Experimental and Numerical Study of the Influence of Gas Pressure on Gas Permeability in Pressure Relief Gas Drainage

The permeability of coal seam is an important parameter for the gas extraction and gas outburst control. However, most of the coal seams are low-permeability with outstanding characteristic in China. Therefore，it is a good technology to provide the theoretical basis for increasing the permeability of low-gas- permeability coal seam by shocking with high-pressure air. Based on the percolation theory of porous media and combining the gas pressure change after shocking the coal seam with high-pressure air, the solid-gas coupled mathematical model is presented for the flow in the coal seam. By applying the software, the numerical simulation is computed and analyzed for the gas pressure evolution owing to the multi-spot continuous shocking the coal seam by the high-pressure air under the different pressure values and strata pressure.

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Experimental Study on the Gas Flow Characteristics and Pressure Relief Gas Drainage Effect under Different Unloading Stress Paths

Geofluids ◽

10.1155/2020/8837962 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10 ◽

Cited By ~ 1

Author(s):

Chaolin Zhang ◽

Jiang Xu ◽

Enyuan Wang ◽

Shoujian Peng

Keyword(s):

Coal Seam ◽

Gas Flow ◽

Flow Characteristics ◽

Gas Production ◽

Gas Pressure ◽

Coal Seam Gas ◽

Pressure Relief ◽

Gas Drainage ◽

Coal Temperature ◽

Drainage Effect

Coal seam gas is a critical substance because it can be a source of a large quantity of clean energy as well as a dangerous source of risk. A pressure relief gas drainage is an effective and widely used method for coal seam gas recovery and gas disaster control in coal mines. A series of pressure relief gas drainage experiments were conducted using large-scale coal samples under different unloading stress paths in this study to explore the unloading stress paths. From the experimental results, the dynamic evolutions of gas pressure, coal temperature, and gas production were analyzed. The trends of gas pressure and coal temperature during pressure relief gas drainage were similar: dropping rapidly first and then slowly with time. Correspondingly, gas production was fast in the early stage of pressure relief gas drainage and became stable thereafter. Meanwhile, gas flow characteristics were significantly affected by the unloading stress paths. Gas pressure and coal temperature had the maximum descent by unloading stress in three directions simultaneously, and the unloading stress of the Z direction had the minimal impact when only unloading in one direction of stress. However, the influence of unloading stress paths on gas production was complex and time dependent. The difference coefficient parameter was proposed to characterize the influence degree of unloading stress paths on the pressure relief gas drainage effect. Eventually, the selection of unloading stress path under different situations was discussed based on time, which is expected to provide the basis for pressure relief gas drainage.

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Coupled Effects of Stress, Moisture Content and Gas Pressure on the Permeability Evolution of Coal Samples: A Case Study of the Coking Coal Resourced from Tunlan Coalmine

Water ◽

10.3390/w13121653 ◽

2021 ◽

Vol 13 (12) ◽

pp. 1653

Author(s):

Guofu Li ◽

Yi Wang ◽

Junhui Wang ◽

Hongwei Zhang ◽

Wenbin Shen ◽

...

Keyword(s):

Moisture Content ◽

Coalbed Methane ◽

Gas Permeability ◽

Axial Stress ◽

Gas Pressure ◽

Pressure Curve ◽

Permeability Evolution ◽

Confining Stress ◽

Qinshui Basin ◽

Gas Seepage

Deep coalbed methane (CBM) is widely distributed in China and is mainly commercially exploited in the Qinshui basin. The in situ stress and moisture content are key factors affecting the permeability of CH4-containing coal samples. Therefore, considering the coupled effects of compressing and infiltrating on the gas permeability of coal could be more accurate to reveal the CH4 gas seepage characteristics in CBM reservoirs. In this study, coal samples sourced from Tunlan coalmine were employed to conduct the triaxial loading and gas seepage tests. Several findings were concluded: (1) In this triaxial test, the effect of confining stress on the permeability of gas-containing coal samples is greater than that of axial stress. (2) The permeability versus gas pressure curve of coal presents a ‘V’ shape evolution trend, in which the minimum gas permeability was obtained at a gas pressure of 1.1MPa. (3) The gas permeability of coal samples decreased exponentially with increasing moisture content. Specifically, as the moisture content increasing from 0.18% to 3.15%, the gas permeability decreased by about 70%. These results are expected to provide a foundation for the efficient exploitation of CBM in Qinshui basin.

