scholarly journals Analysis of gas migration patterns in fractured coal rocks under actual mining conditions

2017 ◽  
Vol 21 (suppl. 1) ◽  
pp. 275-284
Author(s):  
Mingzhong Gao ◽  
Ting Ai ◽  
Zhiqiang Qiu ◽  
Zetian Zhang ◽  
Jing Xie
Keyword(s):  
Coal Seam ◽  
Computer Aided Design ◽  
Gas Flow ◽  
Test Site ◽  
Fracture Network ◽  
Gas Migration ◽  
Gas Seepage ◽  
Mining Conditions ◽  
Coal Rock ◽  
Mining Face

Fracture fields in coal rocks are the main channels for gas seepage, migration, and extraction. The development, evolution, and spatial distribution of fractures in coal rocks directly affect the permeability of the coal rock as well as gas migration and flow. In this work, the Ji-15-14120 mining face at the No. 8 Coal Mine of Pingdingshan Tian?an Coal Mining Co. Ltd., Pingdingshan, China, was selected as the test site to develop a full-parameter fracture observation instrument and a dynamic fracture observation technique. The acquired video information of fractures in the walls of the boreholes was vectorized and converted to planarly expanded images on a computer-aided design platform. Based on the relative spatial distances between the openings of the boreholes, simultaneous planar images of isolated fractures in the walls of the boreholes along the mining direction were obtained from the boreholes located at various distances from the mining face. Using this information, a 3-D fracture network under mining conditions was established. The gas migration pattern was calculated using a COMSOL computation platform. The results showed that between 10 hours and 1 day the fracture network controlled the gas-flow, rather than the coal seam itself. After one day, the migration of gas was completely controlled by the fractures. The presence of fractures in the overlying rock enables the gas in coal seam to migrate more easily to the surrounding rocks or extraction tunnels situated relatively far away from the coal rock. These conclusions provide an important theoretical basis for gas extraction.

scholarly journals Field test research on gas migration law of mining coal and rock

2019 ◽  
Vol 23 (3 Part A) ◽  
pp. 1591-1597
Author(s):  
Gao-You Peng ◽  
Ming-Zhong Gao ◽  
Jing Xie ◽  
Qiang Liu ◽  
Guang-Di Deng ◽  
...  
Keyword(s):  
Gas Flow ◽  
Abutment Pressure ◽  
In Situ Monitoring ◽  
Residual Pressure ◽  
Far Field ◽  
Gas Migration ◽  
Fracture Networks ◽  
Gas Seepage ◽  
Mining Face ◽  
Migration Law

The fractures in coal and rock mass are the main channels of gas seepage, and understanding the gas migration law during mining is the precondition of gas control. The long-term in-situ monitoring of the abutment pressure, fracture networks and gas-flow in front of a mining face was carried out and the 1-D connectivity ratio of boreholes were calculated. The results showed that under the influence of mining, the fracture networks developed to the depth of rock stratum, and as far-field gas seepage channels, far-field gas continuously supplied the near-field gas. The gas flow in front of the mining face have undergone two stages of evolution from initial value to peak value, and then to a stable value. The 1-D connectivity ratio the abutment pressure about 5 to 10 m. The 1-D connectivity ratio reflected the dergree of coal and rock fracture penetration caused by mining, and the area with the highest gas extraction efficiency was the transition zone from peak abutment pressure to residual pressure in coal seams.

scholarly journals Investigation of the Flow Properties of CBM Based on Stochastic Fracture Network Modeling

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2387 ◽  
Author(s):  
Bo Zhang ◽  
Yong Li ◽  
Nicholas Fantuzzi ◽  
Yuan Zhao ◽  
Yan-Bao Liu ◽  
...  
Keyword(s):  
Coal Seam ◽  
Gas Flow ◽  
Distribution Patterns ◽  
Element Model ◽  
Fracture Network ◽  
Gas Pressure ◽  
Computational Domain ◽  
Fracture Density ◽  
Flow Properties ◽  
Fracture Network Modeling

Coal contains a large number of fractures, whose characteristics are difficult to describe in detail, while their spatial distribution patterns may follow some macroscopic statistical laws. In this paper, several fracture geometric parameters (FGPs) were used to describe a fracture, and the coal seam was represented by a two-dimensional stochastic fracture network (SFN) which was generated and processed through a series of methods in MATLAB. Then, the processed SFN image was able to be imported into COMSOL Multiphysics and converted to a computational domain through the image function. In this way, the influences of different FGPs and their distribution patterns on the permeability of the coal seam were studied, and a finite element model to investigate gas flow properties in the coal seam was carried out. The results show that the permeability of the coal seam increased with the rising of fracture density, length, aperture, and with the decrease of the angle between the fracture orientation and the gas pressure gradient. It has also been found that large-sized fractures have a more significant contribution to coal reservoir permeability. Additionally, a numerical simulation of CBM extraction was carried out to show the potential of the proposed approach in the application of tackling practical engineering problems. According to the results, not only the connectivity of fractures but also variations of gas pressure and velocity can be displayed explicitly, which is consistent well with the actual situation.

