scholarly journals Investigation on the Influence of Temperature and Confining Pressure on the Hydraulic Conductivity of the Integrated and Fractured Jurassic Conglomerates

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Dingyang Zhang ◽  
Wanghua Sui ◽  
Jiawei Liu
Keyword(s):  
Hydraulic Conductivity ◽  
Shear Failure ◽  
Negative Relationship ◽  
Confining Pressure ◽  
Regression Equations ◽  
Intact Sample ◽  
Triaxial Cell ◽  
Different Temperatures ◽  
Confining Pressures ◽  
Constant Head

This paper presents an experimental investigation on the properties of hydraulic conductivity and permeability of conglomerates under different temperatures and confining pressures with integrated samples and samples with shear failure. Constant head tests were carried out in a temperature-controlled triaxial cell with samples obtained from the Zhuxianzhuang Coal Mine. Five levels of temperatures (10°C, 20°C, 28°C, 35°C, and 50°C) and three levels of confining pressures (3 MPa, 5 MPa, and 7 MPa) were chosen for the tests. The results show that there is a negative relationship between hydraulic conductivity and confining pressure with both original and shear failure samples. An inflection point of 35°C is found in the relationship between the flow rate and temperature. However, with increasing temperature conditions, hydraulic conductivity first increases and then decreases at 50°C with the intact sample, while hydraulic conductivity first decreases from 20°C and then increases with the shear failure sample. Finally, nonlinear regression equations of hydraulic conductivity and temperature were obtained under different confining pressures.

scholarly journals The meso-fracturing mechanism of marble under unloading confining pressure paths and constant axial stress

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Linna Sun ◽  
Liming Zhang ◽  
Yu Cong ◽  
Yaduo Song ◽  
Keqiang He
Keyword(s):  
Shear Failure ◽  
Axial Stress ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Confining Pressures ◽  
Tension Cracks ◽  
Trial And Error Method ◽  
Unloading Confining Pressure ◽  
Fracturing Mechanism

AbstractFailure tests on marble during unloading confining-pressure under constant axial stress and simulations with the particle flow code were performed. The influence mechanism of the unloading rate of the confining pressure, initial unloading stress, and confining pressure on the failure characteristics of, and crack propagation in, marble was studied. By using the trial-and-error method, the conversion relationship between the unloading rates of confining pressures in laboratory tests and numerical simulations was ascertained. Micro-cracks formed in the unloading process of confining pressure are dominated by tension cracks, accompanied by shear cracks. The propagation of shear cracks lags that of tension cracks. As the confining pressure is increased, more cracks occur upon failure of the samples. The proportion of shear cracks increases while that of tension cracks decreases. The failure mode of samples undergoes a transition from shear-dominated failure to conjugated shear failure.

scholarly journals Experimental study on the thermal damage characteristics of cement stone

2020 ◽  
pp. 317-317
Author(s):  
Feng Xu ◽  
Bowen Qian ◽  
Ling Tan ◽  
Jianqiang Xu ◽  
Shengchuan Tang ◽  
...  
Keyword(s):  
Strain Curve ◽  
Horizontal Wells ◽  
Friction Angle ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Cement Stone ◽  
Different Temperatures ◽  
Confining Pressures ◽  
Southwest Region ◽  
Sealing Failure

Aiming at the problem of cement ring sealing failure during deep high-temperature shale gas exploitation, comprehensively considering the influence of the characteristics of multi-cluster fracturing of multiple horizontal wells and formation temperature, the cementing cement the southwest region is taken as the research object. After exposure to different temperatures (95?C and 135?C) and for different times (5, 10 and 20 times), axial and triaxial tests with different confining pressures (0, 5 MPa, 15 MPa and 30 MPa) were carried out. The research shows that: (1) the stress-strain curve of cement stone after heat treatment can be divided into four stages: compaction, elastic, yield and post-peak stage. As the confining pressure increases, the compaction phase disappears, the yield phase increases, and we see the transition from brittle to ideal plasticity after the peak; (2) as the temperature and number of thermal cycles increase, the cohesive force decreases significantly, and the internal friction angle shows a slight increase. The elastic modulus and the peak strength decreased.

