Impacts of coal fracture roughness and aperture on the seepage of injected water: An experimental study
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摘要:目的
煤层注水是矿井除尘、防治煤与瓦斯突出和冲击地压等灾害的关键技术措施，而裂隙粗糙度、开度等形态特征对煤层注水效果具有显著影响。
方法借助砂纸和聚酰亚胺高温胶带制备了含有不同粗糙度和开度裂隙的煤样，利用激光光谱共聚焦显微镜精准计算裂隙粗糙度参数，测试裂隙煤样渗流量。
结果和结论结果表明，表面高度偏差Ha、表面最大高度Hz和三维形貌分形维数Ds可以作为表征煤剖面粗糙程度的参数。煤体渗流量随Ha、Hz和Ds的升高呈指数降低趋势，随着剖面粗糙度从4.69提高到18.43，裂隙内的渗流量最高下降84.42%。裂隙开度在60~90 μm时其粗糙度对渗流的阻碍效果达到最高，此后粗糙单元阻碍效果开始减弱，裂隙开度在渗流过程占据主导作用。煤体渗流量随裂隙开度的升高呈指数升高的趋势，裂隙开度由30 μm提高到150 μm，裂隙渗流量最高可增大355.88倍。通过对裂隙开度和粗糙度与渗流量关系的深入探究，明确了两者在煤层注水过程中的关键作用机制，强调在煤层注水实践中应充分考虑裂隙形态特征，依据不同的裂隙开度和粗糙度情况合理选择注水方式，以实现煤层注水效果的有效提升。
Abstract:ObjectiveWater injection into coal seams is recognized as a critical technical measure for dust removal and the prevention and control of coal and gas outbursts and rock bursts in coal mines. The effectiveness of this measure is significantly influenced by the morphological characteristics of fractures, such as their roughness and aperture.
MethodsThis study prepared coal samples containing fractures with different roughness and apertures using sandpaper and polyimide tape, calculated the fracture roughness parameters accurately using a confocal laser scanning microscope (CLSM), and tested the seepage rate of fractured coal samples.
Results and ConclusionsThe results indicate that the roughness of a coal profile can be characterized using the surface height deviation (Ha), the maximum surface height (Hz), and the fractal dimension (Ds) of the 3D morphology. The seepage rate of coals decreased exponentially with an increase in Ha, Hz, and Ds. As the profile roughness increased from 4.69 to 18.43, the seepage rate of fractures decreased by up to 84.42%. In the case where fracture apertures ranged from 60 to 90 μm, the fracture roughness exhibited the most significant blocking effect on seepage. With a further increase in the fracture aperture, the blocking effect of roughness elements began to weaken, with the fracture aperture dominating the seepage process. The seepage rate of coals increased exponentially with an increase in the fracture aperture. As the fracture aperture increased from 30 μm to 150 μm, the seepage rate of fractures increased 355.88 times at most. Through a deep exploration into the relationships of the fracture aperture and roughness with seepage rate, this study determines the key mechanisms underlying the impacts of the fracture aperture and roughness on water injection into coal seams. The results suggest that it is necessary to fully consider the morphological characteristics of fractures in water injection practices. Proper water injection methods should be selected based on different fracture apertures and roughness to enhance the water injection efficiency effectively.
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图 2 砂纸及其打磨后的煤样
(a) 不同目数砂纸；(b) 砂纸打磨后的煤样
Fig. 2 Sandpaper and coal samples polished using the sandpaper
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图 4 裂隙表面测线划分位置和粗糙度曲线
Fig. 4 Survey line positions and roughness curve for a fracture surface
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图 7 裂隙表面伪彩图和粗糙度曲线
Fig. 7 Pseudo-color images and roughness curves of the fracture surfaces of various samples
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图 8 不同裂隙开度情况下分形维数、表面高度偏差、表面最大高度与渗流量的关系
Fig. 8 Relationships of fractal dimension, surface height deviation, and maximum surface height with seepage rate under different fracture apertures
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图 10 裂隙渗流流量随裂隙开度变化曲线
Fig. 10 Curves showing the seepage rate of coal fractures varying with the fracture aperture
表 1 样品信息
Table 1 Information about samples
砂纸目数 超薄胶带层数 煤样编号 36 1、2、3、4、5 S1-1、S1-2、S1-3、S1-4、S1-5 80 S2-1、S2-2、S2-3、S2-4、S2-5 120 S3-1、S3-2、S3-3、S3-4、S3-5 400 S4-1、S4-2、S4-3、S4-4、S4-5 1 200 S5-1、S5-2、S5-3、S5-4、S5-5 
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表 2 煤样裂隙表面粗糙度参数及分形维数统计
Table 2 Roughness parameters and fractal dimensions of fracture surfaces of coal samples
砂纸
目数表面高度
偏差
Ha/μm表面最大
高度
Hz/μm剖面
粗糙度
Na/μm界面扩展
面积比
Sdr/μm三维形貌
分形维数
Ds36 28.82 201.13 18.43 0.52 2.15 80 19.97 168.40 8.69 0.68 2.11 120 11.44 140.16 6.47 0.46 2.09 400 8.74 111.07 5.43 0.51 2.08 1 200 8.21 104.86 4.69 0.43 2.07
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表 3 不同粗糙度和开度裂隙的渗流量
Table 3 Seepage rates of fractures with different roughness and apertures
裂隙开度b/μm 渗流量Q/(10−9 m3·s−1) 36目 80目 120目 400目 1200 目30 0.76 0.82 0.88 0.99 1.12 60 6.93 8.89 10.42 11.32 12.78 90 32.39 38.58 42.58 47.85 53.13 120 95.13 99.46 103.33 108.04 110.18 150 271.23 273.41 275.29 276.67 277.24
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