Experimental research on visible seepage of sandstone fissure using digital image-based method
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摘要: 自主研发的可视化裂隙渗流试验装置,应用颜色示踪的图像数字化处理技术,在不同渗透压和法向应力分级加卸载耦合作用下,进行空间垂直角度的砂岩裂隙可视化渗流试验。通过毫秒级分帧技术捕捉裂隙渗流状态并对渗流面积色域分区,基于数字化图像技术进行二值化处理,通过图层二次叠加渲染,自识别渗流面积参数,建立渗透压与法向应力作用下的渗流面积扩散规律。研究裂隙渗流优势路径各断面的过流宽度变化特征,提出可视化渗流速度求取公式,指出渗流速度沿流径变化为骤增、骤降、均匀损耗3个阶段,建立最小断面宽度对应的峰值流速与渗透压和法向应力耦合作用下的函数模型。基于实测数据建立主渗流路径中法向应力、渗透压与雷诺数的幂函数关系,标定渗流状态的惯性作用区与黏性作用区的转变临界点,构建可视化裂隙渗流雷诺数预测模型,对裂隙渗流中真实渗流路径识别、流速矢量实时变化、流体状态判定等关键科学问题提出了新的研究理论及方法。Abstract: The visual fracture seepage test devices independently developed apply the color tracer image digital processing technology to carry out the visual seepage tests on the sandstone fractures with vertical spatial angle under the coupling effects of loading and unloading with different osmotic pressure and normal stress gradations. By means of the millisecond frame division technology, the seepage state of the crack is captured and the color domain of the seepage area is partitioned. Based on the digital image technology, the binary processing is carried out. The parameters of the seepage area are identified by double overlay of layers, and the diffusion law of the seepage area under the action of osmotic pressure and normal stress is established. The characteristics of the change of the flow width of each section along the dominant seepage path of the fracture are studied, and the formula for calculating the visual seepage velocity is put forward. It is pointed out that the seepage velocity changes along the flow diameter into three stages: sudden increase, sudden decrease and uniform loss. A functional model for the peak velocity corresponding to the minimum section width is established under the coupling action of osmotic pressure and normal stress. Based on the measured data of the main seepage path, the power function for the stress normal, osmotic pressure and Reynolds number is established, the change point of seepage state in the inertia function area and viscous effect area is calibrated, and the prediction model for Reynolds number of visualized fissure flows is formulated. The new theories and research method for the key scientific issues such as identification of real seepage in fissure seepage path, real-time change of velocity vector and determination of fluid state are put forward.
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图 7 分帧、分区、特征点提取图像示例
Figure 7. Example of image extraction by frame, partition and feature points
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图 8 渗流面积临界Ⅰ值求取示意图
Figure 8. Schematic diagram of critical Ⅰ value of contact area of fracture surface
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图 10 识别盲区与误区
Figure 10. Identification blind and misunderstanding area of seepage area
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图 15 渗流面积与法向应力、渗透压的关系
Figure 15. Relationship among seepage area and normal stress and osmotic pressure
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图 19 法向应力0.1 MPa时各断面速度关系
Figure 19. Relationship between speed section at normal stress of 0.1 MPa
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图 20 法向应力0.6 MPa时各断面速度关系图
Figure 20. Relationship between speed sections at normal stress of 0.6 MPa
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图 22 渗透压与峰值流速vmax的影响关系
Figure 22. Relationship between osmotic pressure and maximum velocity
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图 24 0.1 MPa不同渗透压下渗流路径长度与雷诺数的关系
Figure 24. Reynolds number of flow path under different osmotic pressures at normal stress of 0.1 MPa
表 1 渗流面积分类与RGB值对应表
Table 1 Classification of seepage area and values of RGB
区域命名 渗流面积分类 颜色表观 RGB数值大小反映颜色的偏向 临界 归一化 R G B Ⅰ值 Ⅰ值 1区域 有效渗流面积 液体扩散区 70~105 40~85 35~85 0.32 0.11~0.32 2区域 临界渗流面积 液体微过渡区 101~130 51~90 51~90 — 0.32~0.342 3区域 非渗流面积 液体未扩散区 131~160 90~120 90~120 0.342 0.342~0.918 
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表 2 黑白高亮二值化图
Table 2 Black and white highlighted binarization diagram
法向应力/MPa 渗透压/MPa 0.1 0.2 0.3 0.4 0.5 0.6 0.1 
0.6 
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表 3 裂隙固有渗流参数δ值
Table 3 Values of intrinsic seepage parameter of crack
法向应力/MPa 0.1 0.2 0.3 0.4 0.5 0.6 δ值 49.73 47.17 45.93 41.90 39.17 23.43
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表 4 主惯性与主黏性临界点
Table 4 Critical points of main inertia and main viscosity
临界点坐标 渗透压/MPa 0.1 0.2 0.3 0.4 0.5 0.6 x（X） 8.33 7.52 7.65 7.93 8.08 8.52 y（Re） 0.71 1.15 1.18 1.74 1.86 2.27
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表 5 雷诺数预测值的平均相对误差
Table 5 Average relative errors of predicted values of Reynolds number
法向应力/MPa 0.1 0.2 0.3 0.4 0.5 0.6 平均相对误差ε 0.2659 0.1442 0.1811 0.1872 0.2059 0.1667
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