Experimental Investigation of the Influence of the Adsorption Gas on the Permeability Characteristics of the Coal Containing Gas

2012 ◽  
Vol 616-618 ◽  
pp. 190-196
Author(s):  
Deng Ke Wang ◽  
Jian Ping Wei ◽  
Le Wei ◽  
Heng Jie Qin
Keyword(s):  
Coal Sample ◽  
Gas Adsorption ◽  
Triaxial Compression ◽  
Axial Loading ◽  
Experimental System ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Permeability Characteristics ◽  
Gas Seepage ◽  
Loading Case

A large number of laboratory experiments on the gas seepage characteristics by the self-developed gas-bearing coal triaxial compression experimental system and conducts the comparative analysis of the similarities and differences of the permeability among CO2, CH4 and N2. The results show that given the condition of constant gas pressure, the permeability of the coal sample decreases with the increase of the confining pressure; under the constant confining pressure, the permeability of the coal sample decreases with the increase of the gas pressure; gases of different adsorbabilities have different permeabilities. The stronger the gas adsorption is, the worse its permeability will be; in the axial loading case, the permeabilities of different gases all reduce firstly and increase afterward, showing the generally V-shaped variation law. The results are of certain theoretical values on the in-depth understanding of the migration law of the gas in coal seams.

scholarly journals Study on Mechanical Failure and PermeabilityCharacteristicsof Porous Gas-Bearing Coal under Triaxial Stress

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Xue-bo Zhang ◽  
Wen-yuan Wang ◽  
Ming Yang ◽  
Hang-hang Cai ◽  
Jia-jia Liu ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Elastic Modulus ◽  
Coal Sample ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Peak Strength ◽  
Triaxial Stress ◽  
Peak Strain ◽  
Permeability Characteristics ◽  
Gas Bearing

To explore the mechanical failure and permeability characteristics of porous gas-bearing coal under triaxial stress, the triaxial compression experiment was carried out for porous and conventional gas-bearing coal samples based on the triaxial creep-seepage experiment system and sound emission signal acquisition system. Acoustic emission testing was carried out at the same time of loading failure. The experimental results showed that (1) under fixed gas pressure but changing confining pressure, the porous gas-bearing coal sample had higher peak strength and elastic modulus but lower peak strain; under changing gas pressure but fixed confining pressure, the porous gas-bearing coal sample had lower peak strength and peak strain but higher elastic modulus. When either confining pressure or gas pressure was changed, the mechanical properties of the two kinds of gas-bearing coal samples showed a good consistency, but the mechanical parameters differed greatly, with the peak strength, peak strain, and elastic modulus of porous coal samples are reduced by 1/4, 2/3, and 3/4, respectively. (2) When either the confining pressure or gas pressure was changed, the permeability of the porous gas-bearing coal sample was larger than that of the conventional gas-bearing coal sample. However, the change rules of permeability characteristics of the two were basically the same, except that there was a large difference in permeability value that the porous gas-bearing coal sample increases nearly twice as much as that of the conventional gas-bearing coal sample. (3) In the whole stress-strain process, the acoustic emission characteristics of the porous gas-bearing coal sample differed significantly from those of the conventional gas-bearing coal sample. The maximum ringdown count of the porous gas-bearing coal sample can be reduced by one-third at most, the maximum energy can be reduced by nearly half at most, and the maximum amplitude changes little with only 1–3 dB reduction. The research results have important guiding significance for the prediction of failure and instability of coal tunnel and the development of relevant protective techniques.

scholarly journals Experimental study on permeability characteristics of gas-containing raw coal under different stress conditions

2018 ◽  
Vol 5 (7) ◽  
pp. 180558 ◽  
Author(s):  
Dongming Zhang ◽  
Yushun Yang ◽  
Hao Wang ◽  
Xin Bai ◽  
Chen Ye ◽  
...  
Keyword(s):  
Flow Rate ◽  
Coal Sample ◽  
Axial Stress ◽  
Axial Strain ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Permeability Characteristics ◽  
Loading And Unloading ◽  
Unloading Confining Pressure ◽  
Function Relation

