Fault Zone Architecture and Fluid Flow: Insights from Field Data and Numerical Modeling
Fault Zone Architecture and Fluid Flow: Insights from Field Data and Numerical Modeling
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DOI：
10.1029/gm113p0101
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发表时间：
2013-03
期刊：
影响因子：
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通讯作者：
J. Caine;C. Forster
中科院分区：
文献类型：
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作者：
J. Caine;C. Forster
上地壳的断层带通常由复杂的断裂网络和破碎且地球化学蚀变断层岩的离散区域组成。确定这些不同的结构不连续性中的流体流动模式和速率是一个三维问题。对一组三维离散裂缝网络模型中的流体流动进行一系列数值模拟有助于确定整个幕式变形过程中与断层相关的流体流动的主要控制参数及其相互作用。四个理想化但地质上真实的断层带建筑模型基于沿着内华达州迪克西谷斯蒂尔沃特断层带暴露收集的断裂数据以及来自格陵兰岛东部一系列正常断层带的几何数据。该模型还受到与正断层相关的机械相容裂缝网络的安德森模型的约束。使用有限元程序模拟单个断层带组件（例如断层核心和损伤带）以及完整露头比例模型域中的流体流动。组分之间的渗透率对比和组分内的渗透率各向异性被认为是与断层相关的流体流动的主要控制因素。此外，这些组件的结构和水力变化也是整个模型域规模内流动的主要控制因素。这四个模型也可以被视为单个断层带机械演化的一组快照。模型内水力参数的变化通过单个变形周期模拟每个模型的渗透结构的演变。模型结果表明，单个断层带组件的结构和水力参数的微小变化可能会对整个模型域的渗透性结构产生非常大的影响，可达五个数量级。每个断层带中裂缝孔径的闭合放大了渗透率各向异性的大小和方向，其方式与隐式模拟的变形密切相关。断层带结构的变化会导致渗透性结构发生重大变化，进而显着影响断层带内部和附近的流体通量和溶质迁移的大小和模式。在不断演化的断层带的机械强度、控制断层带管道屏障系统作为流动系统的断层带密封机制以及这些过程如何与自然断层带中的流体流动相关的背景下，讨论了从模型结果得出的推论。
Fault zones in the upper crust are typically composed of complex fracture networks and discrete zones of comminuted and geochemically altered fault rocks. Determining the patterns and rates of fluid flow in these distinct structural discontinuities is a three-dimensional problem. A series of numerical simulations of fluid flow in a set of three-dimensional discrete fracture network models aids in identifying the primary controlling parameters of fault-related fluid flow, and their interactions, throughout episodic deformation. Four idealized, but geologically realistic, fault zone architectural models are based on fracture data collected along exposures of the Stillwater Fault Zone in Dixie Valley, Nevada and geometric data from a series of normal fault zones in east Greenland. The models are also constrained by an Andersonian model for mechanically compatible fracture networks associated with normal faulting. Fluid flow in individual fault zone components, such as a fault core and damage zone, and full outcrop scale model domains are simulated using a finite element routine. Permeability contrasts between components and permeability anisotropy within components are identified as the major controlling factors in fault-related fluid flow. Additionally, the structural and hydraulic variations in these components are also major controls of flow at the scale of the full model domains. The four models can also be viewed as a set of snapshots in the mechanical evolution of a single fault zone. Changes in the hydraulic parameters within the models mimic the evolution of the permeability structure of each model through a single deformation cycle. The model results demonstrate that small changes in the architecture and hydraulic parameters of individual fault zone components can have very large impacts, up to five orders of magnitude, on the permeability structure of the full model domains. Closure of fracture apertures in each fault zone magnifies the magnitude and orientation of permeability anisotropy in ways that are closely linked to the implicitly modeled deformation. Changes in fault zone architecture can cause major changes in permeability structure that, in turn, significantly impact the magnitude and patterns of fluid flux and solute transport both within and near the fault zone. Inferences derived from the model results are discussed in the context of the mechanical strength of an evolving fault zone, fault zone sealing mechanisms which control the conduit-barrier systematics of a fault zone as a flow system, and how these processes are related to fluid flow in natural fault zones.