Experimental Investigation on Permeability Evolution of Dolomite Caprock under Triaxial Compression

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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Experimental Study on Triaxial Unloading Failure of Deep Composite Coal-Rock

Advances in Civil Engineering ◽

10.1155/2021/6687051 ◽

2021 ◽

Vol 2021 ◽

pp. 1-14

Author(s):

Xin Li ◽

Hao Li ◽

Zhen Yang ◽

Zhongxue Sun ◽

Jiayu Zhuang ◽

...

Keyword(s):

Compressive Strength ◽

Failure Criterion ◽

Confining Pressure ◽

Exponential Relationship ◽

Partial Fracture ◽

Triaxial Compressive Strength ◽

Confining Pressures ◽

Unloading Rate ◽

Coal Rock ◽

And Control

With the deep mining of coal, the phenomenon of high ground stress is more likely to cause dynamic disaster. In view of the above problems, this paper takes the unloading process of coal mining as the background to study the effects of mining rates under different conditions on the mechanical properties and triaxial failure criterion of composite coal-rock, so as to provide a theoretical basis for the prevention and control of dynamic disasters in coal mines. The composite coal-rock models with a composite ratio of 1 : 1 : 1 were tested under different unloading rates or confining pressures. The results show that the triaxial unloading process of coal-rock can be divided into five stages: compaction, single elasticity, elastic-plastic unloading, partial fracture, and complete fracture. In this paper, the failure criterion of composite coal-rock triaxial unloading is derived. The unloading rate has an exponential relationship with the triaxial compressive strength, and the relationship between initial confining pressure and compressive strength is linear. The triaxial compressive strength is determined by both. The peak strains ε of all samples under different unloading conditions were around 0.01. And initial confining pressure had an influence on the strain variation trend during the unloading of composite coal-rock. The higher the initial confining pressure, the greater the elastic modulus. In addition, an increase of initial confining pressure led to the increase of the total energy converted into dissipated part in the process of fracture and caused the obvious increase of the rebound characteristics of the curve. However, the unloading rate had no influence on the strain trend.

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Triaxial Testing of Freshwater Ice at Low Confining Pressures

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.2919929 ◽

1991 ◽

Vol 113 (3) ◽

pp. 260-265 ◽

Cited By ~ 3

Author(s):

J. P. Nadreau ◽

A. M. Nawwar ◽

Y. S. Wang

Keyword(s):

Compressive Strength ◽

Strain Rate ◽

Confining Pressure ◽

Peak Temperature ◽

Triaxial Testing ◽

Brittle Transition ◽

Freshwater Ice ◽

Triaxial Compressive Strength ◽

Confining Pressures ◽

Ductile To Brittle Transition

Tests have been conducted on freshwater columnar ice samples to determine the uniaxial and triaxial compressive strength of the ice. Four parameters were varied. The confining pressure was increased up to 2.85 MPa (400 psi) in steps of 0.7 MPa (100 psi). The strain rate was varied in order to obtain the ductile to brittle transition peak. Temperature was kept mainly at −2°, with two series at −10°C and −20°C, and samples were machined with axes parallel, perpendicular or at a 45-deg angle to the direction of ice growth. The results are presented within their original context, but analyzed with reference to recent studies conducted on the multiaxial behavior of ice.

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Comparative Analyses Concerning Triaxial Compressive Yield Criteria of Coal with the Presence of Pore Water

Geofluids ◽

10.1155/2020/4670812 ◽

2020 ◽

Vol 2020 ◽

pp. 1-15 ◽

Cited By ~ 3

Author(s):

Rulin Liu ◽

Yanbin Yu ◽

Weimin Cheng ◽

Qingfeng Xu ◽

Haotian Yang ◽

...

Keyword(s):

Compressive Strength ◽

Uniaxial Compressive Strength ◽

Pore Water ◽

Yield Criterion ◽

Triaxial Compression ◽

Strength Criterion ◽

Confining Pressure ◽

Quadratic Polynomial ◽

Yield Criteria ◽

Triaxial Compressive Strength

The least absolute deviation is used as a metric to analyze the applicability of five yield criteria, to describe the yield characteristics of coal based on triaxial compressive strength tests on natural, water-saturated, and seepage coal samples with the presence of pore water. The results show that the strength of coal exhibits nonlinear characteristics with the increase of confining pressure, which the linear Coulomb criterion fails to authentically describe. Although the parabolic Mohr criterion can describe the nonlinearity feature more decently than the linear yield criterion, the fitting error is significant, and the uniaxial compressive strength of coal is overestimated. The Hoek-Brown criterion, quadratic polynomial criterion, and exponential criterion yield decent fitting quality for the coal rock. In particular, the exponential strength criterion can accurately reflect the actual uniaxial compressive strength of the rock. However, the differential principle yield stress for an infinite confining pressure calculated from the exponential strength criterion is lower than the measured value. Furthermore, by employing effective stress principle to analyze the yield criteria for the saturated and seepage coal samples, one can find that the quadratic polynomial criterion and the exponential criterion can also reflect the changes of yield characteristics during the fluid-solid coupling triaxial compression test.