Transformation of the Triaxial Seepage Device for Measuring Deformation of Coal Containing Gas

2013 ◽  
Vol 477-478 ◽  
pp. 610-613
Author(s):  
Mei Yuan ◽  
Qing Hao Meng ◽  
Jiang Xu ◽  
Bo Bo Li ◽  
Yu Qin Du
Keyword(s):  
Coal Seam ◽  
Gas Migration ◽  
Coal Deformation ◽  
Gas Seepage

To explore the regularity of deformation and gas migration of coal seam, the author transmits signal of strain foil on coal samples in all directions by transforming oil plug, oil plug seal, heat shrink tubing and wire seal, based on the existing triaxial seepage device. We can complete coal deformation and gas seepage test with this device under different temperature, different stress, different gas stress and so on.

Research on the effect of coal seam inclination on gas migration channels at fully mechanized coal mining face

2019 ◽  
Vol 12 (18) ◽  
Author(s):  
Pengxiang Zhao ◽  
Risheng Zhuo ◽  
Shugang Li ◽  
Chun-Hsing Ho ◽  
Haifei Lin ◽  
...  
Keyword(s):  
Coal Seam ◽  
Coal Mining ◽  
Gas Migration ◽  
Mining Face

scholarly journals Effect of roof movement on gas flow in an extremely thick coal seam under fully mechanized sublevel caving mining conditions

2019 ◽  
Vol 8 (3) ◽  
pp. 677-688
Author(s):  
Haijun Guo ◽  
Xianzhang Li ◽  
Hao Cui ◽  
Kaixuan Chen ◽  
Yuanyuan Zhang
Keyword(s):  
Coal Seam ◽  
Gas Flow ◽  
Thick Coal Seam ◽  
Sublevel Caving ◽  
Mining Conditions

scholarly journals Numerical Investigation of Complex Thermal Coal-Gas Interactions in Coal-Gas Migration

2018 ◽  
Vol 2018 ◽  
pp. 1-9
Author(s):  
Xiaoyan Ni ◽  
Peng Gong ◽  
Yi Xue
Keyword(s):  
Coal Seam ◽  
Variable Temperature ◽  
Gas Pressure ◽  
Gas Migration ◽  
Coal Seams ◽  
Coal Seam Gas ◽  
Coal Gas ◽  
Thermal Coal ◽  
Gas Seepage ◽  
Gas Interactions

Understanding the influence of temperature on the gas seepage of coal seams is helpful to achieve the efficient extraction of underground coal seam gas. Thermal coal-gas interactions involve a series of complex interactions between gas and solid coal. Although the interactions between coal and gas have been studied thoroughly, few studies have considered the temperature evolution characteristics of coal seam gas extraction under the condition of variable temperature because of the complexity of the temperature effect on gas drainage. In this study, the fully coupled transient model combines the relationship of gas flow, heat transfer, coal mass deformation, and gas migration under variable temperature conditions and represents an important nonlinear response to gas migration caused by the change of effective stress. Then, this complex model is implemented into a finite element (FE) model and solved through the numerical method. Its reliability was verified by comparing with historical data. Finally, the effect of temperature on coal permeability and gas pressure is studied. The results reveal that the gas pressure in coal fracture is generally higher than that in the matrix blocks. The higher temperature of the coal seam induces the faster increase of the gas pressure. Temperature has a great effect on the gas seepage behavior in the coal seams.

Numerical Simulation of Gas Distribution and Mined Seepage Passage with the Pressure Relief of Short Distance Protective Coal Stratum

2011 ◽  
Vol 105-107 ◽  
pp. 1517-1520
Author(s):  
Yong Jun Zhang ◽  
Nian Jie Ma ◽  
Zi Min Zhang ◽  
Tian Rang Jia
Keyword(s):  
Numerical Simulation ◽  
Coal Seam ◽  
Gas Permeability ◽  
Process Analysis ◽  
Failure Process ◽  
Numerical Approach ◽  
Gas Seepage ◽  
Coal Rock ◽  
Rock Model ◽  
Stress Damage

With the full consideration of the heterogeneity, existing joints, and cracks in the rock, the coupled gas-rock model for investigating the failure process of coal-rock is established by introducing the related equations governing the evolution of stress, damage and gas permeability along with the deformation of coal and rock. A numerical approach of realistic failure process analysis (RFPA) to simulate the stratum movement, layer separation, the whole collapse progresses, and gas permeability changing of the protected coal seam is proposed. The numerical simulation results well displayed the whole processes of the cracks growth of gas seepage passage and the change of gas permeability for the closed distance protected coal seam. It can be seen from the distribution of acoustic emission in the space that the stratum failure is transferred from deeper to surface. By the analysis of the stress fields changing, the reasons of the gas permeability improvement of the protected coal seam are presented.

