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.

scholarly journals Determination of Long Horizontal Borehole Height in Roofs and its Application to Gas Drainage

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2647
Author(s):  
Gang Wang ◽  
Cheng Fan ◽  
Hao Xu ◽  
Xuelin Liu ◽  
Rui Wang
Keyword(s):  
Numerical Simulation ◽  
Theoretical Model ◽  
Fracture Zone ◽  
Coalbed Methane ◽  
High Efficiency ◽  
Gas Drainage ◽  
Methane Drainage ◽  
Working Face ◽  
Variation Characteristics

Accurately determining the height of the gas-guiding fracture zone in the overlying strata of the goaf is the key to find the height of the long horizontal borehole in the roof. In order to determine the height, in this study we chose the 6306 working face of Tangkou Coal Mine in China as a research example and used both the theoretical model and discrete element method (DEM) numerical simulation to find the height of the gas-guiding fracture zone and applied the height to drill a long horizontal borehole in the roof of the 6303 working face. Furthermore, the borehole was utilized to deep into the roof for coalbed methane drainage and the results were compared with conventional gas drainage measures from other aspects. The height of the gas-guiding fracture zone was found to be 48.57 m in theoretical model based on the bulk coefficient and the void ratio and to be 51.19 m in the DEM numerical simulation according to the temporal and spatial variation characteristics of porosity. Taking both the results of theoretical analysis and numerical simulation into consideration, we determined that gas-guiding fracture zone is 49.88 m high and applied it to drill a long horizontal borehole deep into the roof in the 6303 working face field. Compared with conventional gas drainage measures, we found that the long horizontal borehole has the high stability, high efficiency and strong adaptability for methane drainage.

scholarly journals Study on the gas migration laws of non-pillar mining with gob-side entry retaining in high gas outburst coal seam

2021 ◽  
Vol 861 (5) ◽  
pp. 052058
Author(s):  
Jun Yang ◽  
Bowen Qiao ◽  
Yubing Gao ◽  
Hainan Gao ◽  
Xingjian Wei ◽  
...  
Keyword(s):  
Coal Seam ◽  
Gas Migration ◽  
Gas Outburst ◽  
Pillar Mining ◽  
Outburst Coal Seam

scholarly journals Study on Stress Distribution Law of High-Efficiency Paste Backfilling Working Face with Solid Waste in Thick Coal Seam

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Meng Zhang ◽  
Dan Fang
Keyword(s):  
Sustainable Development ◽  
Stress Distribution ◽  
Coal Seam ◽  
Solid Waste ◽  
Research Methods ◽  
High Efficiency ◽  
Distribution Law ◽  
Thick Coal Seam ◽  
The Sustainable Development ◽  
Working Face

The high-efficiency paste backfilling mining technology of solid waste in thick coal seam above 6 m is a complex system engineering, which involves mining, backfilling, supporting, subsidence, safety, and other aspects, so it is of great strategic significance to study the technology. In this paper, on the basis of comprehensive research methods such as laboratory experiments, theoretical analysis, computer programming, and other comprehensive research methods, aiming at the problems of low production capacity and high paste backfilling cost, taking the mining of No. 3 Coal Seam under buildings in Lu’an area as the research object, the stress distribution law of high-efficiency paste backfilling working face with solid waste in more than 6-meter-thick coal seam was carried out. The main achievements are as follows: On the basis of the theoretical establishment of the program method for the instability discriminant analysis of roof rock beam failure with the change of backfilling body unit strength with time, a numerical calculation model considering the change process of backfilling body strength is established. The stress distribution analysis of the E1302 working face before and during the mining process plays a guiding role in the actual production of the whole working face and roadway. The research results support the sustainable development of coal mining enterprises from technology, which has great economic, social, and environmental benefits, and can promote the industrialization of green mining high-tech in Shanxi Province and even the whole country and can promote the green mining technology progress of paste backfilling in coal mines in China, which is of great significance to the sustainable development of mining production and environmental construction.

scholarly journals Study on Law of Overlying Strata Breakage and Migration in Downward Mining of Extremely Close Coal Seams by Physical Similarity Simulation

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Xiaobin Li ◽  
Wenrui He ◽  
Zhuhe Xu
Keyword(s):  
Coal Seam ◽  
Coal Pillar ◽  
Coal Seams ◽  
Monitoring Point ◽  
Rock Stratum ◽  
Working Face ◽  
Roof Fall ◽  
And Migration ◽  
Close Coal Seams ◽  
Overlying Strata

Extremely close coal seam groups are widely distributed in China, and the main mining method is downward mining. In the downward mining process of extremely close coal seam groups, the violent movement of overlying strata will cause the redistribution of surrounding rock stress. It not only produces stress concentration on the pillar but also causes the roof of the lower coal seam to be broken and difficulty in maintaining the mining roadway. In this study, the physical similitude modeling method and field observations were used to study the breakage and migration law of overlying strata in the downward mining of extremely close coal seams. Results show that in the process of mining upper coal seam, the first weighting step of the main roof is 37.5 m and the periodic weighting step is 12.5 m. The occurrence of strata separation is beneficial to the prediction of roof weighting. When the working face advances to 25 m, the rock stratum approximating a parallelogram of height 5 m does not collapse, and the working face is relatively dangerous. When mining the lower coal seam, the overall pressure of the working face is large, but the periodic weighting of the working face is not obvious. The first collapse step of the immediate roof is 15 m. When mining the upper and lower coal seams, the subsidence of the monitoring point increases significantly at 17.5 and 15 m, respectively. The roof collapse of the lower coal seam occurs 2.5 m ahead of that of the upper coal seam. The hydraulic value of the support, roof fall height, and sloughing depth in the entire working face reach the maximum at the coal pillar, and the extreme points at the coal pillar are relatively concentrated. This research provides some guidance for the safe and efficient mining of extremely close coal seams in the future.