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Strength of Oil Well Cements at Downhole Pressure-Temperature Conditions

Society of Petroleum Engineers Journal ◽

10.2118/1300-pa ◽

1965 ◽

Vol 5 (04) ◽

pp. 341-347 ◽

Cited By ~ 3

Author(s):

John Handin

Keyword(s):

Pore Pressure ◽

Triaxial Compression ◽

Test Chamber ◽

Confining Pressure ◽

Effect Of Temperature ◽

Oil Well ◽

Effective Pressure ◽

Confining Pressures ◽

The Difference ◽

Cement Strength

Abstract Triaxial compression tests with independently applied external confining pressures and internal pore pressures show that the ultimate compressive strengths of representative oil well cements are nearly linear functions of effective pressure the difference between external and internal pressures on the jacketed cylindrical specimens (to 15,000 psi). The strengths are little affected by the test temperature to 350F (not to be confused with the curing temperature). At an effective pressure of 15,000 psi, strengths are in the range of 30,000 to 50,000 psi, comparable to those of sedimentary rocks under similar conditions. The cements become very ductile even under low effective pressures; permanent shortenings of 30 per cent or more are attainable without rupture. Introduction Since the pioneering work of Richart, Brandtzaeg and Brown on the failure of cement under combined compressive stresses, it has been recognized that ultimate compressive strength is greatly enhanced by the application of confining pressure. More recently, McHenry showed that the strength of concrete was a linear function of the effective pressure (the difference between the external confining pressure on a jacketed specimen and the internal fluid pore pressure) at least for a range of 0 to 1,500 psi. The effect of temperature had not been investigated, and no previous systematic triaxial compression testing of materials used for oilwell cementing seems to have been done. The present work was suggested by the late J. M. Bugbee who stated that "consideration of the common application of high-pressure hydraulic fracturing to the initial completion or recompletion of wells, and the large pressure drawdowns in some producing wells, particularly those in abnormally high-pressure gas-condensate reservoirs, raises the question of what is a suitable cement strength for various completions. The intuitive belief exists that cement strength need be no greater than formation strength. Tests should, however, be conducted at downhole conditions."The ultimate compressive strengths of rocks penetrated by the borehole must rise several fold with increasing depth. This marked enhancement of strength is due to the influence of the effective pressure, the total weight per unit area of the overburden less the hydrostatic pore pressure. (The effect of temperature due to the geothermal gradients is relatively small for depths to 30,000 ft.) A significant comparison of the strengths of rocks and cements at downhole conditions requires knowledge of the confined compressive strengths of cements as well. EXPERIMENTAL PROCEDURES The theory and technique of triaxial compression testing are fully discussed in earlier reports. Briefly, cylindrical specimens 1-in. long and 0.5-in. in diameter are jacketed in thin copper tubes of negligible strength, placed in the test chamber and subjected to an external confining pressure of kerosene and loaded axially by the piston at a strain rate of 1 per cent per minute. Pore pressures of water (or kerosene) are applied independently through the hollow piston and are maintained constant during the shortening of the specimen. Tests at sensibly 0 pore pressure are arranged so that any free water in the cement can escape to the atmosphere. (If egress of water were denied, pore pressure would rapidly attain the value of the external confining pressure because of reduction of pore space.) The test chamber can be heated for high-temperature experiments. Unless other-wise noted, the cement samples were air dried for about a week. Recorded during a test are pore and confining pressures, shortening and axial differential force (total force less the product of the confining pressure and the area of the piston). SPEJ P. 341ˆ

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

Geofluids ◽

10.1155/2019/1796380 ◽

2019 ◽

Vol 2019 ◽

pp. 1-14

Author(s):

Lu Shi ◽

Zhijiao Zeng ◽

Zhiming Fang ◽

Xiaochun Li

Keyword(s):

Turning Point ◽

Triaxial Compression ◽

Volumetric Strain ◽

Ductile Failure ◽

Confining Pressure ◽

Small Strain ◽

Permeability Evolution ◽

The Maximum Principle ◽

Confining Pressures ◽

Onset Of Dilatancy

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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Study on the variation of physical and mechanical characteristics under freeze-thaw condition

E3S Web of Conferences ◽

10.1051/e3sconf/202016503021 ◽

2020 ◽

Vol 165 ◽

pp. 03021

Author(s):

Tian Yanzhe

Keyword(s):

