on rock materials under confining pressure were carried out by LS-DYNA using dynamic relaxation and full restart analysis. The static confining pressure was applied by dynamic relaxation, and cyclic impacts were realized by full restart analysis. As the crack generation and propagation result in the failure of elements in the finite element model, the damage variable defined by the crack density method was characterized by volume reduction. Numerical simulation indicates that both the confining pressure and amplitude of incident stress waves significantly affect the damage evolution of rock materials. High incident stress waves lead to severe damage, while large confining pressure results in minor damage. Under confining pressure, the damage to rock materials is alleviated due to the constraint effect on crack propagation. The number of cyclic impacts before macroscopic fracture increases as the confining pressure increases and decreases when the amplitude of the incident stress waves increases. The cumulative damage of rock materials under confining pressure progressively increases with the number of cyclic impacts, and the damage evolution exhibits three distinct stages: rapid rising, steady development, and sharp rising.

Experimental investigation on fracturing effects in hydraulic sand fracturing with acoustic emission and 3d laser scanning

Due to the extremely low permeability of shale reservoirs, large-scale reservoir fracturing is required. Hydraulic fracturing is one of the most important technologies in shale gas exploration and development. In this paper, the acoustic emission energy and the number of location and fracture surface morphology of specimens before and after fracture are studied through hydraulic sand fracturing test. The test results show that: (1) the energy ratio obtained during hydraulic fracturing without proppant is the smallest, and increasing the confining pressure, as well as reducing the displacement and viscosity of the fracturing fluid will cause the energy ratio to decrease. From the perspective of acoustic emission energy, the proppant play an important role in the generation of fractures during hydraulic sand fracturing; (2) when the confining pressure increases, the number of shale specimens before and after rupture is the largest, but the total number of locating events is smaller than the sanding ratio increased; there is no proppant hydraulic fracturing, the number of specimens before and after the rupture is the largest. And the total number reached the minimum, indicating that the proppant can play an important role in the hydraulic sand fracturing test; (3) the sand is relatively large, the specific surface and standard deviation both reach the maximum, indicating that the fracture surface roughness is the largest under the test condition, and the fracturing effect is the best, but the specific surface and standard deviation are the minimum when fracturing without proppant, so indicating that the fracture surface fracturing effect is the worst at this time.

Determination of Dynamic Properties of Fine-Grained Soils at High Cyclic Strains

Shear modulus (SM) and damping ratio (DR) are significant in seismic design and the performance of geotechnical systems. The evaluation of soil reactions to dynamic loads, such as earthquakes, blasts, train, and traffic vibrations, necessitates the estimation of dynamic SM and DR. The aim of this research is to determine the cyclic parameters of unsaturated soils in and around Peshawar, and how these properties depend upon the varied confining pressures and shear strains. Undisturbed samples were collected using Shelby tubes from five boreholes at different locations along Jamrud Road, Peshawar. The index properties (grain size distribution, plasticity index, and specific gravity) and dynamic properties of these samples were determined. Three samples of 100 mm in height and 50 mm in diameter were obtained from each Shelby tube. After preparing and mounting the sample in the triaxial cell, the sample is first saturated by increasing the cell and back pressures in increments of 50 kPa until the value of Skempton’s pore pressure parameter (B) reaches ≥ 0.96. Samples were consolidated at confining pressures of 150, 200, and 300 kPa, then subjected to cyclic shear strains of 0.2, 1, 2, 2.5, and 5%. Shear stress–strain hysteresis loops were plotted, and the values of SM and DR were calculated for each cycle. Generally, at shear strains of 0.2 and 1%, the slope of the loops is steep, and gradually becomes gentler at higher strains of 2, 2.5, and 5%. It is found that, with an increasing number of cycles, the SM and DR decrease. The SM decreases with increasing shear strain, whereas the DR increases at shear strains of 0.2–1%, then decreases for strains of 2, 2.5, and 5%. The confining pressure has more influence at a shear strain of 0.2–1%, while little effect has been observed at a shear strain of 2.2–5%. The values of SM are higher at higher confining pressures at a given shear strain. The results show higher stress values during the initial cycles because of the greater effective stress that developed in response to shear strain while, with an increase in the number of cycles, the pore water pressure gradually increases, thereby reducing the effective stress and weakening the bonds between soil particles. In dynamics, when the confining pressure increases, particles are closer to contact, so the travel paths of waves increase. The energy loss will increase, so DR will decrease.