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Permeability Enhancement Properties of High-Pressure Abrasive Water Jet Flushing and Its Application in a Soft Coal Seam

Frontiers in Energy Research ◽

10.3389/fenrg.2021.679623 ◽

2021 ◽

Vol 9 ◽

Author(s):

Xinzhe Zhang ◽

Piotr Wiśniewski ◽

Sławomir Dykas ◽

Guojie Zhang

Keyword(s):

High Pressure ◽

Coal Seam ◽

Water Jet ◽

Gas Pressure ◽

Theory And Practice ◽

Abrasive Water Jet ◽

Gas Drainage ◽

Permeability Enhancement ◽

Soft Coal ◽

Soft Coal Seam

High-pressure abrasive water jet flushing (HPAWJF) is an effective method used to improve coal seam permeability. In this study, based on the theories of gas flow and coal deformation, a coupled gas-rock model is established to investigate realistic failure processes by introducing equations for the evolution of mesoscopic element damage along with coal mass deformation. Numerical simulation of the failure and pressure relief processes is carried out under different coal seam permeability and flushing length conditions. Distributions of the seepage and gas pressure fields of the realistic failure process are analyzed. The effects of flushing permeability enhancement in a soft coal seam on the gas drainage from boreholes are revealed by conducting a field experiment. Conclusions can be extracted that the gas pressure of the slotted soft coal seam is reduced and that the gas drainage volume is three times higher than that of a conventional borehole. Field tests demonstrate that the gas drainage effect of the soft coal seam is significantly improved and that tunneling speed is nearly doubled. The results obtained from this study can provide guidance to gas drainage in soft coal seams regarding the theory and practice application of the HPAWJF method.

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Study on Dynamic Behavior of a Gas Pressure Relief Valve for a Big Flow Rate

ASME/BATH 2013 Symposium on Fluid Power and Motion Control ◽

10.1115/fpmc2013-4479 ◽

2013 ◽

Author(s):

Victor Sverbilov ◽

Dmitry Stadnick ◽

Georgy Makaryants

Keyword(s):

Flow Rate ◽

Gas Flow ◽

Dynamic Properties ◽

Gas Pressure ◽

Pressure Relief Valve ◽

Relief Valve ◽

Pressure Relief ◽

Wide Range ◽

The Impact ◽

Pilot Valve

The paper investigates instable behavior of a poppet-type gas pressure relief valve operating at a big flow rate (more than 2 kg/s) under super critical pressure drop. Instability is experienced as noise and vibration and leads to severe damage of a seat and other elements. Significant and unsteady flow forces coupled with small inherent damping make it difficult to stabilize the system. In previous works, the analytical and experimental research was carried out to reveal the most essential factors influencing stability and dynamic properties of the valve. The impact of the pilot valve dynamics on the system behavior was studied for the purpose of obtaining required accuracy and stability in a wide range of flow rate. It was shown in some testing that unstable behavior of the main valve occurred when the pilot valve was stable. This paper considers inherent stability of the main valve in the gas flow. CFD software ANSYS FLUENT is employed to study the effect of the poppet geometry on aerodynamic lifting force and valve stability in axial and lateral direction. The results have been verified through comparison with experimental data.

