scholarly journals Evolution Characteristics of a High-Level Asymmetric Fracture-Seepage Community and Precise Coalbed Methane Drainage Technology during Mining of Outburst-Prone Coal Seam Groups

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Hongbing Wang ◽  
Zhiheng Cheng ◽  
Tie Li ◽  
Liang Chen ◽  
Quanle Zou ◽  
...  
Keyword(s):  
Coal Seam ◽  
Coalbed Methane ◽  
Pressure Relief ◽  
Development Zone ◽  
Coupling Relationship ◽  
Working Face ◽  
Gas Seepage ◽  
Fracture Development ◽  
Induced Fractures ◽  
Overlying Strata

The aim of this study is to explore the coupling relationship between fractures in overlying strata and gas seepage fields for pressure relief during mining of outburst-prone coal seam groups and to quantitatively characterize the distribution characteristics of favorable areas for coalbed methane (CBM) drainage in mining-induced fractures of overlying strata. For these purposes, by taking Shaqu No. 1 Coal Mine (Lvliang City, Shanxi Province, China) as a research object, this research studied migration and caving characteristics of overlying strata by combining physical similar material simulation, numerical simulation, and field measurement. Moreover, this study analyzed spatial distribution patterns of mining-induced fractures in overlaying strata, quantitatively characterized distribution parameters of asymmetric-oblique-quadrilateral fracture development zones in overlying strata, and precisely divided areas favorable for CBM drainage. On this basis, evolution laws of an asymmetric fracture-seepage community in overlying strata in outburst-prone coal seam groups were obtained, thus optimizing design parameters for directional drilling in the fracture zone in overlying strata. The research results demonstrate that, due to mining-induced influences, strata present different migration and rupture patterns along rupture lines on both sides. Because of different rupture angles α and β, mining-induced fractures in overlying strata are distributed as an asymmetric-oblique-quadrilateral fracture development body in space. Furthermore, based on the coupling relationship between fracture development states and pressure-relief gas seepage in the fracture development zone in overlying strata of the 4305 rear working face in the mine, this research obtained rupture angles α ∈ [74, 90) and ß ∈ (70, 82] on both sides of the fracture development zone. Moreover, the intervals favorable for CBM drainage for pressure relief on both sides of the fracture development zone in overlying strata of 4305 rear working face in the mine were separately determined as xaj ≤ 22.68 m and 24 m ≤ xβj ≤ 37.8 m. If the gas drainage system is designed in this zone, it is of great significance to precise and efficient pressure-relief CBM drainage in the fracture zone and ensure production safety in the mining space.

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

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.

Computational fluid dynamics optimization of gas drainage technology in gas-mining areas

2021 ◽  
pp. 014459872110635
Author(s):  
Wei Zhao ◽  
Wei Qin
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Coal Seam ◽  
Field Tests ◽  
Mining Area ◽  
Engineering Practice ◽  
Horizontal Distance ◽  
Gas Drainage ◽  
Working Face ◽  
Gas Seepage

Coal mining results in strata movement and surrounding rock failure. Eventually, manual mining space will be occupied by the destructed coal rock, making it difficult to conduct field tests of the coal seam to explore gas seepage and transport patterns. Therefore, computational fluid dynamics (CFD) numerical computation is an important tool for such studies. From the aspect of gas pre-drainage, for layer-through boreholes in the floor roadway of the 8,406 working face in Yangquan Mine 5 in China, reasonable layout parameters were obtained by CFD optimization. For effectively controlling the scope of boreholes along coal seam 9 in the Kaiyuan Mine, CFD computation was performed. The results revealed that the horizontal spacing between boreholes should be ≤2 m when a tri-quincuncial borehole layout is used. Optimization of the surface well position layout for the fault structure zone in the Xinjing Mine of the Yangquan mining area indicated that the horizontal distance between the surface well and the fault plane should be <150 m. From the aspect of gas drainage with mining-induced pressure relief, CFD computation was performed for pressure-relieved gas transport in the K8205 working face of Yangquan Mine 3. The results showed that forced roof caving should be used before the overhang length of hard roof reaches 25 m in the K8205 working face to avoid gas overrun. From the aspect of gas drainage from the abandoned gob, surface well control scopes at different surface well positions were computed, and an O-ring fissure zone is proposed as a reasonable scope for the surface well layout. CFD computation has been widely applied to coal and gas co-extraction in the Yangquan mining area and has played a significant role in guiding related gas drainage engineering practice.

scholarly journals A Mechanical Model of the Overlying Rock Masses in Undersea Coal Mining and a Stress-Seepage Coupling Numerical Simulation

