The role of fracture branching in the evolution of fracture networks: An outcrop study of the Jurassic Navajo sandstone, southern Utah
The role of fracture branching in the evolution of fracture networks: An outcrop study of the Jurassic Navajo sandstone, southern Utah
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DOI：
10.1016/j.jsg.2022.104664
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发表时间：
2022-06
影响因子：
3.1
通讯作者：
B. Surpless;Caroline McKeighan
中科院分区：
文献类型：
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作者：
B. Surpless;Caroline McKeighan
裂缝强烈地影响地质构造的渗透性，并且由于地下的大多数裂缝低于地球物理方法的分辨率，因此预测裂缝网络的空间演化对于地下水资源、石油和天然气生产以及地热能是重要的。以往的研究人员已经确定，在稳定的应力条件下，岩性力学性质的变化会影响层状岩石中节理和裂缝的扩展，但很少有研究讨论局部应力场的不稳定性如何与岩石力学性质的变化相结合，导致裂缝分支。我们研究了美国犹他州西倾塞维尔断层下盘的东北走向裂缝，峡谷暴露出近水平的侏罗纪纳瓦霍砂岩。我们分析了现场数据，岩相数据，无人驾驶航空器（UAV）的图像记录的裂缝网络。我们还使用运动恢复结构（SfM）软件建立了一个高100 m、宽260 m的3D虚拟露头模型，以帮助我们分析裂缝网络的几何形状、强度和间距变化。数据显示，向上的裂缝分支部分地适应了裂缝强度的上升和间距规律的下降。我们认为，分支是由交叉层组内的力学行为变化和与混合模式断裂系统相关的扭曲锯齿传播的组合引发的。这些树状裂缝几何形状可能与高速地震相关裂缝传播事件相关。裂缝分支强烈影响渗透率，研究地下系统中裂缝发育的研究人员应考虑裂缝分支。
Fractures strongly influence the permeability of geologic formations, and because most fractures in the subsurface are below the resolution of geophysical methods, predicting the spatial evolution of fracture networks is important for groundwater resources, oil and gas production, and geothermal energy. Previous researchers have established that variations in lithologic mechanical properties influence the propagation of joints and fractures in layered rocks under stable stress conditions, but few studies have addressed how instabilities in local stress fields, in conjunction with variations in rock mechanical properties, lead to fracture branching.We investigate NE-striking fractures in the footwall of the west-dipping Sevier fault in Utah, USA, where canyons expose the sub-horizontal Jurassic Navajo Sandstone. We analyzed field data, petrographic data, and unmanned-aerial-vehicle (UAV) imagery to document the fracture network. We also used structure-from-motion (SfM) software to build a 3D virtual outcrop model, measuring 100 m high and 260 m wide, to aid our analysis of fracture network geometry, intensity, and spacing variations.Data reveal an up-section increase in fracture intensity and decrease in spacing regularity partly accommodated by upward fracture branching. We suggest that branching was initiated by a combination of changes in mechanical behavior within cross-bed sets and twist hackle propagation associated with mixed mode fracture systems. These tree-like fracture geometries may be associated with high-velocity, earthquake-related fracture propagation events. Fracture branching strongly influences permeability and should be considered by researchers investigating fracture development in subsurface systems.