Study on the Optimization of a Gas Drainage Borehole Drainage Horizon Based on the Evolution Characteristics of Mining Fracture
Abstract
:1. Introduction
2. Mining and Geological Conditions
3. Numerical Simulation of the Mining Fracture Evolution of the Overlying Strata in the Goaf
3.1. Model Establishment
3.2. Simulation Results and Analysis
- The fracture area of the original rock stratum: Beyond a certain distance in front of the work, the upper rock stratum is not affected by mining stress; the rock stratum has no fracture development and maintains a low permeability state.
- The fracture channel generation and development area: The overlying strata in this area gradually develops into a masonry beam structure bearing the upper strata’s pressure. The horizontal stress gradually decreases until it changes into tensile stress, and the rock fracture slowly increases.
- The fracture channel mature area: The overlying strata are completely broken and collapsed, and the strata relying on the upper masonry beam structure bear the vertical stress. The vertical stress borne by the strata here reaches its minimum state during the change of the overlying strata, and the fracture is the largest.
- The fracture channel closure area is located in the area where the goaf is recompacted. As the upper rock layer collapses further, the lower collapsed rock layer is gradually compacted. The vertical fractures in this area are gradually closed by vertical pressure. The subsidence of the overlying strata is the largest, the vertical stress of the strata is basically restored to the level before mining, and the fractures in the strata are close to the original level.
4. Analysis on Continuous Sampling of Gas Drainage Borehole Through Strata
4.1. Continuous Sampling Analysis Technology
4.2. Test Drainage Boreholes Design
4.3. Results and Analysis
- In the gas stabilization stage, before the working face is mined to the drilling section, the oxygen concentration shown in the drilling hole is basically unchanged, the cracks under the drilling hole are not connected, and the gas extracted from the drilling hole is the gas originally stored in the rock stratum (mainly methane and nitrogen).
- The gas initial change stage occurs due to the initial conduction of the fracture between the drilling hole and the goaf, and the air in the goaf flows into the upper stratum through the fracture, resulting in a sudden change in the concentration of oxygen and gas in the drilling hole.
- In the gas fluctuation stage, the gas concentration in the borehole will fluctuate due to the collapse and compaction of the rock under the borehole and the continuous generation of new cracks.
- In the gas re-stabilization stage, due to the basic end of rock activity and the completion of fracture development, the concentration of gas extracted by drilling is basically stable, and the air and methane in the goaf flow to the fractures of the upper rock stratum through drilling suction. Due to the different degrees of fracture development, the methane accumulation in different locations is different, resulting in different concentrations of gas extracted by drilling. After the completion of fracture development, the gas drainage capacity of the low-level boreholes (No. 1, No. 2, No. 4, and No. 5) is invalid, and the gas concentration is reduced to zero. The gas concentration is still very high in the high-level drilling holes (No.3 and No.6).
5. Discussion
- Distribution of the gas accumulation area formed by fracture evolution.
- 2.
- Optimization of gas drainage borehole layout.
6. Conclusions
Author Contributions
Funding
Conflicts of Interest
References
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Namber | Group Number | Drilling Depth/m | Borehole Elevation Angle/° | Horizontal Angle of Borehole/° | Vertical Height of Drilling End/m |
---|---|---|---|---|---|
1 | A | 26.1 | 35 | 0 | 15 |
2 | A | 26.9 | 45 | 0 | 19 |
3 | A | 60.0 | 37.8 | 0 | 32 |
4 | B | 26.1 | 35 | 0 | 15 |
5 | B | 26.9 | 45 | 0 | 19 |
6 | B | 60.0 | 32.5 | 0 | 23 |
Namber | Mining Time | Starting Time of Change | Duration of Initial Change/h | Duration of the Whole Process/h | Average Gas Concentration after Stabilization |
---|---|---|---|---|---|
1 | 7/13 12:19 | 7/14 5:59 | 17.67 | 43.47 | 0.96% |
2 | 7/14 7:54 | 19.58 | 85.68 | 1.57% | |
3 | 7/14 22:24 | 34.08 | 216.53 | 20.03% | |
4 | 7/16 16:30 | 7/16 20:33 | 4.05 | 8.25 | 0.24% |
5 | 7/17 2:09 | 9.65 | 49.13 | 0.49% | |
6 | 7/17 15:28 | 22.97 | 145.32 | 17.96% |
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Li, T.; Wu, B.; Lei, B. Study on the Optimization of a Gas Drainage Borehole Drainage Horizon Based on the Evolution Characteristics of Mining Fracture. Energies 2019, 12, 4499. https://doi.org/10.3390/en12234499
Li T, Wu B, Lei B. Study on the Optimization of a Gas Drainage Borehole Drainage Horizon Based on the Evolution Characteristics of Mining Fracture. Energies. 2019; 12(23):4499. https://doi.org/10.3390/en12234499
Chicago/Turabian StyleLi, Tengteng, Bing Wu, and Baiwei Lei. 2019. "Study on the Optimization of a Gas Drainage Borehole Drainage Horizon Based on the Evolution Characteristics of Mining Fracture" Energies 12, no. 23: 4499. https://doi.org/10.3390/en12234499