scholarly journals Permeability Enhancement of Coal Seam by Lower Protective Layer Mining for Gas Outburst Prevention

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Aiping He ◽  
Hua Fu ◽  
Bingjie Huo ◽  
Chaojun Fan
Keyword(s):  
Mathematical Model ◽  
Coal Seam ◽  
Stress Reduction ◽  
Protective Layer ◽  
Permeability Evolution ◽  
Layer Spacing ◽  
Gas Outburst ◽  
Permeability Enhancement ◽  
Working Face ◽  
Equivalent Layer

Risk prediction of dynamic disasters such as rock burst, gas outburst, and water inrush is closely related to the permeability evolution of coal seam. According to the characteristics of the lower protective layer mining, the basic assumption of gas-solid coupling model of the coal was proposed in this paper. The permeability enhancement coefficient of equivalent layer spacing was first put forward. Based on the three-zone-shaped dynamic evolution of the permeability of the overlying protective layer during the lower protective layer mining, the theories of seepage mechanics and damage mechanics were applied to introduce the permeability enhancement coefficient of equivalent layer spacing. A mathematical model of permeability evolution of the protected coal seam in the lower protective layer mining was established. Based on the engineering background of the lower protective layer mining in Changping Coal Mine, the numerical simulation using the proposed mathematical model was performed. The results showed that the stress and permeability of the protected layer in #3 coal seam evolved dynamically with the advancement of the working face of the protective layer in #8 coal seam. When the working face of the protective layer in #8 coal seam advanced to 80 m, the stress reduction rate in the relief area tended to be stable, and the stress in the stress reduction area was about 50% of the original rock stress. When advanced to 80 m, the permeability of the protected layer of the #3 coal seam increased sharply, and the permeability increased by 873 times. With the continuous advancement, the permeability of the protected layer in #3 coal seam tended to increase steadily, and the permeability increased by 1100–1200 times. The calculated magnitude of permeability increment is consistent with that in the engineering practice, indicating that the permeability evolution model is basically reasonable. The research provides a theoretical guidance for the gas drainage field application in the lower protective layer mining for prevention of coal and gas outburst.

scholarly journals Stability of a Roadway below a Coal Seam under Dynamic Pressure: A Case Study of the 11123 Floor Gas Drainage Roadway of a Mine in Huainan, China

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Pingsong Zhang ◽  
Yuanchao Ou ◽  
Chang Liu ◽  
Binyang Sun ◽  
Chong Xu
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Dynamic Pressure ◽  
Time Domain Reflectometry ◽  
Surrounding Rock ◽  
Monitoring Method ◽  
Gas Drainage ◽  
Gas Outburst ◽  
Working Face ◽  
Seam Mining

Coal and gas outburst is an important risk faced by coal seam mining in the Huainan region of China. In order to control gas outburst, the gas is predrained by digging a floor gas drainage roadway. To study deformation due to dynamic pressure, the failure characteristics of the floor, and their effect on the stability of the floor gas drainage roadway, a comprehensive monitoring method combining Brillouin optical time-domain reflectometry- (BOTDR-) distributed fiber optics and self-potential exploration was adopted. Dynamic data monitoring of the rock strata between the 11123 working face floor and the floor gas drainage roadway of a mine in Huainan was carried out. The field data obtained showed that, when stabilized by rock bolts and other fixed components in the surrounding rock mass of the floor gas drainage roadway, under the influence of mining, the area of concentrated stress appeared at a depth of 20.7 m, when cracks eventually formed, but the overall structural stability of the surrounding rock mass remained good. The stress distribution and crack evolution of the bottom plate under the influence of dynamic pressure showed spatiotemporal characteristics. Of these, the effect of the lead support stress was 107.48 m, and the range of effect of the hysteresis stress was 34.42 m. When the working face mining position arrives and is far from the monitoring station, the failure depth of floor rock stratum shows the following rule: unchanged in the early stage, deepened continuously in the middle stage, and finally remained stable. It takes about eight days for the dynamic adjustment of this process to finally stabilize. The results of this study can provide guidance for devising suitable procedures for carrying out intelligent green safety mining and for warning about the hazards of roadway damage.

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 Assessing the impact made by the geological features of a coalfield on producing well’s operation

2020 ◽  
Vol 7 (7) ◽  
pp. 41-48
Author(s):  
Galina I. Matniiazova ◽  
◽  
Mariia P. Khaidina ◽  
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracturing ◽  
Coal Mining ◽  
Methane Production ◽  
Coalbed Methane ◽  
Gas Production ◽  
Surrounding Rock ◽  
Gas Migration ◽  
Coalbed Methane Production ◽  
The Impact

Introduction. Coalbed methane extraction increases the economic efficiency of coal mining being a main measure mitigating coal mining risks. Research aim was to assess the impact made by host rocks with different reservoir properties on coalbed methane production dynamics before and after hydraulic fracturing. Methodology. A coal seam model has been constructed using software systems; the coal seam has been represented as an integrated deposit of two minerals, coal and gas. Gas production scenarios with and without impact on the seam have been calculated as well. A model of a coal bed with a hydraulic fracture was constructed in application program package Petrel (Shlumberger). Results. The calculation results showed the development of gas migration from the coal matrix to the surrounding rock through the fracture system during gas production. The use of hydraulic fracturing has positive impact on the dynamics of gas production from coal seams. Hydraulic fracturing revealed the growth of desorbed gas migration into the host interlayers. Analysis of coal methane migration to the surrounding rock has shown that the host rock can be considered as a transportation route for coalbed methane production.

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