The propagation paths of fluid-driven fractures in layered and faulted rocks
The propagation paths of fluid-driven fractures in layered and faulted rocks
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层状断层岩中流体驱动裂缝的扩展路径
DOI：
10.1017/s0016756822000826
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发表时间：
2022
影响因子：
2.3
通讯作者：
Agust Gudmundsson
中科院分区：
文献类型：
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作者：
Agust Gudmundsson
摘要当流体压力使岩石破裂时形成的裂缝被称为流体驱动裂缝或水力压裂。这些包括大多数堤坝，倾斜的床单和窗台，但也有许多矿脉和关节，以及人为的水力压裂。虽然相当多的领域和理论工作集中在水力压裂的几何形状和逮捕，他们如何选择自己的传播路径，特别是在层状和断层岩石，受到较少的关注。在这里，我建议所有可能的路径，一个给定的水力压裂可能遵循，它选择的路径最少（最小）的行动所确定的汉密尔顿的原则。这意味着所选择的路径是沿着其转换（释放）的能量乘以传播所花费的时间是最小的路径。水力压裂逐步推进其尖端/前缘，在裂缝前缘和流体前缘之间存在时滞。在本框架中，每个步骤由汉密尔顿原理控制。结果表明，当围岩均质、各向同性、无裂隙时，水压致裂路径处处垂直于最小压（拉）主应力σ3的轨迹，并遵循最大主压应力σ1的轨迹。当应用于层状和断层岩体时，结果表明，水力压裂路径可能会沿着现有断层走一段时间，这主要取决于（1）断层的倾角（垂直传播的水力压裂最有可能使用陡峭的断层），以及（2）与沿着沿着σ 1方向的路径的寄主岩石的拉伸强度相比，穿过断层的拉伸强度。结果表明，水力压裂可能会使用故障作为其路径的一部分，主要是如果故障是陡峭的倾角和接近零的拉伸强度。
Abstract Fractures that form when fluid pressure ruptures the rock are referred to as fluid-driven fractures or hydrofractures. These include most dykes, inclined sheets and sills, but also many mineral veins and joints, as well as human-made hydraulic fractures. While considerable field and theoretical work has focused on the geometry and arrest of hydrofractures, how they select their propagation paths, particularly in layered and faulted rocks, has received less attention. Here I propose that of all the possible paths that a given hydrofracture may follow, it selects the path of least (minimum) action as determined by Hamilton’s principle. This means that the selected path is that along which the energy transformed (released) multiplied by the time taken for the propagation is a minimum. Hydrofractures advance their tips/fronts in steps, with a time lag between the fracture front and the fluid front. In the present framework, each step is then controlled by Hamilton’s principle. The results suggest that when the hosting rock body is regarded as homogeneous, isotropic and non-fractured, hydrofracture paths are everywhere perpendicular to the trajectories of the minimum compressive (maximum tensile) principal stress σ3 and follow the trajectories of the maximum principal compressive stress σ1. When applied to layered and faulted rock body, the results indicate that hydrofracture paths may follow existing faults for a while, depending primarily on (1) the dip of the fault (steep faults are the most likely to be used by vertically propagating hydrofractures), and (2) the tensile strength across the fault compared with the tensile strength of the host rock along a path following the direction of σ 1. The results suggest that hydrofractures may use faults as parts of their paths primarily if the fault is steeply dipping and with close to zero tensile strength.