scholarly journals Cut-Through Fractured Seepage Properties and Numerical Simulation of Sandstone after Different Temperature Treatments

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Haopeng Jiang ◽  
Annan Jiang
Keyword(s):  
Fracture Surface ◽  
Shear Failure ◽  
Failure Surface ◽  
Confining Pressure ◽  
Theoretical Formula ◽  
Negative Exponential Function ◽  
Damage Degree ◽  
Different Temperatures ◽  
Negative Exponential ◽  
Fractured Sandstone

To explore the seepage characteristics of cut-through fractured rocks after different temperatures, sandstone in the Hunan area was selected as the research object. First, the influence degree of different temperatures on the permeability of fractured sandstone was studied, and the permeability variation of fractured sandstone with net confining pressure was revealed. The test data was nonlinearly fitted to prove that the relationship between permeability and net confining pressure conforms to the characteristics of the negative exponential function. Second, the macroscopic fractured state of sandstone after different temperature treatments was analyzed, and it is concluded that the inclination angle of the fracture surface decreases with the applied thermal temperature, the fracture surface gradually develops into a single shear failure surface, and the damage degree becomes more and more serious. Finally, the theoretical formula for the calculation of fractured seepage was introduced, and the FLAC3D embedded fish language was used to compile the seepage-stress coupling calculation program of the fractured sandstone after different temperature treatments. Numerical calculations were carried out based on samples with different fracture angles of fractured sandstone, and the calculated values were in good agreement with the test results. The research results can provide guiding significance for the research on the influence of high temperature in fire tunnel on the evolution of permeability of surrounding rock fissures.

IMPACT OF WATER AND CO2 ON THE MECHANICAL PROPERTIES OF LOW PERMEABLE ROCKS

2021 ◽  
Vol 7 (2) ◽  
pp. 130-146
Author(s):  
Anatolii A. KISLITSYN ◽  
Nikita V. Lipatov
Keyword(s):  
Mechanical Properties ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Strength Properties ◽  
Pore Fluid ◽  
Co2 Injection ◽  
Core Samples ◽  
Different Temperatures ◽  
Confining Pressures ◽  
Temporary Decrease

This article features experiments on triaxial compression of low-permeable dolomite samples with different confining pressures (2-20 MPa), different pore fluids (dry air, water, CO2), and different temperatures (25-150 °C). The authors have studied the effect of confining pressure, pore fluid and temperature on the strength properties of the studied samples. The results show an increase in the strength with grwoing confining pressure. When the confining pressure increases from 2 to 20 MPa, the compressive strength increases from 86 to 370 MPa. Temperature has a significant effect on rock strength under low confining pressure conditions. With the increasing confining pressure reaching 15 MPa, increasing temperature has little effect on the strength of dolomite samples. Under an effective confining pressure of 5 MPa, the temperature weakening occurs on the dolomite specimens when the temperature exceeds 90 °C. During compression, liquid diffusion occurs in the specimens. Higher water viscosity can cause a temporary decrease in effective confining pressure, which can increase the strength of the rock. More prominent fractures are observed in the samples, and more fluid is injected under CO2 injection conditions, which may be useful for increasing the permeability of the geothermal reservoir. Two groups of experiments have been performed on the samples in this study: the first group of experiments investigated the effect of confining pressure on the fracture stress of core samples, without pore fluid injection; the second group of experiments investigated the effect of water or CO2 and temperature on the mechanical properties of core samples.

scholarly journals Long-term creep behavior of deep-buried marble under different confining pressures

2019 ◽  
Vol 23 (Suppl. 3) ◽  
pp. 653-660
Author(s):  
Ersheng Zha ◽  
Ru Zhang ◽  
Zetian Zhang ◽  
Li Ren ◽  
Wenju Zhang ◽  
...  
Keyword(s):  
Creep Behavior ◽  
Shear Failure ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Creep Failure ◽  
Failure Characteristics ◽  
Underground Caverns ◽  
Confining Pressures ◽  
Term Creep

To explore the long-term creep behavior of deep rock, the long-term tri-axial creep mechanical behavior of the rock under different confining pressures has been carried out. The results show that the instantaneous strain and creep strain of the high confining pressure specimen are significantly higher than that of the low confining pressure specimen under high deviatoric stress. By analyzing the failure characteristics of different confining pressure specimens, it is found that with the increase of the confining pressure, the creep failure characteristics of the marble transforms from tensile failure to shear failure. These research results have certain reference significance for the long-term stability analysis of the deep underground caverns.

