Critical hydraulic gradient for nonlinear flow through rock fracture networks: The roles of aperture, surface roughness, and number of intersections
Critical hydraulic gradient for nonlinear flow through rock fracture networks: The roles of aperture, surface roughness, and number of intersections
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DOI：
10.1016/j.advwatres.2015.12.002
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发表时间：
2016-02
影响因子：
4.7
通讯作者：
Ri-cheng Liu;Bo Li;Yujing Jiang
中科院分区：
文献类型：
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作者：
Ri-cheng Liu;Bo Li;Yujing Jiang
当雷诺数(Re)超过某一临界值时，流体在单裂隙中从线性区域向非线性区域的转变已被证实，但离散裂隙网络(DFN)中这种转变的判据却鲜有人关注。本研究在单交叉口交叉裂缝模型上进行了渗流试验，并对不同几何特征的DFN中的流体流动进行了数值模拟。系统地研究了裂隙开度、表面粗糙度和裂隙交点数对DFN非线性渗流临界水力坡度(JC)的影响。结果表明，水力坡度(J)与流量之间的关系可以用Forchheimer定律来很好地定量，当J降到Jc以下时，通过减小非线性项，它就变成了广泛使用的立方定律。更大的孔径、更粗糙的断裂面和更多的交叉点将导致在较低的Jc处开始非线性流动。在对模拟结果进行多元回归的基础上，建立了J_c和Forchheimer定律所涉及的系数的数学表达式，这有助于在求解与裂隙网络中流体流动有关的问题时选择合适的控制方程。
Transition of fluid flow from the linear to the nonlinear regime has been confirmed in single rock fractures when the Reynolds number (Re) exceeds some critical values, yet the criterion for such a transition in discrete fracture networks (DFNs) has received little attention. This study conducted flow tests on crossed fracture models with a single intersection and performed numerical simulations on fluid flow through DFNs of various geometric characteristics. The roles of aperture, surface roughness, and number of intersections of fractures on the variation of the critical hydraulic gradient (Jc) for the onset of nonlinear flow through DFNs were systematically investigated. The results showed that the relationship between hydraulic gradient (J) and flow rate can be well quantified by Forchheimer's law; whenJdrops belowJc, it reduces to the widely used cubic law, by diminishing the nonlinear term. Larger apertures, rougher fracture surfaces, and a greater number of intersections in a DFN would result in the onset of nonlinear flow at a lowerJc. Mathematical expressions ofJcand the coefficients involved in Forchheimer's law were developed based on multi-variable regressions of simulation results, which can help to choose proper governing equations when solving problems associated with fluid flow in fracture networks.