Study on mechanical properties and fracture modes of sandstone with cracks under triaxial compression

AbstractThis study examines the mechanical properties and fracture modes of sandstone with single and double cracks under varying confining pressures through triaxial compression tests. The stress–strain curves, mechanical parameters, and fracture modes of both intact and cracked sandstone are analyzed based on experimental results. The study finds that the presence of cracks has a significant impact on the mechanical properties of sandstone, with greater damage observed with an increase in the number of cracks. The peak strength and strain of a cracked rock sample increase with the increase in crack angle. The fracture mode of sandstone is influenced by both crack angle and confining pressure. When the crack angle is small, the fracture mode is a combination of shear and tensile failure, while a large crack angle results in shear failure. Moreover, as the confining pressure increases, the degree of damage to the sandstone also increases.

Estimation of compliance tensor and anisotropy index for fractured rock masses using field measured data

This paper proposes a method for calculating the fractured rocks compliance matrix using field data. The method is based on the Oda fracture tensor, which combines the mechanical properties of intact rocks and the geometric and mechanical properties of the fractures. The compliance matrix-based anisotropy index EAI is derived to evaluate the anisotropy of the fractured rock mass. The value of EAI ranges from 0 to 1.0986. The closer the EAI value is to 0, the higher the degree of anisotropy. According to the fracture parameters measured in the field, the fracture's normal stiffness and shear stiffness values are derived. Then the compliance matrix of the fracture is determined. In addition, the influence of the confining pressure on the normal and shear stiffness of the fracture was studied. The results show that (1) as the spacing and stiffness ratio of the fracture group increase, the EAI of the corresponding fracture rock increases; (2) as the confining pressure increases, it is necessary to apply greater normal stress to produce the same strain and the elastic modulus increases; (3) the larger the stiffness ratio is, the larger the anisotropy index EAI is at the same confining pressure.

Study on Damage Behavior and Its Energy Distribution of Deep Granite at High-Temperature Conditions

The phenomenon of surrounding rock damage and rupture caused by high temperatures is widespread, and has become a potential threat to the safety of nuclear waste disposal repositories. In order to reveal the energy distribution pattern of fractured granite during the failure process under different confining pressures, triaxial compression tests were carried out on rocks with different initial thermal damage. Firstly, the rock was treated at a high temperature to analyze the change rule of the porosity of the rock after high-temperature treatment, define the equivalent damage coefficient, and analyze the influence of confining pressure and equivalent damage coefficient on the peak stress and peak strain of the rock. The results show that, after high-temperature treatment, the porosity increases with the increase in temperature. The peak stress and corresponding strain of rock samples with similar equivalent damage factors increase with the increase in confining pressure. By comparing the rock samples with the same confining pressure and different initial thermal damage, the larger the confining pressure, the smaller the difference of peak stress of different initial thermal damage specimens. Then, the energy density of rock in a triaxial compression test is quantitatively analyzed by energy theory. The results show that, as long as the confining pressure is the same, the proportion of the dissipated energy of the specimen has a similar evolution trend with the strain. When the confining pressure is the same, the proportion of dissipated energy decreases rapidly with the change of strain due to the increase in equivalent damage factor, but the rate of decline will gradually slow down; however, when the confining pressure increases, the difference caused by the equivalent damage factor will gradually decrease, because the fracture is bound by the confining pressure. Finally, we analyze the maximum dissipated energy during rock deformation and failure. According to the inflection point of maximum dissipated energy, the optimum time for critical support of the key rock mass is determined.

Mechanical properties and influence mechanism of hydroxyl‐terminated polybutadiene propellant under confining pressure

AbstractTo better understand the mechanical properties and influence mechanism of hydroxyl‐terminated polybutadiene (HTPB) propellant under various confining pressures, the uniaxial tension tests with low to medium strain rate and various confining pressures were carried out. The coupling effects of strain rate and confining pressure on mechanical properties were presented. Meanwhile, the confining pressure influence mechanism was analyzed and revealed using the meso numerical simulation method and scanning electron microscopy images of fracture surfaces. The meso damage evolution processes under various confining pressures were presented. The results show that strain rate and confining pressure affect mechanical responses of HTPB propellant significantly. As confining pressure increases, the maximum tension strength and fracture strength increase. The maximum tension strain and failure strain vary slightly with confining pressure under low strain rate, while they increase significantly with confining pressure at medium strain rate. The fracture energy density increases with the increase of strain rate and confining pressure. Meanwhile, the value of saturation pressure depends on strain rate. The confining pressure influence mechanism is to suppress dewetting damage initiation and evolution. Besides, the failure mode of HTPB propellant under different confining pressures is still particles dewetting.