The present experimental study on permeability characteristics for raw coal under different stress states is implemented by applying the triaxial self-made ‘THM coupled with servo-controlled seepage apparatus for gas-containing coal’; the result indicates that the flow rate of gas in the coal sample gradually decreases with the nonlinear loading of axial pressure and increases with the nonlinear unloading of axial stress and confining pressure. The flow rate, axial stress and confining pressure curves all satisfy the negative exponential function relation. When the sample reaches the peak intensity, the sample will be destroyed and the stress will drop rapidly; then the flow rate of the sample will increase rapidly. At this stage, the flow rate and axial strain show an oblique ‘v' pattern. The flow rate of the coal sample increases nonlinearly with the increase of gas pressure; the relation curve between flow rate and gas pressure satisfies the power function relation. Under the same confining pressure and gas pressure conditions, the larger the axial stress, the smaller the flow rate of the coal sample. Under the same axial stress and gas pressure conditions, the flow rate of the coal sample will first decrease, but then increase as the confining pressure decreases. During the post-peak loading and unloading process, the flow rate of the coal sample will decrease with the loading of confining pressure but increase with the unloading of confining pressure, and there will be an increase in wave shape with the increase in axial strain. The flow rate of each loading and unloading confining pressure is higher than that of the previous loading and unloading confining pressure. At the post-peak stage, the relation curve between the flow rate of the coal sample and the confining pressure satisfies the power function relation in the process of loading and unloading confining pressure.

scholarly journals Experimental study on the influence of aerated gas pressure and confining pressure on low-rank coal gas adsorption process

2021 ◽  
pp. 014459872110310
Author(s):  
Ming Yang ◽  
Gaini Jia ◽  
Jianliang Gao ◽  
Jiajia Liu ◽  
Xuebo Zhang ◽  
...  
Keyword(s):  
Adsorption Capacity ◽  
Coal Sample ◽  
Adsorption Process ◽  
Gas Adsorption ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Pressure Point ◽  
Adsorbed Gas ◽  
Confining Pressures ◽  
Total Adsorption

To deeply study the variation characteristics of the gas content in the process of gas adsorption for coal samples under different gas pressures and confining pressures, low-field nuclear magnetic resonance technology was used to carry out experimental research on the gas adsorption of coal. The relationship between the T2 spectrum amplitude integral and the gas quantity was analyzed. The results show the following: (1) When the samples were inflated for 11 h at each gas pressure point (0.31, 0.74, 1.11, and 1.46 MPa), after ∼5 h of adsorption, the amount of adsorbed gas exceeded 85.0% of the total adsorption capacity; additionally, as the adsorption time increased, the amount of adsorbed gas gradually tended to stabilize. When the gas pressure was >1 MPa, the amount of adsorbed gas exceeded 90.0% of the total adsorption capacity; Higher the pressure of aerated gas, greater the gas pressure gradient or concentration gradient on the surface of the coal sample and the greater the driving force for gas molecules to seep or diffuse into the coal sample. (2) When the samples were inflated for 11 h at each confining pressure point (3, 4, 5, and 7 MPa), the adsorbed gas increased by ∼85.0% of the total adsorbed gas in the first 5 h. When the pressure was <5 MPa, the amount of adsorbed gas exceeded 85.0% of the total amount of adsorption; that is, the increase in adsorbed gas was the largest at ∼5 h in the adsorption process for the columnar coal sample under different confining pressures, and the increase was ∼5.0% from 7–11 h. When the large pores in the coal sample closed, the amount of gas that seeped into the deep part of the coal sample within the same aeration time was reduced.

Gas Fractal Seepage Properties Research in Soft-Slicing Coal with Triaxial Pressure System

2013 ◽  
Vol 805-806 ◽  
pp. 1494-1501
Author(s):  
Fu Kai Zhang ◽  
Long Jun Xu ◽  
Fen Hua Yue ◽  
Xiao Qin Zhang ◽  
Yu Zhao Feng ◽  
...  
Keyword(s):  
Physical Adsorption ◽  
Experimental System ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Seepage Velocity ◽  
Adsorption Method ◽  
Pressure System ◽  
Gas Seepage ◽  
Confining Pressures ◽  
Seepage Properties

Pore structure of soft-slicing coal (SSC) is analyzed with physical adsorption method. Several experiment schemes are designed to carry out the tests of gas seepage characteristics of soft-slicing coal at the different confining pressures, gas pressures and axial pressures, with the self-developed gas seepage triaxial pressure experimental system. The typical coal from TianFu coal mine is especially sampled with different designed surface area parameters. The experiment results demonstrate the relations between the seepage velocity, the effective axial feed, and gas pressure. Under the conditions of the constant axial and confining pressure, the seepage velocity increases in an exponent way with gas pressure increasing, the permeability coefficient decreases in negative exponent, and this seepage process shows capacity fractal properties.