Studies on Mode II Rock Crack Propagation on Different Loading Environments

2016 ◽  
Vol 713 ◽  
pp. 305-308
Author(s):  
C. Cheng ◽  
M.X. Li ◽  
Y. Liu ◽  
X. Zhang ◽  
Y.Y. Cheng ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Confining Pressure ◽  
Element Model ◽  
Mode Ii ◽  
Geological Exploration ◽  
Underground Engineering ◽  
Different Temperatures ◽  
Confining Pressures ◽  
New Type ◽  
The Stability

In this paper, a new type of specimen, which can be easily made by rock core through geological exploration, of mode II rock crack has been designed and processed. The crack propagation forces F of the specimen are measured under different temperatures and different confining pressures. The crack extension patterns are observed. The 3D finite element model of the specimen is established. The stresses near crack tip are calculated to get the value of KIIC when the crack initiation. The variation of KIIC of the model II rock crack is obtained under different temperatures and confining pressures. The experiments and numerical results show that temperature and confining pressure have obviously influence on KIIC, the value of KIIC decreases with the temperature increasing, and increases with the confining pressure increasing. The results of the paper can provide an important reference for analyzing the stability of the rock cracks in underground engineering.

scholarly journals Experimental Investigation of Unloading-Induced Red Sandstone Failure: Insight into Spalling Mechanism and Strength-Weakening Effect

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Yong Luo ◽  
Fengqiang Gong ◽  
Dongqiao Liu
Keyword(s):  
Shear Failure ◽  
Hard Rock ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Compression Tests ◽  
Failure Characteristics ◽  
Red Sandstone ◽  
Confining Pressures ◽  
Unloading Rate ◽  
Rock Tunnels

To study the effect of excavation unloading on hard rock failure, a series of true-triaxial compression tests, biaxial compression tests, and true-triaxial unloading compression tests (two different unloading rates) at different confining pressures was conducted on red sandstone cube samples. The strength and failure characteristics and their relationship for red sandstone unloading at different unloading rates and confining pressures were analyzed. Based on the test results, the effects of the unloading rate and confining pressure on the strength and failure characteristics of hard rock were explored, and a reasonable explanation for unloading-induced spalling in hard rock tunnels was presented. The results show the stress-strain curve of highly stressed red sandstone exhibits a stress step during unloading, and the higher the unloading rate, the lower the stress level required for a stress step. The rock strength-weakening effect induced by unloading was confirmed. The mechanical properties of red sandstone become more unstable and complicated after unloading. After the red sandstone is unloaded to a two-dimensional stress state, with increasing confining pressure, the strength increases first and then decreases; the failure mode changes from a low-confining pressure tensile-shear failure to a high-confining pressure tensile failure; and the geometries of the slabs change from large thick plates and wedges to medium- and small-sized thin plates. At equal confining pressures, the higher the unloading rate, the lower the strength (i.e., the strength-weakening effect is more pronounced), the thinner the slab, and the lower the confining pressure required for the failure mode to change from tensile-shear failure to tensile failure. The unloading rate and confining pressure affect the strength and failure characteristics by affecting the crack initiation type and propagation direction in hard rock. For deep hard rock tunnels with high unloading rate and axial stress, neglecting the effects of unloading rate and axial stress will lead to a dangerous support design. For deep hard rock ore, if the maximal horizontal principal stress exceeds the critical confining pressure, the mining surface should be perpendicular to the direction of the minimal horizontal principal stress. The results of this study are of great engineering significance for guiding deep hard rock tunnel construction and mining.