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The controlling effect of thick-hard igneous rock on pressure relief gas drainage and dynamic disasters in outburst coal seams

Natural Hazards ◽

10.1007/s11069-012-0547-0 ◽

2013 ◽

Vol 66 (2) ◽

pp. 1221-1241 ◽

Cited By ~ 40

Author(s):

Liang Wang ◽

Yuan-ping Cheng ◽

Chao Xu ◽

Feng-hua An ◽

Kan Jin ◽

...

Keyword(s):

Igneous Rock ◽

Coal Seams ◽

Pressure Relief ◽

Gas Drainage ◽

Controlling Effect

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Research and Application of Hydraulic Punching Pressure Relief Antireflection Mechanism in Deep “Three-Soft” Outburst Coal Seam

Shock and Vibration ◽

10.1155/2021/7241538 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Beifang Gu ◽

Yanling Wu

Keyword(s):

Coal Seam ◽

Large Scale ◽

Water Pressure ◽

Pressure Relief ◽

Gas Drainage ◽

Technical Problems ◽

Soft Coal ◽

Coal Rock ◽

Outburst Coal Seam ◽

Soft Coal Seam

To solve the problems of gas predrainage in deep seams with “three softs” and low-air permeability, hydraulic punching pressure relief antireflection technology is proposed on the basis of the research background of gas predrainage technology in Lugou Mine to alleviate technical problems, such as low gas drainage efficiency, in this mine. Through the analysis of the mechanism of hydraulic punching and coal breaking, combined with FLAC3D software, a hydraulic punching pressure relief antireflection model is established. Then, the fracture radii of coal rock are simulated and calculated. The results show that, under hydraulic punching with a water pressure of 10 MPa and coal outputs of 3 m3, 6 m3, 9 m3, and 12 m3, the fracture radii of coal and rock are 3.4 m, 4.8 m, 5.5 m, and 5.9 m, respectively. Using the software to fit the relationship between coal output V and hydraulic punching fracture radius R under the same water pressure, R = 2.32479 V0.3839 is obtained. The field test is carried out in the bottom drainage roadway of 32141 in Lugou Mine. The application effect is as follows: the gas concentration of hydraulic punching with a coal output of 3 m3 is twice that of ordinary drilling, and the coal output of hydraulic punching with a coal output of 6 m3 is four times that of ordinary drilling. The extraction concentration is four times that of ordinary drilling, and the extraction concentration of hydraulic punching with a coal output of 9 m3 is 6.4 times that of ordinary drilling. Combining the results of the numerical simulation and taking into account the actual construction situation on site, the coal output of water jetting from the borehole is 9 m3, and the fracture radius is 5.5 m. This outcome means that the effective half radius is 5.5 m, and the borehole spacing is 7.7 m. These values are the construction parameters for large-scale applications. This proposal provides effective technology and equipment for gas drainage in the deep three-soft coal seam. Consequently, it has promotion and reference significance for gas drainage in coal seam of the same geological type.

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Slotting effect on pressure relief during gas drainage of low permeability coal

Thermal Science ◽

10.2298/tsci180810222g ◽

2019 ◽

Vol 23 (3 Part A) ◽

pp. 1547-1553

Author(s):

Yanan Gao ◽

Guanghui Dong ◽

Hao Wang ◽

Xueyun Chang

Keyword(s):

In Situ Stress ◽

Gas Pressure ◽

Discontinuous Deformation Analysis ◽

Deformation Analysis ◽

Gas Drainage ◽

Mining Depth ◽

Ground Pressure ◽

Discontinuous Deformation ◽

Rheology Property

As the increase of the mining depth in China, the underground temperature, in situ stress and CH4 gas pressure also increase. Such factors have great influences on the gas drainage engineering. In this paper, the discontinuous deformation analysis is used to model the stress relief effect of drilling and slot. The effects of slot width, height, and ground pressure was analyzed. The rheology property of the coal mass under different temperature and gas pressure are also studied. the results of this paper can be used as a reference for gas drainage engineering in coal mine.

