scholarly journals Experimental Study on the Permeability Evolution and Gas Flow Law of Post-Strength Soft Coal

2020 ◽  
Vol 10 (3) ◽  
pp. 1039
Author(s):  
Chao Hou ◽  
Jianhong Ma ◽  
Xiaoguang Jin ◽  
Du Ni
Keyword(s):  
Experimental Study ◽  
Gas Flow ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Permeability Evolution ◽  
Axial Pressure ◽  
Soft Coal ◽  
Secondary Damage ◽  
Flow Law ◽  
Gas Disasters

Permeability is an essential indicator for predicting gas drainage yield and preventing mine gas disasters, which is significantly influenced by the stress paths and the integrity of coal. Conventional research on permeability mainly focused on the permeability evolution of initial undamaged or fractured (prefabricated fractures) coal under various stress paths; little attention has been paid to post-strength coal (stress-induced damage), especially for soft coal. To determine the permeability evolution and gas flow law of post-strength soft coal samples under various stress paths, we used the experimental method combined with the numerical method in this study. The results showed that when the confining pressure and axial pressure of post-strength soft coal samples were unloaded, the permeability increased by 1.25–1.32 times; when the coal samples were loaded into the secondary damage, the permeability first decreased and then increased. The simulation part in this study found that the development of the fracture of coal samples under triaxial compression was divided into four stages. Gas flow law of post-strength soft coal was significantly influenced by fracture locations, and the gas pressure and gas flow field near the fracture were disturbed.

scholarly journals Gas Permeability Change with Deformation and Cracking of a Sandstone under Triaxial Compression

2021 ◽  
Author(s):  
Yuan-Jian LIN ◽  
Jiang-Feng LIU ◽  
Tao CHEN ◽  
Shi-Jia MA ◽  
Pei-Lin WANG ◽  
...  
Keyword(s):  
Gas Permeability ◽  
Axial Stress ◽  
Triaxial Compression ◽  
Gas Injection ◽  
Injection Pressure ◽  
Confining Pressure ◽  
Loading Path ◽  
Permeability Evolution ◽  
Axial Pressure ◽  
Triaxial Cell

Abstract In this paper, a THMC multi-field coupling triaxial cell was used to systematically study the evolution of gas permeability and the deformation characteristics of sandstone. The effects of confining pressure, axial pressure and air pressure on gas permeability characteristics were fully considered in the test. The gas permeability of sandstone decreases with increasing confining pressure. When the confining pressure is low, the variation of gas permeability is greater than the variation of gas permeability at high confining pressure. The gas injection pressure has a significant effect on the gas permeability evolution of sandstone. As the gas injection pressure increases, the gas permeability of sandstone tends to decrease. At the same confining pressure, the gas permeability of the sample during the unloading path is less than the gas permeability of the sample in the loading path. When axial pressure is applied, the axial stress has a significant influence on the permeability evolution of sandstone. When the axial pressure is less than 30 MPa, the gas permeability of the sandstone increases as the axial pressure increases. At axial pressures greater than 30 MPa, the permeability decreases as the axial pressure increases. Finally, the micro-pore/fracture structure of the sample after the gas permeability test was observed using 3D X-ray CT imaging.

scholarly journals Gas Permeability Change With Deformation and Cracking of a Sandstone Under Triaxial Compressiongas Permeability Change With Deformation and Cracking of a Sandstone Under Triaxial Compression

2022 ◽  
Author(s):  
Yuan-Jian LIN ◽  
Jiang-Feng LIU ◽  
Tao CHEN ◽  
Bing-Xiang HUANG ◽  
Kundwa Marie Judith ◽  
...  
Keyword(s):  
Gas Permeability ◽  
Triaxial Compression ◽  
Gas Injection ◽  
Injection Pressure ◽  
Confining Pressure ◽  
Loading Path ◽  
Permeability Change ◽  
Permeability Evolution ◽  
Axial Pressure ◽  
Triaxial Cell

Abstract In this paper, a THMC (Thermal-Hydrological-Mechanical-Chemical) multi-field coupling triaxial cell was used to systematically study the evolution of gas permeability and the deformation characteristics of sandstone. The effects of confining pressure, axial pressure, and air pressure on gas permeability characteristics were fully considered in the test. The gas permeability of sandstone decreases with increasing confining pressure. When the confining pressure is low, the variation of gas permeability is greater than the variation of gas permeability at high confining pressure. The gas injection pressure has a significant effect on the gas permeability evolution of sandstone. As the gas injection pressure increases, the gas permeability of sandstone tends to decrease. At the same confining pressure, the gas permeability of the sample during the unloading path is less than the gas permeability of the sample in the loading path. When axial pressure is applied, it has a significant influence on the permeability evolution of sandstone. When the axial pressure is less than 30 MPa, the gas permeability of the sandstone increases as the axial pressure increases. At axial pressures greater than 30 MPa, the permeability decreases as the axial pressure increases. Finally, the micro-pore/fracture structure of the sample after the gas permeability test was observed using 3D X-ray CT imaging.

scholarly journals Experimental investigations of CO2 seepage behaviorin naturally fractured coal under hydro-thermal-mechanical conditions

2021 ◽  
Vol 25 (6 Part B) ◽  
pp. 4651-4658
Author(s):  
Teng Teng ◽  
Xiaoyan Zhu ◽  
Yu-Ming Wang ◽  
Chao-Yang Ren
Keyword(s):  
Gas Flow ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Experimental Investigations ◽  
Permeability Evolution ◽  
Coal Permeability ◽  
Naturally Fractured ◽  
Series Of Experiments ◽  
Fractured Coal ◽  
Increasing Temperature