Creep–fatigue mechanical characteristics of salt rocks under triaxial loading: An experimental study

Salt rock is a sedimentary rock that is widely distributed in the crust. Since salt rock has a low permeability, rheological behavior, and self-healing characteristics, it has been extensively exploited for subsurface energy storage and waste disposal. The construction of compressed air energy storage (CAES) facilities using salt caverns for solution mining is a practical solution to achieve carbon peaking and carbon neutrality goals worldwide. The stability of the salt cavern surrounding rock is critical to the function of a CAES plant. Considering the triaxial stress condition of the rock surrounding such underground salt caverns, a number of triaxial creep–fatigue mechanics tests were performed on salt rock using an MTS815 mechanical testing device. The creep–fatigue damage to the salt rock was examined under various confining pressures and stress levels. The main research results and conclusions are as follows. First, the triaxial creep–fatigue stress–strain curves show a similar tendency to classical triaxial fatigue results: the strength and ultimate deformation of salt rocks increase as the confining pressure increases. Second, in contrast to typical fatigue test results, the residual strain before the high-stress plateaus is larger than that after the plateaus during a creep–fatigue test. However, as the confining pressure increases, this disparity decreases. Third, fatigue loading increases creep deformation, and this effect weakens when the confining pressure increases. Fourth, the residual strain differential before and after the high-stress plateau increases together with the stress level, and the contribution of creep strain increases correspondingly. Last, as the confining pressure increases, the salt rock behavior transitions from a brittle response to a fully ductile response. A high confining pressure prevents relative sliding between the salt rock particles. Thus, the effect of confining pressure on the creep–fatigue mechanical behavior of the salt rock reaches a threshold.

Dynamic characteristics and energy evolution of granite subjected to coupled static–cyclic impact loading

In many underground rock projects, rock masses are subjected to coupled static–cyclic dynamic loading. In this paper, dynamic tests were carried out on granite specimens using a modified split Hopkinson pressure bar to study the dynamic characteristics and energy evolution of the rock under coupled static–cyclic impact loading. The results show that both the dynamic characteristics and the energy evolution of granite are sensitive to the number of repeated impacts and the confining pressure. Under the same confining pressure, the dynamic increase factor (DIF), dynamic elastic modulus, and transmitted energy ratio decreases, while the cumulative dissipated energy, cumulative specific energy dissipation and dissipated energy density tend to increase as more impact cycles are applied. The effect of confining pressure on enhancing the mechanical property of the rock is pronounced: the peak stress of rocks under confining pressure during cyclic impact is higher than their quasi-static compressive strength, and the DIF increase as the confining pressure increases. However, its effect on the dynamic elastic modulus is fairly insignificant. The confining pressure could change the crack propagation path of the specimens, and the failure mode is mainly a tensile failure, with no obvious axial splitting. By increasing the confining pressure, the energy dissipation capacity of the rock is significantly improved, and its increased rate of internal damage could be slowed down.Graphical abstract

Combined effects of freeze–thaw cycles and chemical corrosion on triaxial mechanical properties of sandstone

To study the combined effects of freeze–thaw cycles and chemical corrosion on deterioration mechanism of triaxial mechanical properties of sandstone in cold regions, triaxial compression tests were carried out on homologous sandstone specimens after corrosion action of acidic, alkaline or neutral solution and cyclic freeze–thaw action, by taking the pH value of the hydrochemical solution and the number of freeze–thaw cycles as control parameters. The failure mode of triaxial compression is shear-slip failure, and the deviatoric stress–strain curves can be divided into four stages of compaction, linear elastic, yield, and failure. The stress–strain curves and deterioration law of triaxial mechanical properties were analyzed. With the increase of freeze–thaw cycles, the peak stress, peak strain and modulus all decrease, the deterioration degree of the rock specimens increases, and the yield plateau and plastic characteristics in the yield stage become weaker. The strong acid solution shows the largest degree of damage, and the peak stress, peak strain and modulus decreased significantly. The precipitates produced by the reaction between the strong alkaline solution and the specimens adhere to the specimen surface, pores, and fissures, thereby inhibiting further damage and deterioration. Confining pressure is an essential factor affecting the rock mechanical properties. As confining pressure increases, the strength and deformation-resistant ability of specimens increase, and the yield stage on the stress–strain curve is more obvious. The sensitivity of acidic solution to the deterioration of mechanical properties of sandstone is obviously greater than that of alkaline solution. These results provide a theoretical basis for the construction of geotechnical engineering structures in cold regions.

