Investigation of the Effect of Confining Pressure on the Mechanics-Permeability Behavior of Mudstone under Triaxial Compression

Injecting CO2 into a reservoir disturbs the geostress field, which leads to variations in the permeability of caprock and affects its sealing performance. In this paper, the evolution characteristics of the permeability of Yingcheng mudstone were experimentally studied during deviatoric compression under different confining pressures. As the confining pressure increased, the strength of the mudstone increased bilinearly, the angle between the fault and the maximum principle stress increased, and the fault became flatter. During compression, the permeability of mudstone first decreased and then increased and the turning point of the permeability was between the onset of dilatancy and the turning point of volumetric strain; when the fault formed, the permeability increased sharply and the fault-induced increment was reduced exponentially with increasing confining pressure. In addition, the mudstone transformed to the ductile failure mode when the effective confining pressure was greater than 35 MPa, which means that the permeability did not jump within a small strain. Finally, a practical strain-based model of permeability evolution that separately considers compaction and dilatancy was proposed, and the predicted permeability values were in good agreement with the experimental results. This study revealed the effect of confining pressure on permeability evolution during compression and can help evaluate the sealing ability of mudstone caprock.

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Mechanical behaviour of powders using a medium pressure flexible boundary cubical triaxial tester

Proceedings of the Institution of Mechanical Engineers Part E Journal of Process Mechanical Engineering ◽

10.1243/095440803322328881 ◽

2003 ◽

Vol 217 (3) ◽

pp. 233-241 ◽

Cited By ~ 11

Author(s):

F Li ◽

V M Puri

Keyword(s):

Shear Modulus ◽

Mechanical Behaviour ◽

Triaxial Compression ◽

Three Dimensional ◽

Volumetric Strain ◽

Confining Pressure ◽

Alumina Powder ◽

Medium Pressure ◽

Mean Pressure ◽

Confining Pressures

A medium pressure (<21 MPa) flexible boundary cubical triaxial tester was designed to measure the true three-dimensional response of powders. In this study, compression behaviour and strength of a microcrystalline cellulose powder (Avicel® PH102), a spray-dried alumina powder (A16SG), and a fluid-bed-granulated silicon nitride based powder (KY3500) were measured. To characterize the mechanical behaviour, three types of triaxial stress paths, that is, the hydrostatic triaxial compression (HTC), the conventional triaxial compression (CTC), and the constant mean pressure triaxial compression (CMPTC) tests were performed. The HTC test measured the volumetric response of the test powders under isostatic pressure from 0 to 13.79MPa, during which the three powders underwent a maximum volumetric strain of 40.8 per cent for Avicel® PH102, 30.5 per cent for A16SG, and 33.0 per cent for KY3500. The bulk modulus values increased 6.4-fold from 57 to 367MPa for Avicel® PH102, 3.7-fold from 174 to 637 MPa for A16SG, and 8.1-fold from 74 to 597MPa for KY3500, when the isotropic stress increased from 0.69 to 13.79 MPa. The CTC and CMPTC tests measured the shear response of the three powders. From 0.035 to 3.45MPa confining pressure, the shear modulus increased 28.7-fold from 1.6 to 45.9MPa for Avicel® PH102, 35-fold from 1.7 to 60.5MPa for A16SG, and 28.5-fold from 1.5 to 42.8MPa for KY3500. In addition, the failure stresses of the three powders increased from 0.129 to 4.41 MPa for Avicel® PH102, 0.082 to 3.62 MPa for A16SG, and 0.090 to 4.66MPa for KY3500, respectively, when consolidation pressure increased from 0.035 to 3.45MPa. In addition, the shear modulus and failure stress values determined from the CTC test at 2.07, 2.76, and 3.45MPa confining pressures are consistently greater than those from the CMPTC test at the same constant mean pressures. This observation demonstrates the influence of stress paths on material properties. The CTT is a useful tool for characterizing the three-dimensional response of powders and powder mixtures.