scholarly journals Effect of damage on gas seepage mechanism in coal seam based on a coupled model

2019 ◽  
Vol 23 (3 Part A) ◽  
pp. 1323-1328
Author(s):  
Yi Xue ◽  
Zhengzheng Cao ◽  
Faning Dang ◽  
Songhe Wang ◽  
Mingming He ◽  
...  
Keyword(s):  
Coal Seam ◽  
Gas Adsorption ◽  
Damage Model ◽  
Mechanical Damage ◽  
Coupled Model ◽  
Gas Migration ◽  
Initial Stage ◽  
Coal Deformation ◽  
Gas Seepage ◽  
Coal Damage

Damage has a significant impact on gas migration in coal seam. In this paper, a coupled hydraulic-mechanical-damage model is established, which takes into account the coupling relationship among coal damage, gas seepage and coal deformation. The simulation results show that the damage of coal body has little effect on seepage characteristic in the initial stage, but the influence of damage on gas seepage is increasing with the increase of time. Both the distribution of gas pressure and the gas adsorption content of coal body have a significant change.

scholarly journals Research and Optimization of Gas Extraction by Crossing-Seam Boreholes from Floor Roadway

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Gang Li ◽  
Jiafei Teng
Keyword(s):  
Coal Seam ◽  
Gas Permeability ◽  
Gas Pressure ◽  
Gas Content ◽  
Gas Extraction ◽  
Gas Migration ◽  
Governing Equations ◽  
Coal Seam Gas ◽  
Gas Seepage ◽  
Gas Disaster

Deep coal seams are characterized by large stress, high gas pressure, and low permeability. The gas disaster threatens the safe production of coal mine seriously. Gas extraction by crossing-seam boreholes from floor roadway (GECMBFR) can reduce the pressure and content of coal seam gas, which is the main measure to prevent gas disaster. Considering the Klinkenberg effect, governing equations of gas adsorption/desorption-diffusion, gas seepage, and stress fields within the coal seam are established to form the seepage-stress coupling model. The governing equations are embodied into a finite element driven software to numerically simulate gas migration and fluid-solid coupling law in coal seam. On this basis, the process of gas extraction under different borehole spacings and diameters is simulated. The effects of these two key parameters on coal seam gas pressure, gas content, and gas permeability were analyzed. The borehole spacing and diameter were determined to be 5 m and 0.09 m, respectively. Combined with the actual situation of a mine, the process of gas extraction from floor roadway with different cross-sectional schemes, ordinary drilling boreholes and punching combined drilling boreholes, is comparatively analyzed. The results show that the gas extraction effect by ordinary drilling boreholes is lower than that of the punching combined drilling boreholes, and the extraction is uneven and makes it difficult to meet the standard. Hydraulic punching was carried out, and coal was washed out of the borehole, which expanded the contact area between the borehole wall and coal seam. The coal seam around the punching borehole is unloaded, which improves coal permeability and accelerates gas migration towards the borehole, thus promoting the efficiency of gas extraction. It is more reasonable to use punching combined drilling borehole scheme when implementing the GECMBFR technology.

scholarly journals Numerical Simulation on the Evolution of Mining-Induced Fracture Network in a Coal Seam and Its Overburden under the Top Coal Caving Method

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Guangdi Deng ◽  
Heping Xie ◽  
Mingzhong Gao ◽  
Cong Li ◽  
Zhiqiang He
Keyword(s):  
Coal Seam ◽  
3D Modeling ◽  
Hard Rock ◽  
Fractal Theory ◽  
Soft Rock ◽  
Fracture Network ◽  
Hard Roof ◽  
Discrete Fracture ◽  
Mining Face ◽  
Overburden Strata

The evolution of the fracture network induced by mining has an important influence on the mechanical behavior of the rock and the safety of the mine. In this study, a new 3D modeling approach based on discrete fracture network (DFN) and fractal theory was developed and applied to the Tashan coal mine. The model results of the evolution of fracture in the coal seam are consistent with field observations. The evolution law of fracture network in the overburden strata was studied, and the results show that the fractal dimension of the fractures in the lower strata increased linearly and stabilized quickly within 50 m behind the mining face. In the higher strata, most of the fractures were generated behind the mining face and continued to develop farther than 100 m. More fractures were generated in the lower strata than in the higher strata, and the fractures more easily developed and expanded in the soft rock than in the hard rock. The evolution of the fractures of the main thick hard roof in the lower strata had a great impact on the generation of fractures in the higher strata.

Sign in / Sign up

Export Citation Format

Share Document