Estimation of mechanics parameters of rock in consideration of confining pressure using monitoring while drilling data

During the drilling process, high-strength rock can lead to various issues such as drilling suppression, bit wear, and increased operational costs. To ensure safe and efficient drilling operations, it is crucial to accurately predict the strength parameters of the rock and recommend modifications to operational procedures. This paper proposes a low-cost and fast measurement method for predicting the strength parameters of rock in the field. To evaluate the effectiveness of this method, a drilling process monitoring experiment was conducted on sandstone, limestone, and granite. The experiment studied the effect of confining pressure on the response of cutting with an impregnated diamond bit. By analyzing the relationship between the thrust force, torque force, and penetration depth under different confining pressures, the researchers developed an analytical model for drilling that considers confining pressure, compressed crushed zone, and bit geometry. The results show that the confining pressure has a significant effect on the cutting response. As the confining pressure increases, the thrust force, torque force, and penetration depth at the cutting point also increase. Furthermore, a new measurement method was proposed to determine the strength parameters, such as cohesion, internal friction angle, and unconfined compressive strength. The estimated strength parameters for the three rock types using the drilling method were in good agreement with those of the standard laboratory test, with an error range of 10%. This method of estimating rock strength parameters is a practical tool for engineers. It can continuously and quickly obtain the drilling parameters of in-situ rocks.

Postcyclic Stiffness Behaviors of Laterite Clay under Various Conditions

The changes in mechanical behaviors of soils after cyclic loading will lead to the generation of additional settlements. The postcyclic stiffness characteristics of soils are usually analyzed by using conventional cyclic triaxial tests, in which only cyclic deviator stress is applied under undrained conditions; however, the cyclic variations of both axial stress and horizontal stress under traffic loading were observed. Moreover, the pore water was permitted to drain under cyclic loading. Therefore, cyclic triaxial tests under partially drained conditions were performed to investigate the postcyclic stiffness characteristics of remolded laterite clay. The influences of variables, such as the cyclic deviator stress, number of cycles, cyclic confining pressure, and degree of reconsolidation, were evaluated. The postcyclic elastic modulus increases as the cyclic deviator stress, number of cycles, and degree of reconsolidation increase, while it decreases as the cyclic confining pressure increases. Nevertheless, the ratio of the postcyclic elastic modulus with and without cyclic confining pressure decreases as the cyclic confining pressure increases; the postcyclic elastic modulus ratio of the degree of reconsolidation to without reconsolidation increases linearly with the increasing degree of reconsolidation. Based on the result, an empirical formula for the postcyclic elastic modulus, considering the effects of both cyclic confining pressure and the degree of reconsolidation, was proposed. The predicted results match the measured data well, indicating that the formula is valid for the prediction of the postcyclic elastic modulus of laterite clays after cyclic loading.

Triaxial Test Study on Energy Evolution of Marble after Thermal Cycle

With the increasing requirements for the exploitation of underground resources, the subject of the physical and mechanical properties of rocks under high temperature and pressure needs to be studied urgently. In order to analyze the mechanical and energy characteristics of rocks under different thermal damages and confining pressures (c), a triaxial compression test is performed on 35 marble samples. The effects of thermal damage and high pressure are simulated with different thermal cycles and confining pressures. The results show that as the number of thermal cycles increases, the peak strain of marble gradually rises, but the peak stress and the elastic modulus (E) decrease by a degree, reaching 11.19‰, 39.53 MPa, 4.79 GPa, while there is no confining pressure applied at eight thermal cycles. At this point, the failure mode gradually changes from brittle fracture to plastic failure. When confining pressure rises, peak stress, peak strain, and elastic modulus all show an upward trend, reaching a maximum of 189.45 MPa, 13.39‰, 35.41 GPa, while the sample is undamaged at 30 MPa confining pressure. Moreover, peak stress increases linearly with confining pressure increase. The increased rate of the peak value of the total absorbed energy, elastic strain energy, and dissipated energy all show a convex trend. The dissipated energy gradually increases with the axial strain (ε1) during the rock loading process. The elastic strain energy has an energy storage limit, but the rock fails when the value exceeds the limit. The limit increases first and then decreases with the number of thermal cycles. These results can provide important engineering references for mining underground resources.