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Jie Fang ◽  
Lei Tian ◽  
Yanyan Cai ◽  
Zhiguo Cao ◽  
Jinhao Wen ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Coal Seam ◽  
Coal Mining ◽  
Water Inrush ◽  
Mining Area ◽  
Analysis Model ◽  
Fractured Zones ◽  
Working Face ◽  
Seam Mining ◽  
Overlying Strata

The water inrush of a working face is the main hidden danger to the safe mining of underwater coal seams. It is known that the development of water-flowing fractured zones in overlying strata is the basic path which causes water inrushes in working faces. In the engineering background of the underwater mining in the Longkou Mining Area, the analysis model and judgment method of crack propagation were created on the basis of the Mohr–Coulomb criterion. Fish language was used to couple the extension model into the FLAC3d software, in order to simulate the mining process of the underwater coal seam, as well as to analyze the initiation evolutionary characteristics and seepage laws of the fractured zones in the overlying strata during the advancing processes of the working face. The results showed that, during the coal seam mining process, the mining fractured zones which had been caused by the compression-shear and tension-shear were mainly concentrated in the overlying strata of the working face. Also, the open-off cut and mining working face were the key sections of the water inrush in the rock mass. The condition of the water disaster was the formation of a water inrush channel. The possible water inrush channels in underwater coal mining are mainly composed of water-flowing fractured zones which are formed during the excavation processes. The numerical simulation results were validated through the practical engineering of field observations on the height of water-flowing fractured zone, which displayed a favorable adaptability.

Study on the Structure Characteristics and Ground Pressure Behavior of Overlying Strata with Shallow Buried Coal Seam

2011 ◽  
Vol 255-260 ◽  
pp. 3780-3785 ◽  
Author(s):  
Lei Yu ◽  
Zhi Zhong Fan ◽  
Gang Xu
Keyword(s):  
Coal Seam ◽  
Ground Subsidence ◽  
Mine Pressure ◽  
Structure Characteristics ◽  
Pressure Behavior ◽  
Ground Pressure ◽  
Working Face ◽  
Periodic Pressure ◽  
Seam Mining ◽  
Overlying Strata

The mine pressure behavior characters of shallow buried coal seam differed from both shallow seam mining and general depth seam. Mine pressure observation and numerical analysis were applied to research mine pressure behavior laws in fully mechanized face of shallow buried coal seam with thick bedrock and thin alluvium. It showed that the ground subsidence level phenomenon did not appear obviously although with obvious dynamic loading of fully mechanized face during the pressure period. The appearance was due to non-synchronized fracture from two key layers in the overlying rock layers and their interaction, which leaded to roof breaking initially and caving rocks with the form of an arch. Due to the periodic breaking and caving characteristics appearing as fully cut-down and arch alternately, the periodic pressure of shallow buried coal seam face showed as different size. The conclusion could be a reference for similar working face control.

scholarly journals Study on the Evolution Law of Overburden Breaking Angle under Repeated Mining and the Application of Roof Pressure Relief

Energies ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4513 ◽  
Author(s):  
Feng Cui ◽  
Tinghui Zhang ◽  
Xingping Lai ◽  
Jiantao Cao ◽  
Pengfei Shan
Keyword(s):  
Numerical Simulation ◽  
Coal Seam ◽  
Theoretical Calculation ◽  
Simulation Experiment ◽  
Elevation Angle ◽  
Theoretical Formula ◽  
Engineering Practice ◽  
Pressure Relief ◽  
Physical Similarity ◽  
Working Face

Aiming at the serious problems caused by coal mine mining activities causing the rock burst accidents, this paper is based on rock mechanics and material mechanics to establish the key layer breaking by the double-key layer beam breaking structural mechanics model of a single working face and double working face under repeated mining. The theoretical calculation formula of the angle was used as the theoretical basis for the elevation angle of the pre-reloading hole of the hard roof. The rationality and reliability of the formula were verified by the physical similarity simulation experiment and the 3 Dimension Distinct Element Code numerical simulation experiment, revealing the rock formation under the influence of repeated mining. The results show that the derived key layer breaking angle formula is suitable for the theoretical calculation of the breaking angle of the key layer of a single coal seam when the repeated disturbance coefficient is λ = 1; when it is λ = 2, it is suitable for the repeated mining of the short-distance double-coal mining. The rationality and reliability of the theoretical formula of the breaking angle of the double key layer of single coal seam and double coal seam were verified by the physical similarity simulation experiment. Through the 3DEC numerical simulation results and theoretical calculation results, the W1123 working face hard top pre-cracking pressure relief drilling elevation angle was 78°. The drilling peeping method was used to verify the results. The results show that the theoretical formula of the critical layer breaking angle is well applied in engineering practice.

