Experimental study on freeze-thaw damage and seepage characteristics of coal rock at different prefabrication temperatures
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摘要: 为探究温度对煤岩冻融损伤及渗流特性的影响规律，采用煤岩三轴伺服实验系统对煤样进行加温、加温液氮冻融、加温饱水液氮冻融3种预处理方法开展煤岩细观损伤演化及力学、渗流特征实验。研究结果表明：预热温度越高结构损伤越严重，同一温度下饱水液氮冻融煤样的损伤大于液氮冻融煤样和仅加温煤样，损伤程度与波速呈负相关，与端面损伤合维数呈正相关；不同预处理方法下，三轴抗压强度大的煤样，破坏前变形程度小；3种预处理方法都会导致煤样内部孔裂隙增多易破碎，形成裂隙网络，煤样增透效果为加温饱水液氮冻融大于仅加温和加温液氮冻融。因此，工程实践中可探索使用预热-注水-注液氮冻融的技术实现煤层高效增透，提高瓦斯抽采效果。Abstract: This experimental study probes into the evolution patterns of fine damage and mechanical and seepage characteristics of coal rocks using the coal rock triaxial servo experiment system by employing three types of pretreatment methods, namely heating, freeze-thawing with liquid nitrogen and freeze-thawing with water, with an aim to investigate the effect of temperature on freeze-thaw damage and seepage characteristics of coal rocks.Results show that higher preheating temperature leads to more severe structural damage, damage to water-filled liquid nitrogen freeze-thawed coal samples at the same temperature is greater than that of liquid nitrogen freeze-thawed coal samples and heated coal samples only, the degree of damage is negatively correlated with the wave speed and positively correlated with the number of joint dimensions of the end face damage; coal samples with high triaxial compressive strength feature low pre-deformation under different pretreatment methods; all three pre-treatment methods lead to an increase in the number of internal pores and fractures in the coal sample, resulting in the formation of a network of fractures.Freezing and thawing the coal sample with warmed water and liquid nitrogen demonstrate more stronger effect than that of freezing and thawing with warmed liquid nitrogen only.Therefore, in engineering practice, preheating-water injection-liquid nitrogen injection freeze-thaw could be employed to achieve efficient coal seam penetration and improve the effect of gas extraction.
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Key words:
- liquid nitrogen freezing and thawing /
- triaxial loading /
- a closer look damage /
- seepage /
- translucency
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图 1 超声波探测仪及气体质量控制器设备
Figure 1. Ultrasonic detector and gas quality controller equipment
图 3 不同预热温度试件波速变化曲线
Figure 3. Wave speed variation curve of specimens with different preheating temperatures
图 5 不同温度煤样端面裂隙演化特征
Figure 5. Characterization of fracture evolution at the end face of coal samples at different temperatures
图 8 轴压加载不同温度的应力应变曲线
Figure 8. Stress-strain curves for axial compression loading at different temperatures
图 9 轴压加载相同温度的应力应变曲线
Figure 9. Stress-strain curve for axial compression loading at the same temperature
图 10 轴压加载不同温度的体积应变
Figure 10. Volume strain at different temperatures for axial compression loading
图 12 100 ℃下3种煤样加载初始及最终时刻的体积应变等值线
Figure 12. Volume strain contours of the initial and final moments of loading for three coal samples at 100 ℃
图 13 轴压加载剪切应变的综合变形程度
Figure 13. Integrated deformation degree of axial compression loaded shear strain
表 1 煤样不同预处理条件超声波特性参数
Table 1. Ultrasonic characteristic parameters of coal samples with different pretreatment conditions
处理条件 处理温度/℃ 波速v/ (km·s-1) 时间T/μs 振幅A/dB 加温 50 1.81 55.32 110.04 75 1.69 55.40 108.63 100 1.41 61.22 101.34 200 1.23 70.57 96.38 液氮冻融 50 1.54 62.36 101.12 75 1.51 63.44 93.65 100 1.35 77.38 81.26 200 1.21 78.63 97.64 饱水液氮冻融 50 1.40 80.21 85.34 75 1.23 81.48 83.12 100 1.02 82.43 80.87 200 0.83 85.19 84.36 
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表 2 煤样端面损伤参数
Table 2. Damage parameters of coal sample end face
试验条件 温度/℃ 最大裂隙宽度/mm 盒维数DB 加温 50 0.48 1.23 75 1.02 1.41 100 2.43 1.86 200 3.52 2.17 液氮冻融 50 1.16 1.55 75 1.85 1.68 100 2.92 2.04 200 3.76 2.38 饱水液氮冻融 50 1.54 1.77 75 2.17 2.05 100 3.24 2.32 200 4.25 2.69
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表 3 轴压加载剪切应变数据
Table 3. Axial compression loading shear strain
温度/℃ 实验条件 5≥a＞0 10≥b＞0 c＞10 综合变形程度A 50 加温 116 22 6 23.4 液氮冻融 105 32 7 26.8 饱水液氮冻融 92 29 23 32.3 75 加温 108 29 7 25.9 液氮冻融 93 31 20 31.7 饱水液氮冻融 78 36 30 37.2 100 加温 92 28 24 32.4 液氮冻融 83 39 22 34.9 饱水液氮冻融 57 22 65 47.0 200 加温 70 40 34 40.0 液氮冻融 64 31 49 43.3 饱水液氮冻融 48 47 49 48.1
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表 4 气体渗流量
Table 4. Gas seepage volume
实验条件 温度/℃ 轴压加载的流量/(L·min-1) 加温 50 1.23 75 2.94 100 3.54 200 9.09 液氮冻融 50 2.81 75 4.68 100 20.04 200 28.02 饱水液氮冻融 50 3.51 75 12.66 100 23.85 200 37.41
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