Permeability of mine tailings measured in triaxial cell

2019 ◽  
Vol 56 (4) ◽  
pp. 587-599
Author(s):  
Hernán Patiño ◽  
Eliana Martínez ◽  
Jesús González ◽  
Antonio Soriano
Keyword(s):  
Mine Tailings ◽  
Confining Pressure ◽  
Degree Of Saturation ◽  
Consolidation Pressure ◽  
Coefficient Of Permeability ◽  
Triaxial Cell ◽  
Empirical Function ◽  
Hydraulic Gradients ◽  
The Mean ◽  
Constant Head

The execution of permeability tests using a triaxial cell makes it possible to eliminate the uncertainties that characterize tests performed using conventional equipment. This paper contains the results of 48 tests carried out on three materials recovered from tailings of Riotinto mines (Spain). The equipment involved a modified triaxial system to facilitate the execution of permeability tests under constant head. The tests were performed on samples consolidated to 50, 100, 200, and 300 kPa for four different hydraulic gradients established by applying a backpressure difference (ΔBp). The magnitude of the backpressure difference was applied as a percentage of the initial effective consolidation pressure, expressed as ΔBp/[Formula: see text]; namely, values of 10%, 15%, 20%, and 25%, which resulted in hydraulic gradients between 5 and 80. The backpressure (Bp) was constant (400 kPa) in all cases, allowing a degree of saturation close to 100% to be achieved. This was verified by calculating Skempton’s B parameter, which was very close to unity in all cases. The results indicate that it is feasible to define an empirical function including the coefficient of permeability (k) and the effective consolidation pressure ([Formula: see text]), the mean effective confining pressure ([Formula: see text]), and the backpressure differential (ΔBp).

scholarly journals Experimental Study on the Permeability of Quartz Sandstone under Coupled Thermo-Hydromechanical Loading

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 5) ◽  
Author(s):  
Yu Zhang ◽  
Tingting Yu ◽  
Jianwei Li ◽  
Yun Jia ◽  
Dayong Li
Keyword(s):  
Experimental Study ◽  
Structural Stability ◽  
Fluid Pressure ◽  
Confining Pressure ◽  
Experimental Results ◽  
Petroleum Engineering ◽  
Different Temperatures ◽  
Confining Pressures ◽  
Fully Coupled

Abstract This paper focuses on the influence of coupled thermo-hydromechanical processes on the permeability of quartz sandstone. The permeability has been studied under five different confining pressures, three different temperatures, and three fluid pressures. The experimental results exhibit that the permeability of quartz sandstone decreases with the increase of confining pressure while it increases with temperature and fluid pressure. The identification of permeability under fully coupled thermo-hydromechanical conditions is also studied via the realization of four coupled tests. One observes that the temperature plays a more important role on the permeability with respect to the fluid pressure. Moreover, the influence of fluid pressure on the permeability of studied sandstone has been amplified by the temperature. The obtained experimental results allow us to get a good understanding of the permeability of quartz sandstone in petroleum engineering and can help us to guarantee the long-term structural stability.

Investigation on Creep Characteristics of Rock-Like with Precast Internal Fissures under Different Temperatures and Confining Pressures

2021 ◽  
Vol 1032 ◽  
pp. 120-125
Author(s):  
Peng Du ◽  
Yong Yan Wang
Keyword(s):  
Failure Time ◽  
High Stress ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Effect Of Temperature ◽  
Creep Process ◽  
Creep Stage ◽  
Accelerated Creep ◽  
Different Temperatures ◽  
Confining Pressures

In order to study the effect of temperature-confining pressure coupling on the creep behavior of rock-like specimen with precast internal fissures, the creep tests under different temperatures and confining pressures are carried out. The test results show that the rock presents primary creep stage and steady creep stage at low stress levels. Under the condition of high stress, the creep process of rock shows an obvious accelerated creep stage. The curve of accelerated creep stage of rock gradually smoothing with the increase of confining pressure, and the corresponding creep failure time gradually increases. The failure under low confining pressure is mainly tensile failure. The high confining pressure is the shear failure, or even the mixture of shear and plastic failure.

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