Gas-flow in coal or rock is hypersensitive to the changes of temperature, confin?ing pressure and gas pressure. This paper implemented a series of experiments to observe the seepage behavior, especially the permeability evolution of CO2 in naturally fractured coal sample under coupled hydro-thermal-mechanical conditions. The experimental results show that coal permeability increases exponentially with the increasing gas pressure, and tends to be linear when the confining pressure is high. Coal permeability decreases exponentially with the increasing confining pressure. Coal permeability decreases with the increasing temperature generally, but it may bounce up when the temperature rises to high. The results provide reference for the projects of coal gas extraction and carbon dioxide geological sequestration.

scholarly journals Experimental Investigation on the Evolution of Damage and Seepage Characteristics for Red Sandstone under Thermal-mechanical Coupling Conditions

2021 ◽  
Author(s):  
Haopeng Jiang ◽  
Annan Jiang ◽  
Fengrui Zhang
Keyword(s):  
High Temperature ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Effect Of Temperature ◽  
Permeability Evolution ◽  
Red Sandstone ◽  
Permeability Characteristics ◽  
Mechanical Coupling ◽  
Coupling Conditions ◽  
Rock Stability

Abstract Rock masses in underground space usually experience the coupling of high-temperature field, stress field and seepage field, which gives them complex mechanical behavior and permeability characteristics. In order to study the mechanical properties and permeability characteristics of red sandstone under different temperature environments, a seepage test under high temperature and triaxial compression is carried out based on the RLW-2000 multi-field coupling tester. The results show that the plastic flow of red sandstone at the stress peak under the same temperature is more obvious with the increase of confining pressure. In addition, as the confining pressure gradient increases, the permeability decreases and the trend becomes slower. And the higher the operating temperature, the easier to produce seepage channels inside the rock sample. The development of fissures is rapidly developed under the effect of temperature, so the seepage channels are widened and increased, and the permeability is greatly increased. The constitutive model of rock statistical damage considering the interaction of high temperature and osmotic pressure was constructed based on the experimental data and combining theoretical methods to reveal the characteristics of permeability evolution induced by thermal damage of rocks. The research results can be used as a reference for monitoring rock stability during geological engineering projects involving thermal-seepage-stress coupling conditions.

Gas Migration in MX80 Buffer Bentonite

1996 ◽  
Vol 465 ◽  
Author(s):  
S. T. Horseman ◽  
J. F. Harrington ◽  
P. Sellin
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Pore Space ◽  
Swelling Pressure ◽  
Confining Pressure ◽  
Threshold Value ◽  
Gas Pressure ◽  
Two Phase ◽  
Injection Pump ◽  
Flow Law

ABSTRACTControlled flow-rate gas injection experiments have been performed on pre-compacted samples of KBS-3 specification M×801 buffer bentonite using helium as a safe replacement for hydrogen. By simultaneously applying a confining pressure and backpressure, specimens were isotropically-consolidated and fully water-saturated under pre-determined effective stress conditions, before injecting gas using a syringe pump. Ingoing and outgoing gas fluxes were monitored. All tests exhibited a conspicuous threshold pressure for breakthrough, somewhat larger than the sum of the swelling pressure and the backpressure. All tests showed a post-peak negative transient leading to steady-state gas flow. Using a stepped history of flow rate, the flow law was shown to be nonlinear. With the injection pump stationary (i.e. zero applied flow rate), gas pressure declined with time to a finite value. When gas flow was reestablished, the threshold value for gas breakthrough was found to be significantly lower than in virgin clay. There is strong evidence to suggest that the capillary pressure for the penetration of interparticle pore space of buffer bentonite is of such a magnitude that normal two-phase flow is impossible. Gas entry and breakthrough is therefore accompanied by the development of microcracks which propagate through the clay from gas source to sink. The experiments suggest that these pathways open under high gas pressure conditions and partially close if gas pressure falls, providing a possible explanation of the nonlinearity of the flow law.

scholarly journals Experimental Investigation on Permeability Evolution of Dolomite Caprock under Triaxial Compression

Energies ◽  
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.

scholarly journals Experimental Study on the Shear Strength of Cement-Sand-Gravel Material

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Jie Yang ◽  
Xin Cai ◽  
Qiong Pang ◽  
Xing-wen Guo ◽  
Ying-li Wu ◽  
...  
Keyword(s):  
Experimental Study ◽  
Shear Strength ◽  
Triaxial Compression ◽  
Strength Criterion ◽  
Confining Pressure ◽  
Strength Development ◽  
Compression Tests ◽  
Aggregate Gradation ◽  
Aggregate Content ◽  
Cementing Agent

An experimental study on the shear strength development of cement-sand-gravel (CSG) material was carried out using triaxial compression tests. The effects of the cementing agent content, aggregate content, and gradation on the shear strength of CSG material were analyzed. The shear strength remarkably increased with increasing cementing agent content and aggregate content for a given confining pressure. The increase in shear strength with increasing cementing agent content far exceeded that with increasing aggregate content. However, the stress-strain curves and shear strength changed only slightly when the aggregate gradation for CSG material was adjusted. Based on the test data, a strength criterion for CSG material is proposed as a function of the cementing agent content, aggregate content, and shear strength of the aggregate gradation.

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

Geofluids ◽  
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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