Effects of confining pressure and temperature on strength and deformation behavior of frozen saline silty clay

Buildings are always affected by frost heave and thaw settlement in cold regions, even where saline soil is present. This paper describes the triaxial testing results of frozen silty clay with high salt content and examines the influence of confining pressure and temperature on its mechanical characteristics. Conventional triaxial compression tests were conducted under different confining pressures (0.5–7.0 MPa) and temperatures (−6 °C, −8 °C, −10 °C, and −12 °C). The test results show that when the confining pressure is less than 1 MPa, the frozen saline silty clay is dominated by brittle behavior with the X-shaped dilatancy failure mode. As the confining pressure increases, the sample gradually transitions from brittle to plastic behavior. The strength of frozen saline silty clay rises first and then decreases with increasing confining pressure. The improved Duncan-Chang hyperbolic model can describe the stress-strain relationship of frozen saline silty clay. And the parabolic strength criterion can be used to describe the strength evolution of frozen saline silty clay. The function relation of strength parameters with temperature is obtained by fitting, and the results of the parabolic strength criterion are in good agreement with the experimental results, especially when confining pressure is less than 5 MPa. Therefore, the study has important guiding significance for design and construction when considering high salinity soil as an engineering material in cold regions.

Confining pressure effect on the permeability and mechanical behavior of sandstone under a certain pore water pressure condition

In geotechnical engineering, the mechanical behavior of rocks under various In-situ conditions (stress state including axial stress, confining pressure, pore water pressure) have always been an important topic. Therefore, the confining pressure effect on the permeability and mechanical behavior of different size sandstone samples under a certain pore water pressure condition was studied. The permeability of different sizes samples shows roughly the same exponential de-creasing law with the increase of confining pressure. In the mechanical behavior test, both the loading Young?s modulus E+ and the unloading Young?s modulus E- increased continuously with increasing confining pressure, while the unloading Poisson's ratio m - decreased to a certain value and then remained almost constant.

Hydro-mechanical coupling characteristics and damage constitutive model of low-permeability granite under triaxial compression

To investigate the effect of hydro-mechanical coupling characteristic in low-permeability hard rocks during the excavation of groundwater-sealed energy cavern and hydraulic engineering tunnels or chambers, triaxial compression tests were conducted on engineering granite under different confining and seepage pressures. The mechanical properties, such as the strength and deformation parameters, of granite under hydro-mechanical coupling condition were studied. The permeability of the granite under different stresses first decreases, then stabilizes, and then increases significantly until the final abrupt change, and the inflection point of the abrupt change in permeability tends to be in advance as the confining pressure increases or the seepage pressure decreases. Based on the statistical damage theory and test result, combined with the Mogi-Coulomb strength criterion, a hydro-mechanical coupling statistical damage constitutive model that considers the rock damage threshold and the initial compaction effect was proposed, and the proposed mechanical model was verified based on the test results under different confining and seepage pressures. The proposed mechanical model was further applied to predict permeability catastrophes during rock fracturing and achieves good results. This study provides a theoretical basis for the prevention and control of hydro-mechanical coupled disasters in rock engineering.

Experimental study on the fracture closure law of fault-controlled reservoir

This paper presents the fracture closure law of fault-controlled reservoir under different pressures by means of a combination of laboratory tests and numerical calculation. Fractures are an important seepage channel for fault-controlled reservoirs. With the improvement of the recovery degree of fault-controlled oil and gas reservoirs, the formation pressure decreases, and the effective rock stress increases, which leads to the deformation and even closure of fractures. The dynamic opening and closure of fractures restricts the formation permeability and affects the production of oil and gas wells. In this paper, experimental methods are used to study the fracture closure law. First collect carbonate rock samples, prepare samples through Brazilian splitting experiment and linear cutting method. We establish fracture deformation analysis method based on CT scan gray image. Through pressurization and depressurization test, the closure law of fractures under different filling conditions and fracture extension length was studied. The research results show that as the confining pressure increases, the fracture width and permeability gradually decrease. The stronger the ductility of the filler is, the more obvious the fracture closure is under pressure, and the greater the permeability reduction is. For the same quartz filled fractures, fracture closure laws are different under different filling methods. For fracture support effect, the single layer fine sand > thick layer fine sand > medium-fine mixture sand. In general, the greater the fracture extension length, the higher the permeability, but the increase of permeability is different. The findings of this study can help for a better understanding of reasons for large differences in single well productivity and contribute to rational productivity optimization of fault-controlled reservoirs.