a Predictive Model of Permeability for Fractal-Based Rough Rock Fractures during Shear
a Predictive Model of Permeability for Fractal-Based Rough Rock Fractures during Shear
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DOI：
10.1142/s0218348x17500517
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发表时间：
2017-09
期刊：
影响因子：
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通讯作者：
N. Huang;Yujing Jiang;Ri-cheng Liu;Bo Li;Zhenyu Zhang
中科院分区：
文献类型：
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作者：
N. Huang;Yujing Jiang;Ri-cheng Liu;Bo Li;Zhenyu Zhang
研究了裂隙粗糙度、正应力和剪切位移对三维自仿射分形岩石裂隙的渗流特性的影响，这些裂隙的表面是用改进的连续随机添加算法生成的。对粗糙岩石裂隙进行了一系列不同正应力下的数值剪切流动试验，计算了裂隙开度和渗透率的演化规律。结果表明，分形裂缝的粗糙表面可以用标度参数赫斯特指数(H)来描述，其中H=3−df，其中df是三维单个裂缝的分维。断裂断面的节理粗糙度系数(JRC)分布服从高斯函数，H与平均JRC呈负线性关系。随着剪切位移的增大，孔径分布的频率曲线由尖变平，呈现出更加各向异性和非均质性的流动形态。裂缝的平均开度和渗透率均随表面粗糙度的增大和正应力的减小而增大。在剪切开始时，渗透率显著增加，然后逐渐趋于稳定。提出了用平均机械孔径预测渗透率的模型，并与文献报道的实验结果进行了比较，验证了该模型的有效性。该模型提供了一种简单的方法来逼近基于分形的粗糙岩石裂隙在剪切过程中的渗透率，该方法可以很容易地从数字化的裂隙表面信息中获得裂隙孔径分布。
This study investigates the roles of fracture roughness, normal stress and shear displacement on the fluid flow characteristics through three-dimensional (3D) self-affine fractal rock fractures, whose surfaces are generated using the modified successive random additions (SRA) algorithm. A series of numerical shear-flow tests under different normal stresses were conducted on rough rock fractures to calculate the evolutions of fracture aperture and permeability. The results show that the rough surfaces of fractal-based fractures can be described using the scaling parameter Hurst exponent (H), in which H = 3 − Df, where Df is the fractal dimension of 3D single fractures. The joint roughness coefficient (JRC) distribution of fracture profiles follows a Gauss function with a negative linear relationship between H and average JRC. The frequency curves of aperture distributions change from sharp to flat with increasing shear displacement, indicating a more anisotropic and heterogeneous flow pattern. Both the mean aperture and permeability of fracture increase with the increment of surface roughness and decrement of normal stress. At the beginning of shear, the permeability increases remarkably and then gradually becomes steady. A predictive model of permeability using the mean mechanical aperture is proposed and the validity is verified by comparisons with the experimental results reported in literature. The proposed model provides a simple method to approximate permeability of fractal-based rough rock fractures during shear using fracture aperture distribution that can be easily obtained from digitized fracture surface information.