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Triaxial Compressive Failure Characteristics and Constitutive Model Study of Jurassic-Cretaceous Weakly Cemented Sandstone

Advances in Civil Engineering ◽

10.1155/2020/8812575 ◽

2020 ◽

Vol 2020 ◽

pp. 1-12

Author(s):

Jinlong Cai ◽

Wei Zou

Keyword(s):

Constitutive Model ◽

Residual Strength ◽

Triaxial Compression ◽

Volumetric Strain ◽

Ductile Failure ◽

Mathematical Expression ◽

Confining Pressure ◽

Mining Area ◽

Peak Strength ◽

Correction Coefficient

A conventional triaxial compression test of Jurassic-Cretaceous typical weakly consolidated sandstone from a mining area in Ordos, China, was conducted using an MTS816 tester. Results showed that, before the peak, the rock had a distinct yield stage. When the specimen reached its peak strength, the strength decreased rapidly and showed an obvious brittle failure. When the confining pressure was increased to 15 MPa, the decrease of strength was slow and the rock tended toward ductile failure. With the increase of confining pressure, the cyclic strain initially increased slightly, whereas the volumetric strain increased greatly and the rock sample was in a compression state. When the load reached a critical value, the curve was reversely bent, resulting in volume expansion, whereas the peak strength, residual strength, and elastic modulus increased with confining pressure, and Poisson’s ratio decreased with the confining pressure. In the model based on macroscopic failure rock, the expression of the relationship between fracture angle and confining pressure provided a solid theoretical basis for the direction and failure mode of the macroscopic crack. Based on the rock strength theory and Weibull random distribution assumption of rock element strength, the damage variable correction coefficient was introduced when the residual strength was considered. Then, the mathematical expression of the 3D damage statistical constitutive model was established. Finally, the theoretical curve of the established constitutive model was compared with the triaxial test curve, which showed a high degree of coincidence.

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Experimental Research into the Evolution of Permeability of Sandstone under Triaxial Compression

Energies ◽

10.3390/en13195065 ◽

2020 ◽

Vol 13 (19) ◽

pp. 5065

Author(s):

Liming Zhang ◽

Shengqun Jiang ◽

Jin Yu

Keyword(s):

Axial Strain ◽

Triaxial Compression ◽

Testing Machine ◽

Volumetric Strain ◽

Confining Pressure ◽

Rate Of Change ◽

Peak Strength ◽

Sudden Increase ◽

Seepage Pressure ◽

Confining Pressures

Failure tests on sandstone specimens were conducted under different confining pressures and seepage pressures by using an MTS triaxial rock testing machine to elucidate the corresponding correlations of permeability and characteristic stress with confining pressure and pore pressure during deformation. The results indicate that permeability first decreases and presents two trends, i.e., a V-shaped increase and an S-shaped trend during the non-linear deformation stage. The greater the seepage pressure, the greater the initial permeability and the more obvious the V-shaped trend in the permeability. As the confining pressure was increased, the trend in the permeability gradually changed from V- to S-shaped. Compared with the case at a high confining pressure, the decrease of permeability occurred more quickly, the rate of change becomes greater, and the sudden increase observed in the permeability happened earlier under lower confining pressures. Within the range tested, confining pressure exerted a greater effect on the permeability than the seepage pressure. In comparison with the axial strain, volumetric strain better reflected changes in permeability during compaction and dilation of sandstone. The ratio of crack initiation stress to peak strength ranged from 0.37 to 0.50, while the ratio of dilation stress to peak strength changed from 0.58 to 0.72. Permeabilities calculated based on Darcy and non-Darcy flow changed within the same interval, while the change in permeability was different.

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Influence of Unloading Conditions of Confining Pressure on the Compressive Strength and Permeability of Deep Mudstone

Advances in Civil Engineering ◽

10.1155/2021/6611377 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Tianyu Xin ◽

Yashengnan Sun ◽

Junguang Wang ◽

Weiji Sun

Keyword(s):

Compressive Strength ◽

Brittle Failure ◽

Axial Stress ◽

Triaxial Compression ◽

Volumetric Strain ◽

Ductile Failure ◽

Confining Pressure ◽

Initial Stage ◽

Strain Change ◽

Deep Rock

To investigate the compressive strength and permeability of deep mudstone under stress disturbance, a triaxial rheometer is used to conduct seepage experiments on mudstone specimens with different buried depths under triaxial compression and unloading conditions. The experimental results show that the compressive strength of mudstone specimen with a depth of 1000 m is much lower than that of specimen with a depth of 200 m, and the compressive strength of mudstone increases with the increase in confining pressure. Under constant axial pressure and unloading of the confining pressure, the mudstone with a depth of 200 m exhibits brittle failure, and the strain fluctuates in a pointwise manner with the increase in axial stress. In this case, the mudstone with a depth of 1000 m exhibits a transition from brittle failure to ductile failure, and the strain fluctuates linearly with the axial stress. Further, when the volumetric strain change reaches 0.01, it shows an oblique “Z” fluctuation. During the initial stage of unloading of confining pressure, the permeabilities of both the mudstone specimens (with depths of 200 and 1000 m) decrease gradually. As the confining pressure is unloaded, the permeability of mudstone with a depth of 1000 m increases. Until the specimen is completely destroyed, the permeability of mudstone increases rapidly. Overall, this study can serve as a useful reference for analyzing the engineering disasters associated with deep rock mass, tunnel ventilation, and gas storage.

