Abstract Fault zones are key features in crystalline geothermal reservoirs or in other subsurface environments due to the fact that they act as main fluid pathways. An adequate experimental description of the evolution of permeability of a realistic microscopic fault zone under in-situ reservoir and fracture parallel flow conditions is required. To address this topic, we demonstrate a novel experimental set up (Punch-Through Shear test) that is able to generate a realistic shear zone (microfault) under in-situ reservoir conditions while simultaneously measuring permeability and dilation. Three samples of intact granite from the Odenwald (Upper Rhine Graben) were placed into a MTS 815 tri-axial compression cell, where a self-designed piston assembly punched down the inner cylinder of the sample creating the desired microfault geometry with a given offset. Permeability was measured and fracture dilation was inferred from an LVDT extensometer chain, as well as the balance of fluid volume flowing in and out of the sample. After fracture generation, the shear displacement was increased to 1.2 mm and pore pressure changes of ± 5 or ± 10 MPa were applied cyclically to simulate injection and production scenarios. Formation of a microfault increased the permeability of the granite rock by 2 to almost 3 orders of magnitude. Further shear displacement led to a small increase in permeability by a factor of 1.1 to 4.0, but permeability was reduced by a factor of 2.5 to 4 within 16 h due to compaction and fault healing. Effective pressure cycling led to reversible permeability changes. CT images showed that the fracture network is rather complex, but depicts all features commonly observed in larger scale fault zones.

中文翻译：

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使用穿通剪切试验研究花岗岩微断层的水力学特性

摘要 断层带是结晶地热储层或其他地下环境的关键特征，因为它们充当主要流体通道。在原位储层和裂缝平行流条件下，需要对真实微观断层带渗透率的演变进行充分的实验描述。为了解决这个问题，我们展示了一种新的实验装置（穿通剪切测试），它能够在原位储层条件下生成真实的剪切带（微断层），同时测量渗透率和膨胀。将来自 Odenwald（上莱茵地堑）的三个完整花岗岩样品放入 MTS 815 三轴压缩室中，其中一个自行设计的活塞组件冲下样品的内圆柱体，以给定的偏移量创建所需的微故障几何形状。测量渗透率并从 LVDT 引伸计链以及流入和流出样品的流体体积的平衡推断裂缝扩张。裂缝产生后，剪切位移增加到 1.2 mm，并循环应用± 5 或± 10 MPa 的孔隙压力变化来模拟注入和生产场景。微断层的形成使花岗岩的渗透率增加了 2 到几乎 3 个数量级。进一步的剪切位移导致渗透率小幅增加 1.1 到 4.0 倍，但由于压实和断层愈合，渗透率在 16 小时内减少了 2.5 到 4 倍。有效的压力循环导致可逆的渗透率变化。CT 图像显示裂缝网络相当复杂，但描绘了在更大规模断层带中常见的所有特征。