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Rock formation control is the core of safe and efficient mining in coal mines. The high strength of the hard roof, the large breaking step distance, the wide range of influence, the strong pressure effect, and the complex mechanical behavior are a major problem in the control of the coal mine roof; Moreover, the greater the thickness of the coal seam mining, the more complex the hard overburden rock movement and breaking, and the more intense the mine pressure appears, which increases the difficulty of rock formation control. Especially after the mining of coal seams gradually enters the deep part, due to the typical "three highs" storage environment of deep rock masses, coupled with the "high strength" and "strong timeliness" characteristics of extra-thick coal seam mining, the mechanical behavior of rock formation breaking in the large space range of overburden is extremely complex, and engineering disasters are frequent, which is difficult to predict and effectively control, so higher requirements are put forward for the control of hard roofs in large spaces.
To this end, Professor Yu Bin wrote an article on "Ground Fracturing Technology and Application of Large Space Hard Roof" in the 3rd issue of the Journal of Coal Science in 2021, and explained the relevant results in detail at the special conference on "Deep Rock Mechanics and Mining Theory" with this title.
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Innovation point
(1) In view of the problem that the pre-cracking technology of the existing hard roof has a small control range and limited effect, the paper proposes for the first time a method to control the mining pressure of the stope by ground fracturing the hard roof.
(2) Based on the large-scale true triaxial fracturing test system, the law of large-scale fracture expansion is revealed, the selection criteria of surface fracturing layer position, fracturing well layout, fracturing position and fracturing flow are given, and the real-time dynamic monitoring technology of integrated microseismics above and below the well is established.
(3) The key technologies of surface fracturing for multi-stage fracturing and horizontal well volumetric fracturing of surface vertical wells are proposed, the effect of controlling mine compaction in ground fracturing hard rock formations is evaluated, the technical system of hard rock formations of coal mine ground fracturing is formed, and a new method of ground fracturing of large-space hard roof surface fracturing is opened up.
About the Author
Yu Bin, engineering expert of coal mine formation control and safe and efficient mining. He was the chief engineer of Datong Coal Mine Group, and is currently a professor and doctoral supervisor of the School of Resources and Safety of Chongqing University. Vice Chairman of China Coal Society, National Outstanding Engineer, Sun Yueqi Energy Award Winner. The person in charge of the "13th Five-Year Plan" National Key R&D Program has won 1 first prize of the National Science and Technology Progress Award (ranked 2nd) and 3 second prizes; 14 first prizes of provincial and ministerial scientific and technological progress (11 first of 1st); 50 authorized invention patents (32 firsts); published 110 papers (26 SCI searches and 39 EI searches), and published 6 monographs (all first authors).
Excerpt
The high strength of the hard roof, the large breaking step distance, and the strong effect of the mine pressure are a major problem in the control of the roof plate of the coal mine, especially when the mining conditions of the extra-thick coal seam, due to the wide range of mining disturbances, the large space hard roof is broken and unstable, resulting in more complex and strong mine pressure in the stope. Studies have shown that the mining of extra-thick coal seams with hard roofs and the breaking and instability of high thick hard rock layers are the main factors causing strong ore pressure in the stope, but the existing underground pre-cracking technology cannot be controlled.
Therefore, the method of controlling the mine pressure of the stope by ground fracturing of the hard roof plate of the coal mine is proposed, and the hydraulic fracturing test study of large true triaxial in situ specimens (2060mm×1200mm×1200mm) is carried out, which reveals the expansion form of hydraulic fracture and the stress strain evolution law of the specimen in the whole process of fracturing.
The key stratigraphic range of ground fracturing is given, and the characteristics of working surface mining level, fracturing stratum, overburden stress and fracture development are synthesized, and a theoretical model and selection criteria for determining fracturing position are established. The relationship model of fracturing area-flow-time is given, and the relationship between fracturing area and fracturing time and flow rate is obtained. The integrated microseismic monitoring technology of upper and lower microseismic wells of hydraulic fracture wells was developed, and the above research was synthesized to form a large-space hard roof surface fracturing control technology system, and the practice of vertical well and horizontal well fracturing engineering was carried out.
The results show that the ground fracturing fracture has a large expansion range, the vertical well hierarchical fracturing fracture extension length is 250,218m, the fracture width is 30~120m, the horizontal well segmented fracturing fracture extension length is 196~216m, and the fracture height is 43~50m, and the fracture expansion covers the working surface range and penetrates the fracturing target layer.
The mine pressure monitoring of the underground stope shows that the working surface is mined to the fracturing fracture expansion area, the support resistance is reduced by 21%, the coal wall fragment help rate is reduced by 23%, there is no bending and breaking phenomenon of the advanced monomer, the surrounding rock of the roadway is stable, and the fracturing control effect is good. It can be seen that the ground fracturing technology of the hard roof plate can eliminate the occurrence of strong ore pressure in the stope from the source, explore a new way of hard roof control in the coal mine field, and provide a reference for solving the control of mineral pressure disaster caused by the instability of high rock layers and high structures.
Partial picture
Characteristics of large-space rock overburden structure and ore pressure
Ground fracturing hard roof is indicated
Fracturing specimens and systems
Stress-strain curve and crack propagation during fracturing
Overburden displacement-bracket to pressure integration monitoring
The impact of the breaking of hard rock formations and the release of energy
Ground fracturing position selection affected by the adoption
Simulate crack propagation areas and expansion processes
Microseismic monitoring up and down the well
Vertical well fracturing is indicated
Ground fracturing crack propagation monitoring
Microseismic event energy cloud map
Comparison of volume fractions of gas extraction holes
Bracket to press the feature comparison
Horizontal well fracturing illustration
Ground fracturing surface detectors are arranged in relative positions
Roadway deformation monitoring
source:
YU Bin,GAO Rui,XIA Binwei,et al. Ground Fracturing Technology and Application of Large Space Hard Roof[J]. Journal of China Coal Society,2021,46(3):800-811.]
YU Bin,GAO Rui,XIA Binwei,et al. Ground fracturing technology and application of hard roof in large space[J]. Journal of China Coal Society,2021,46(3):800-811.
Editor-in-charge: Qian Xiaojing
Editor:Guo Xiaowei
Review: Chang Chen
End
Professor Yu Bin's past wonderful articles
Yu Bin,Yang Jingxuan,Liu Changyou,et al. Structural characteristics of overburden rock in large space stopes and mechanism of ore pressure[J].Journal of Coal Science,2019,44(11):3295-3307.
YU Bin,XU Gang,HUANG Zhizeng,et al. Theory and key technical framework of intelligent comprehensive discharge mining of extra-thick coal seam[J].Journal of Coal Mining,2019,44(1):42-53.
Yu Bin,Zhu Weibing,Li Zhu,et al. Mechanism of instability of distant rock overburden structure in extra-thick coal seam mining[J].Journal of Coal Science and Technology,2018,43(9):2398-2407.
YU Bin,XIA Binwei,YU Peng. Effect of fracture of hard roof on gas gushing in extra-thick coal seam comprehensive discharge[J].Journal of Coal Society,2018,43(8):2243-2249.
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