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Numerical Simulation of Borehole Parameters for Coal Seam Gas Pre-Drainage

International Journal of Heat and Technology ◽

10.18280/ijht.390432 ◽

2021 ◽

Vol 39 (4) ◽

pp. 1328-1334

Author(s):

Xiaoyan Li ◽

Jiyu Zheng ◽

Jinpin Liu

Keyword(s):

Numerical Simulation ◽

Pressure Drop ◽

Gas Pressure ◽

Borehole Diameter ◽

Gas Drainage ◽

Drainage Time ◽

Drainage Radius ◽

Simulation Results ◽

The Impact ◽

The Relationship

Borehole parameters are quite important for gas drainage. This paper studies the impact of borehole diameter and time on gas drainage and performs numerical simulation on the distribution of gas pressure under the conditions of different borehole diameters and drainage times. The simulation results reveal that, as the borehole diameter increases, the gas drainage volume increases along with it and the gas pressure decreases, but such effect on gas drainage is limited. In terms of drainage time, the longer the drainage time, the greater the drainage impact scope. Taking a gas pressure drop of 51% as the indicator of the effective pre-drainage radius, the distance from the point with a gas pressure drop of 51% to the position of the borehole is the effective pre-drainage radius. When the pre-drainage reached the 30th, 45th, 60th, 75th, and 90th day, the effective pre-drainage radius was 1.04m, 1.29m, 1.51m, 1.68m, and 1.82m respectively. According to the numerical simulation results, the effective pre-drainage radius varies with the pre-drainage time, and the fitting analysis of the two indicates that the relationship between the two can be described by a power function.

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Reasonable Scope of Kilometer Drilling in Lower Layer of Extrathick Coal Seam: A Case Study of Tingnan Coal Mine, China

Advances in Civil Engineering ◽

10.1155/2021/2044717 ◽

2021 ◽

Vol 2021 ◽

pp. 1-17

Author(s):

Delong Zou ◽

Xiang Zhang

Keyword(s):

Coal Seam ◽

Coal Mine ◽

Lower Layer ◽

Maximum Depth ◽

Support Pressure ◽

Directional Drilling ◽

Pressure Relief ◽

Gas Drainage ◽

Working Face ◽

Fracture Development

When stratified mining is adopted in high-gas and extrathick coal seam, a large amount of pressure-relief gas of the lower layer flows into the upper layer goaf along the cracks in the layer, resulting in upper layer working face to frequently exceed the gas limit. And ordinary drilling can no longer meet the requirements of the pressure-relief gas drainage of the lower layer. The 205 working face of Tingnan Coal Mine is taken as the test background in this paper, and based on the “pressure-relief and flow-increase” effect of the lower layer under the action of mining stress during the upper layer mining, the gas drainage of kilometer directional drilling in lower layer is studied. According to the distribution characteristics of support pressure before and after the working face, the pressure-relief principle, fracture development characteristics, and gas migration law of the lower layered coal body are analyzed in the process of advancing the upper layered working face in the extrathick coal seam with high gas. The maximum depth of goaf damage is calculated theoretically, and the Flac3D numerical simulation of the failure deformation of the 205 working face floor is carried out. It is found that the maximum depth of plastic failure of the lower layer is about 13 m. According to the plastic deformation of the lower layer under different vertical depths and the movement of coal and rock mass, it is determined that the reasonable range of kilometer directional drilling in the lower layer is 6–9 m below the floor vertical depth. From 15 m to 45 m in the two parallel grooves, there is no fracture failure with a sharp increase or decrease in the displacement in the local range. Meanwhile, in this part, the roof falling behind is not easy to compaction, and the displacement of the floor is large, which does not cause plastic damage. The degree of pressure relief is more sufficient, and the permeability of the lower layer is good. Therefore, drilling should be arranged as much as possible along the working face in this tendency range. The determination of reasonable arrangement range of kilometer directional drilling in extrathick coal seam provides reference index and theoretical guidance for industrial test of working face and also provides new ideas for gas control of stratified mining face in high-gas and extrathick coal seam.

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