scholarly journals Characteristics of gas pressure change during the freezing process of gas-containing coal

2022 ◽  
pp. 014459872110731
Author(s):  
Jun Liu ◽  
Yanzhao Wei ◽  
Wei Wang ◽  
Luwei Zhang ◽  
Jinqi Wu
Keyword(s):  
Coal Sample ◽  
Gas Adsorption ◽  
Gas Pressure ◽  
Shanxi Province ◽  
Freezing Process ◽  
Rapid Decline ◽  
Freezing Response ◽  
Response Characteristics ◽  
Soft Coal ◽  
Sample Tank

To investigate the characteristics of gas pressure changes during the freezing of gas-containing composite coal, an experimental device for determining the freezing response characteristics of gas-containing coal was independently designed. Coal samples with different firmness coefficients from the No. 3 coal seam in Yuxi Coal Mine in Jincheng, Shanxi Province, were selected to determine the different freezing response characteristics. The gas pressure evolved under different temperatures (-10 °C-15 °C-20 °C-25 °C-30 °C) and different adsorption equilibrium pressures (1.0 MPa, 1.5 MPa, 2.0 MPa). The research results reveal that, during the freezing process of the gas-containing coal sample, the gas pressure in the coal sample tank changed as a monotonously decreasing function and underwent three stages: rapid decline, decline, and slow decline. The relationship between the gas pressure of the coal sample tank and the freezing time is described by a power function. Low temperatures promoted gas adsorption. As the freezing temperature decreased, the decrease of gas pressure in the coal sample tank became faster. During the freezing process, the adsorption capacity of soft coal was larger, and the gas pressure of soft coal was lower.

scholarly journals Analysis of Resistivity Anisotropy of Loaded Coal Samples

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Xiangchun Li ◽  
Zhenxing An ◽  
Qi Zhang ◽  
Xiaolong Chen ◽  
Xinwei Ye ◽  
...  
Keyword(s):  
Gas Adsorption ◽  
Structural Characteristics ◽  
Dynamic Change ◽  
Experimental System ◽  
Confining Pressure ◽  
Damage Degree ◽  
Fundamental Cause ◽  
Resistivity Anisotropy ◽  
Weak Plane ◽  
Stress Damage

In this paper, an experimental study of the variation of resistivity of coal samples in different bedding directions at 1 MHz frequency was performed by establishing an experimental system for resistivity testing of coal under triaxial stress. The low-pressure nitrogen gas adsorption (LP-N2GA) experiment and scanning electron microscopy (SEM) were obtained to analyze the pore-fracture structural characteristics of coal samples and the influence on resistivity anisotropy. Furthermore, the fundamental cause of anisotropy of coal resistivity is expounded systematically. The results show that the resistivity of loaded coal decreased first before increasing. The ionic conductance and the high degree of metamorphism slow down the decrease of resistivity. The distribution of pore and fracture structures is anisotropic. The connected pores and fractures are mainly distributed along the parallel bedding direction. The weak plane of bedding, diagenetic fractures, and plane fracture structures of parallel bedding result in the increase of fractures in the direction of vertical bedding, so increasing the potential barrier. Therefore, the resistivity in the vertical bedding direction is higher than that of the parallel bedding. Loading coal resistivity anisotropy degree is a dynamic change trend; the load increases anisotropy significantly under axial pressure, and the degree of anisotropy has a higher discreteness under confining pressure. It is mainly the randomness of the internal pore-fracture compaction, closure, and development of the heterogeneous coal under the confining pressure; the more rapid the decline in this stage, the larger the stress damage degree.

Experimental Study on Gas Pressure Effects on Gas Desorption Characteristic of Coal Seam

2013 ◽  
Vol 318 ◽  
pp. 367-370 ◽  
Author(s):  
Lin Chao Dai ◽  
Da Yong Lu ◽  
Zhen Liu
Keyword(s):  
Coal Seam ◽  
Gas Adsorption ◽  
Experimental System ◽  
Gas Pressure ◽  
Pressure Effects ◽  
Gas Content ◽  
Equilibrium Pressure ◽  
Gas Desorption ◽  
Exploitation And Utilization ◽  
The Impact

To further explore the impact of gas pressure on gas desorption and flowing law, the gas desorption experimental system designed autonomously is used to carry out studies on gas desorption experiment under different gas pressures. By data fitting, the relationship between gas desorption quantity and time is obtained and also established the model for gas desorption. The results show that: the gas desorption quantity curves is "The first half rises sharply, the latter half segment is gently rising and eventually becomes stabilized", and when the gas adsorption equilibrium pressure is the greater, the gas desorption amount is greater. And the formula can describe the gas desorption law well, the correlation coefficient R2 is above 0.97. The study provides an important theory reference to coal and gas outburst prediction, coal seam gas content prediction and its exploitation and utilization.

