A novel three-dimensional discrete fracture network model for investigating the role of aperture heterogeneity on fluid flow through fractured rock masses
A novel three-dimensional discrete fracture network model for investigating the role of aperture heterogeneity on fluid flow through fractured rock masses
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DOI：
10.1016/j.ijrmms.2019.03.014
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发表时间：
2019-04
影响因子：
7.2
通讯作者：
N. Huang;Yujing Jiang;Ri-cheng Liu;Bo Li;S. Sugimoto
中科院分区：
文献类型：
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作者：
N. Huang;Yujing Jiang;Ri-cheng Liu;Bo Li;S. Sugimoto
各向异性孔径对单条岩石裂缝水力特性的影响已经有了系统的研究，但在三维离散裂缝网络（DFNs）中，单条裂缝的孔径可变性通常可以忽略不计。本研究提出了一个具有非均匀裂缝的三维DFN模型，以估计裂缝变异性对流体流动的影响。总共生成了1280个随裂缝密度和裂缝长度增加的三维模型，并使用开发的数值程序模拟了流体在模型中的流动。研究了孔径非均质性和网络拓扑结构对三维DFNs流态和渗透率的影响。结果表明，网络拓扑结构提供了一阶几何连通性框架，非均质孔径进一步允许流体在这些连接的裂缝中选择一些最具传输性的通道。具有相同孔径的DFN模型产生了大量的中等流量区域，而具有非均匀孔径裂缝的DFN模型则产生了极低和极高的流量区域。两种模型的渗透率比普遍分布在平均机械孔径变化不大的情况下，这是由于对孔径分布有很强的依赖性。随着平均机械孔径的增大，平均渗透率比先显著增大，后趋于1.0。这样就可以定义临界力学孔径，在该孔径以上，渗透率可以使用裂缝具有相同孔径的DFN模型来正确预测；在该孔径以下，渗透率受孔径变化的影响很大，应采用裂缝具有非均匀孔径的DFN模型。
Effect of anisotropic aperture on the hydraulic properties of single rock fractures has been systematically investigated, yet the aperture variability of individual fractures in 3D discrete fracture networks (DFNs) is commonly negligible by using parallel-plate fractures. The present study proposed a 3D DFN model with fractures having heterogeneous apertures to estimate the influence of fracture variability on fluid flow. In total, a set of 1280 3D models with increasing fracture densities and fracture lengths are generated and the fluid flow through the models is simulated using a developed numerical code. The influences of aperture heterogeneity and network topology on the flow pattern and permeability of 3D DFNs are estimated. The results show that the network topology provides a first-order frame of geometrical connectivity, and the heterogeneous aperture further allows the flow to select some most transmissive channels within these connected fractures. The DFN model with identical apertures generates a large number of medium-flow rate regions whereas the DFN model with fractures having heterogeneous apertures results in extremely low- and high-flow rate regions. The permeability ratio of the two models is widely spread in terms of a small variation in the average mechanical aperture as a result of strong dependence on the aperture distribution. The average permeability ratio increases significantly first and then approaches to 1.0 with increasing the average mechanical aperture. This allows for the definition of a critical mechanical aperture, above which the permeability can be properly predicted using the DFN model with fractures having identical apertures and below which the permeability is much altered by the aperture variability and the DFN model with fractures having heterogeneous apertures should be employed.