Compressive Strength ◽

Elastic Modulus ◽

Axial Strain ◽

Triaxial Compression ◽

Physical And Mechanical Properties ◽

Peak Stress ◽

Friction Angle ◽

Confining Pressure ◽

Freeze Thaw ◽

Triaxial Compressive Strength

Subjected to freeze-thaw cycles, the deformation of physical and mechanical properties is the main cause of engineering disasters. Based on the analysis of the results of triaxial compression test after different freeze-thaw cycles, conclusions are drawn that: under the certain freeze-thaw cycles conditions, with the increase of confining pressure, the triaxial compressive strength, elastic modulus and the axial strain increase gradually, indicating that the failure of rock changes from brittle failure to plastic failure; in the case of same confining pressure, with the increase of the number of freeze-thaw cycles, the triaxial compressive strength,elastic modulus of rock decreases and the axial strain corresponding to peak stress gradually increase. With the increase of the number of freeze-thaw cycles, the cohesion of grit is in the form of exponentially decays to reduce,the internal friction angle changes very little.

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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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Experimental Investigation of Water-Inrush Risk Based on Permeability Evolution in Coal Mine and Backfill Prevention Discussion

Geofluids ◽

10.1155/2019/3920414 ◽

2019 ◽

Vol 2019 ◽

pp. 1-9 ◽

Cited By ~ 5

Author(s):

Meng Li ◽

Jixiong Zhang ◽

Weiqing Zhang ◽

Ailing Li ◽

Wei Yin

Keyword(s):

Experimental Investigation ◽

Coal Mine ◽

Strain Softening ◽

Water Inrush ◽

Rock Fractures ◽

Permeability Evolution ◽

Testing Laboratories ◽

Fracture Development ◽

Confining Pressures ◽

Maximum Permeability

Induced by coal mining, the fractures constantly occur in geologic strata until failure occurs, which provide channels for water flow. Therefore, it is essential to investigate the permeability evolution of rocks under load. Borehole sampling was conducted in a bedrock layer beneath an aquifer, and the permeability evolution of sandstone specimens under different confining pressures was tested in rock mechanics testing laboratories. The results indicated that the permeability gradually decreases with the increasing confining pressures, while the peak strength increases with the increase of confining pressures. The minimum and maximum permeabilities occurred in the sandstone specimens that were subjected to elastic deformation and strain-softening stages, respectively. The failure, and maximum permeability, of these sandstone specimens did not occur simultaneously. To prevent the flow channel being formed due to the development and failure of rock fractures, a method of backfill gob was proposed and also the influence of backfill on fracture development was discussed.

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Physical and Mechanical Properties of a Bulk Lightweight Concrete with Expanded Polystyrene (EPS) Beads and Soft Marine Clay

Materials ◽

10.3390/ma12101662 ◽

2019 ◽

Vol 12 (10) ◽

pp. 1662 ◽

Cited By ~ 4

Author(s):

Jianguo Wang ◽

Bowen Hu ◽

Jia Hwei Soon

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Cement Content ◽

Mass Density ◽

Physical And Mechanical Properties ◽

Confining Pressure ◽

Expanded Polystyrene ◽

Triaxial Tests ◽

Filling Material ◽

Confining Pressures

The variation of physical and mechanical properties of the lightweight bulk filling material with cement and expanded polystyrene (EPS) beads contents under different confining pressures is important to construction and geotechnical applications. In this study, a lightweight bulk filling material was firstly fabricated with Singapore marine clay, ordinary Portland cement and EPS. Then, the influences of EPS beads content, cement content, curing time and confining pressure on the mass density, stress–strain behavior and compressive strength of this lightweight bulk filling material were investigated by unconsolidated and undrained (UU) triaxial tests. In these tests, the mass ratios of EPS beads to dry clay (E/S) were 0%, 0.5%, 1%, 2%, and 4% and the mass ratios of cement to dry clay (C/S) were 10% and 15%. Thirdly, a series of UU triaxial tests were performed at a confining pressure of 0 kPa, 50 kPa, 100 kPa, and 150 kPa after three curing days, seven curing days, and 28 curing days. The results show that the mass density of this lightweight bulk filling material was mainly controlled by the E/S ratio. Its mass density decreased by 55.6% for the C/S ratio 10% and 54.9% for the C/S ratio 15% when the E/S ratio increased from 0% to 4% after three curing days. Shear failure more easily occurred in the specimens with higher cement content and lower confining pressure. The relationships between compressive strength and mass density or failure strain could be quantified by the power function. Increasing cement content and reducing EPS beads content will increase mass density and compressive strength of this lightweight bulk filling material. The compressive strength with curing time can be expressed by a logarithmic function with fitting correlation coefficient ranging from 0.83 to 0.97 for five confining pressures. These empirical formulae will be useful for the estimation of physical and mechanical properties of lightweight concretes in engineering application.

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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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