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.

scholarly journals Effect of Gas on Burst Proneness and Energy Dissipation of Loaded Coal: An Experimental Study Using a Novel Gas-Solid Coupling Loading Apparatus

2021 ◽  
Vol 2021 ◽  
pp. 1-21
Author(s):  
Zuguang Wang ◽  
Huamin Li ◽  
Shen Wang ◽  
Baobin Gao ◽  
Wen Wang
Keyword(s):  
Elastic Modulus ◽  
Energy Dissipation ◽  
Rock Burst ◽  
Coal Sample ◽  
Gas Adsorption ◽  
Gas Pressure ◽  
Uniaxial Loading ◽  
Gas Outburst ◽  
Coal Rock ◽  
Dynamic Disaster

Deep coal mining is seriously affected by a combined dynamic disaster of rock burst and coal and gas outburst, but the influence mechanism of gas on this combined dynamic disaster is still not very clear, which is significantly different from the single type disasters. In this study, to explore the effect of gas on the coal-rock burst, a novel gas-solid coupling loading apparatus is designed to realize gas adsorption of coal sample with burst proneness and provide uniaxial loading environment under different gas pressure. A series of uniaxial compression tests of gas-containing coal with different gas pressure is carried out, and the energy dissipation process is monitored by an acoustic emission (AE) system. Results show that the macroscopic volume strain of the coal sample increases as gas adsorption and gas pressure increase under constant uniaxial loading pressure. Gas has the ability to expand the pores and natural fractures in coal sample by mechanical and physicochemical effects, which leads to a degradation in microstructure integrity of coal sample. With the increase of gas pressure, both the macrouniaxial compression strength (UCS) and elastic modulus show a downward trend; the UCS and elastic modulus of coal samples with 2 MPa gas pressure reduce by 58.78% and 48.82%, respectively, compared to those of the original coal samples. The main reason is that gas changes the pore-fissure structure and the mesoscopic stress environment inside the coal sample. Owing to the gas, the accumulated elastic energy of the gas-containing coal samples before failure reduces significantly, whereas the energy dissipated during loading increases, and the energy release process in the postpeak stage is smoother, indicating the participation of gas weakens the burst proneness of the coal sample. This study is of important scientific value for revealing the mechanism of combined dynamic disaster and the critical occurrence conditions of coal-rock burst and coal and gas outburst.

scholarly journals Undrained monotonic triaxial loading behaviors of a type of iron ore fines

2018 ◽  
Vol 55 (9) ◽  
pp. 1349-1357 ◽  
Author(s):  
Hailong Wang ◽  
Junichi Koseki ◽  
Fei Cai ◽  
Tomoyoshi Nishimura
Keyword(s):  
Iron Ore ◽  
Initial Conditions ◽  
Triaxial Compression ◽  
Axial Loading ◽  
Sandy Soils ◽  
Peak Stress ◽  
Confining Pressure ◽  
Compression Tests ◽  
Static Liquefaction ◽  
Iron Ore Fines

Concerning the static liquefaction properties of an industrial cargo, i.e., iron ore fines (IOF), undrained monotonic behaviors of a type of IOF are revealed through conducting triaxial compression tests. It is found that IOF exhibit some similar behaviors as those of common sandy soils, while some very unusual behaviors are also observed. All IOF specimens with compaction degree of 84%–95% and confining pressure of 50–200 kPa exhibit dilative behavior from the beginning of axial loading until the deviator stresses reach their peaks (qpk). Then the dilative behavior transforms to a contractive behavior, and the contractive behavior continues until reaching the residual stress without observation of phase transformation and quasi steady state. These behaviors are not usually observed for common sandy soils based on extensive previous works. More studies may be necessary as these unusual behaviors imply that flow failure, similar to the undrained monotonic behavior of very loose sand, may be triggered regardless of the density of IOF. In addition, this study also establishes the relationships of IOF between its initial conditions, peak stress conditions, and residual conditions by employing classical knowledges developed for sandy soils.

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