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Investigating the Permeability of Marble under Moderate Pressure and Temperature

Geofluids ◽

10.1155/2017/4126908 ◽

2017 ◽

Vol 2017 ◽

pp. 1-8 ◽

Cited By ~ 2

Author(s):

Jianping Yang ◽

Weizhong Chen ◽

Diansen Yang ◽

Hongming Tian

Keyword(s):

Volumetric Strain ◽

Strain Curve ◽

Confining Pressure ◽

Crystalline Rock ◽

Mechanical Tests ◽

Moderate Pressure ◽

Test Results ◽

Permeability Evolution ◽

Confining Pressures ◽

Linkage Model

The permeability of intact marble samples collected from the depth of 1.6 km in southwestern China is investigated under moderate confining pressures and temperatures. No microcracks initiate or propagate during the tests, and the variation of permeability is due to the change of aperture of microcracks. Test results show a considerable decrease of permeability along with confining pressure increase from 10 to 30 MPa and temperature increase from 15 to 40°C. The thermal effect on the permeability is notable in comparison with the influence of the stress. A simple permeability evolution law is developed to correlate the permeability and the porosity in the compressive regime based on the microphysical geometric linkage model. Using this law, the permeability in the compressive regime for crystalline rock can be predicted from the volumetric strain curve of mechanical tests.

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Experimental Investigation on Permeability Evolution of Dolomite Caprock under Triaxial Compression

Energies ◽

10.3390/en13246535 ◽

2020 ◽

Vol 13 (24) ◽

pp. 6535

Author(s):

Deng Xu ◽

Jianfeng Liu ◽

Zhide Wu ◽

Lu Wang ◽

Hejuan Liu ◽

...

Keyword(s):

Compressive Strength ◽

Triaxial Compression ◽

Confining Pressure ◽

Test Machine ◽

Permeability Evolution ◽

Triaxial Compressive Strength ◽

Confining Pressures ◽

Porosity And Permeability ◽

The Difference ◽

Maximum Permeability

In order to study the influence of different confining pressures on the stability and airtightness of dolomite underground gas storage, a permeability test under hydrostatic confining pressure, conventional triaxial compression test and gas–solid coupling test under triaxial compression were carried out on MTS815 test machine. During the tests, an acoustic emission (AE) monitoring system was also employed to estimate the rock damage. The experimental results showed that the relationships between permeability, porosity and hydrostatic confining pressure were exponential function and power function, respectively. Increasing confining pressure reduced the porosity and permeability of dolomite, and increased its triaxial compressive strength, but the addition of nitrogen reduced the compressive strength of dolomite by 10~30%, the higher the confining pressure, the smaller the difference. Compared with the maximum permeability under 15 MPa, confining pressure in the gas–solid coupling experiment, the maximum permeability under confining pressure of 30, 45, and 60 MPa is reduced by 42.0%, 84.4%, and 97.9%, respectively. In addition, the AE activity of dolomite decreases significantly with the increase in confining pressure, which also delayed the arrival of the AE active period.

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Dilatancy behaviour and permeability evolution of sandstone subjected to initial confining pressures and unloading rates

Royal Society Open Science ◽

10.1098/rsos.201792 ◽

2021 ◽

Vol 8 (1) ◽

pp. 201792

Author(s):

Honggang Zhao ◽

Chao Liu ◽

Gun Huang

Keyword(s):

Mechanical Response ◽

Axial Stress ◽

Deformation Behaviour ◽

Crack Density ◽

Volumetric Strain ◽

Confining Pressure ◽

Permeability Evolution ◽

Confining Pressures ◽

Sandstone Permeability ◽

Shear Dilatancy

Mechanical response, deformation behaviour and permeability evolution of surrounding rock under unloading conditions are of significant importance in rock engineering activities. In this research, triaxial experiments of sandstone subjected to different initial confining pressures and unloading rates under fixed axial stress were conducted. The results showed that sandstones experienced shear dilatancy before failure. However, the dilatancy factor did not decrease with increasing confining pressure, i.e. the dilatancy behaviour was not suppressed, which contradicted the phenomenon under increasing axial stress. The crack density also increased with increasing initial confining pressure. Furthermore, the normalized permeability was positively correlated with unloading rates. The sandstone permeability was closely related to the shear dilatancy behaviour. In the accelerated dilatancy stage, the relationship between normalized permeability and volumetric strain was linear at low unloading rates and nonlinear at high unloading rates. The linear/nonlinear relationship between them can directly affect the temporality of respective mutation, so as to guide the prevention of geological disasters at different excavations rates.