Study on Mountainous Shallow-Buried Coal Seam Mining Working Face Strata Behaviors and Overlying Strata Movement Features

2011 ◽  
Vol 121-126 ◽  
pp. 2911-2916
Author(s):  
Guo Lei Liu ◽  
Ke Gong Fan ◽  
Tong Qiang Xiao
Keyword(s):  
Coal Seam ◽  
Horizontal Displacement ◽  
Simulation Software ◽  
High Rate ◽  
Strata Movement ◽  
Working Face ◽  
Element Simulation ◽  
Valve Opening ◽  
Seam Mining ◽  
Overlying Strata

Through testing the mountainous shallow-buried coal seam mining working face strata behaviors in Faer mine field, it got the strata behaviors: it was of large roof pressure, high rate of safety valve opening in hydraulic support, and even some supports crushed or took separation between top beams and tail beams. Traditional method of calculating supports’ resistance can not be applied to mountainous shallow-buried coal seam mining working face. With the discrete element simulation software UDEC it analyzed the strata movement feature, and got that the overlying strata took collapse and horizontal displacement after mountainous shallow-buried coal seam mined, and the strata movement feature was different between reverse slope mining and positive slope mining.

scholarly journals The Migration of Coalbed Methane under Mining Pressure and Air Injection: A Case Study in China

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Liqiang Zhang ◽  
Yu Wu ◽  
Hai Pu ◽  
Xiaoping He ◽  
Pan Li
Keyword(s):  
Coal Seam ◽  
Coalbed Methane ◽  
High Efficiency ◽  
Air Injection ◽  
Gas Migration ◽  
Gas Outburst ◽  
Working Face ◽  
The Matrix ◽  
Mining Pressure ◽  
And Migration

Gas outburst has always affected the safety of coal mining. To eliminate this risk by high-efficiency extraction of coalbed methane (CBM) in 4102 working face of number 3 coal seam in Hebi Number 3 coal mine, a model of CBM extraction in working face was established which was considering the mining impact of adjacent 4101 working face. In this model, the coupling relationships between stress, desorption, and migration of methane were analyzed. Moreover, we also studied the changes of methane pressure, plastic failure scope, and permeability of coal during the mining and then verified the results with the field data. And on this basis, a stimulation solution for methane extraction by injecting air into coal seam was presented, and the extraction effect was simulated. The simulation results show that the injection of air decreases the effective stress of coal which increases the permeability of coal and promotes the methane migration within the coal seam fractures. Besides, affected by the velocity of gas migration, the pressure drop between fractures and matrix will reduce with time while air injection can provide extra power for gas migration in fractures which causes the desorption and diffusion of methane in the matrix. So this stimulation solution can enhance the efficiency of gas extraction of coal seam and prevent gas outburst of the working face.

The Application of Similar Material in the Simulation of Overlying Strata Movement in High Inclined Seam in Dongbaowei Mine

2012 ◽  
Vol 600 ◽  
pp. 194-198 ◽  
Author(s):  
Ming Ming Wen
Keyword(s):  
Coal Seam ◽  
Reference Value ◽  
Geological Condition ◽  
Similar Material ◽  
Strata Movement ◽  
Support Measures ◽  
Working Face ◽  
Overlying Strata Movement ◽  
Similar Material Simulation ◽  
Overlying Strata

Studying on the characteristics of the overlying strata movement in high inclined coal seam, the similar material is applied in the simulation model which was built based on the similar material simulation theory and high inclined seam geological condition of Dongbaowei coal mine. The picture and displacement of overlying strata were obtained from the similar material simulation. As a result, the characteristics of the fracture and movement of overlying strata above the full mechanized working face in high inclined seam. This paper proposes some support measures to improve the safety of the working face. These provide significance theoretical guidance and reference value for other working face in high inclined seam.

The Research on Abutment Stress Distribution and Fracture Characteristics of Coal Seam in Longwall Face

2011 ◽  
Vol 361-363 ◽  
pp. 103-107
Author(s):  
Chuan Ming Li
Keyword(s):  
Stress Distribution ◽  
Coal Seam ◽  
Surrounding Rock ◽  
Geometrical Shape ◽  
Horizontal Distance ◽  
Site Testing ◽  
Fracture Characteristics ◽  
Working Face ◽  
Coal Wall ◽  
Overlying Strata

The abutment stress results from the load coming from overlying strata above the influence range of abutment stress and the load which coming from overlying strata above the stress shell passed by the shell. Through the mechanical calculation,this paper analyzed abutment stress distribution and fracture characteristics of coal seam resulted from the load of overlying strata passed by stress shell which exists in surrounding rock of working face, and obtained the laws of abutment stress distribution and fracture in coal seam in combination with numerical simulation and site testing. The characteristics of abutment stress distribution and fracture are related to the geometrical shape of the stress shell, such as height of the stress shell, horizontal distance between top of stress shell and coal wall,and width of stress shell skewback.

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