Abstract Hydraulic fracture (HF) unavoidably encounters natural pre-existing discontinuities in geologic formations, which complicates the propagation and containment behavior across a discontinuity. This study explored the HF propagation across an orthogonal discontinuity in layered formations by exploiting the photoelastic, transparent, soft (or deformable), and viscoelastic characteristics of gelatin. First, photoelastic HF experiments in homogeneous gelatin media were carried out while monitoring the fluid pressure and stress intensity factor (SIF). The SIF was observed to stay constant during steady-state HF propagation. Second, photoelastic HF experiments in layered gelatin media were conducted, in which biwing-type fractures encountered the bounding layers with different levels of stiffness. Two contrasting containment behaviors — crossing or dilation/arrested — were observed. The fracture crossed the discontinuity when it encountered the bounding layer with a lower toughness. By contrast, the fracture was arrested by the bounding layer and/or dilated the discontinuity, propagating along the discontinuity when the bounding layer had a greater toughness. In addition, competition between debonding of the layer interface and creating a fresh fracture in the bounding layer was found to play a significant role in fracture containment behavior. This study provides unique experimental data with photoelastic images that are comparable to analytical or numerical models. Furthermore, the results contribute to a better understanding of HF propagation and containment behaviors across a discontinuity in viscoelastic media.

中文翻译：

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在软、粘弹性层状地层中穿过正交不连续性的韧性主导的水力裂缝传播的光弹性观察

摘要 水力压裂 (HF) 不可避免地会遇到地质构造中预先存在的自然不连续性，这使得跨不连续性的传播和遏制行为变得复杂。本研究利用明胶的光弹性、透明、柔软（或可变形）和粘弹性特性，探索了 HF 在层状地层中正交不连续处的传播。首先，在均质明胶介质中进行光弹性 HF 实验，同时监测流体压力和应力强度因子 (SIF)。观察到 SIF 在稳态 HF 传播期间保持恒定。其次，在层状明胶介质中进行了光弹性 HF 实验，其中双翼型裂缝遇到了具有不同刚度水平的边界层。观察到两种截然不同的收容行为——穿越或扩张/逮捕。当断裂遇到韧性较低的边界层时，断裂穿过了不连续性。相比之下，当边界层具有更大的韧性时，裂缝被边界层阻止和/或扩大不连续性，沿着不连续性传播。此外，发现层界面的脱粘和在边界层中产生新裂缝之间的竞争在裂缝遏制行为中起着重要作用。这项研究提供了独特的实验数据，具有可与分析或数值模型相媲美的光弹性图像。此外，这些结果有助于更好地理解 HF 在粘弹性介质中的不连续性传播和遏制行为。