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Experimental investigation of the effect of compliant pores on reservoir rocks under hydrostatic and triaxial compression stress states

Canadian Geotechnical Journal ◽

10.1139/cgj-2018-0133 ◽

2019 ◽

Vol 56 (7) ◽

pp. 983-991

Author(s):

Hua Yu ◽

Kam Ng ◽

Dario Grana ◽

John Kaszuba ◽

Vladimir Alvarado ◽

...

Keyword(s):

Pore Pressure ◽

Triaxial Compression ◽

Matrix Material ◽

Volumetric Strain ◽

Confining Pressure ◽

Differential Pressure ◽

Sandstone Sample ◽

Stress States ◽

Rock Springs ◽

Stage 1

The presence of compliant pores in rocks is important for understanding the stress–strain behaviors under different stress conditions. This paper describes findings on the effect of compliant pores on the mechanical behavior of a reservoir sandstone under hydrostatic and triaxial compression. Laboratory experiments were conducted at reservoir temperature on Weber Sandstone samples from the Rock Springs Uplift, Wyoming. Each experiment was conducted at three sequential stages: (stage 1) increase in the confining pressure while maintaining the pore pressure, (stage 2) increase in the pore pressure while maintaining the confining pressure, and (stage 3) application of the deviatoric load to failure. The nonlinear pore pressure – volumetric strain relationship governed by compliant pores under low confining pressure changes to a linear behavior governed by stiff pores under higher confining pressure. The estimated compressibilities of the matrix material in sandstone samples are close to the typical compressibility of quartz. Because of the change in pore structures during stage 1 and stage 2 loadings, the estimated bulk compressibilities of the sandstone sample under the lowest confining pressure decrease with increasing differential pressure. The increase in crack initiation stress is limited with increasing differential pressure because of similar total crack length governed by initial compliant porosity in sandstone samples.

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Experimental Research on Deformation Characteristics and Energy Change of Rock under Different Unloading Rates of Confining Pressures

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.243-249.2885 ◽

2011 ◽

Vol 243-249 ◽

pp. 2885-2888

Author(s):

Xian Min Han ◽

Shou Ding Li

Keyword(s):

Rock Mass ◽

Energy Release ◽

Rock Burst ◽

Experimental Research ◽

Volumetric Strain ◽

Confining Pressure ◽

Deformation Characteristics ◽

Confining Pressures ◽

Unloading Rate ◽

Unloading Confining Pressure

Experiments of unloading confining pressure of rock were conducted to reveal deformation characteristics of rock mass under different excavation intension in thigh geostress condition. It were concluded from tests that volumetric strain of rock is inverse proportional to unloading rate. The smaller the unloading rate, the bigger the ductility of rock. Energy release are bigger under high unloading rate than that under low unloading rate. That means that tendency of rock burst turn smaller when unloading rates decrease.

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The Effect of Confining Pressure on the Mechanical Properties of Sand–Ice Materials

Journal of Glaciology ◽

10.1017/s0022143000031889 ◽

1973 ◽

Vol 12 (66) ◽

pp. 469-481 ◽

Cited By ~ 42

Author(s):

Bernard D. Alkire ◽

Orlando B. Andersland

Keyword(s):

Axial Strain ◽

Triaxial Compression ◽

Confining Pressure ◽

Silica Sand ◽

Creep Tests ◽

Ice Volume ◽

Coulomb Failure ◽

Confining Pressures ◽

Sand Material ◽

Cylindrical Samples

Cylindrical samples containing 0.59 mm to 0.84 mm diameter silica sand at about 97% and 55% ice saturation (the ratio of ice volume to sand pore volume) were tested at a temperature of −12° C in triaxial compression. Both constant axial strain-rate tests and step-stress creep tests provide information on the influence of confining pressure on the shear strength and creep behavior of the sand–ice material. Changes in the degree of ice saturation help show the influence of the ice matrix versus the sand material on the mechanical behavior. Data are discussed in terms of the Mohr–Coulomb failure law and creep theories. It is shown that the cohesive component of strength depends on response of the ice matrix, whereas the frictional component of strength responds in a manner very similar to unfrozen sand tested at high confining pressures. Experimental data show that creep rates decrease exponentially and creep strength increases with an increase in confining pressure.

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