Six hydraulic shearing experiments have been conducted in the framework of the In-situ Stimulation and Circulation experiment within a decameter-scale crystalline rock volume at the Grimsel Test Site, Switzerland. During each experiment fractures associated with one out of two shear zone types were hydraulically reactivated. The two shear zone types differ in terms of tectonic genesis and architecture. An extensive monitoring system of sensors recording seismicity, pressure and strain was spatially distributed in 11 boreholes around the injection locations. As a result of the stimulation, the near-wellbore transmissivity increased up to 3 orders in magnitude. With one exception, jacking pressures were unchanged by the stimulations. Transmissivity change, jacking pressure and seismic activity were different for the two shear zone types, suggesting that the shear zone architectures govern the seismo-hydromechanical response. The elevated fracture fluid pressures associated with the stimulations propagated mostly along the stimulated shear zones. The absence of high-pressure signals away from the injection point for most experiments (except two out of six experiments) is interpreted as channelized flow within the shear zones. The observed deformation field within 15–20 m from the injection point is characterized by variable extensional and compressive strain produced by fracture normal opening and/or slip dislocation, as well as stress redistribution related to these processes. At greater distance from the injection location, strain measurements indicate a volumetric compressive zone, in which strain magnitudes decrease with increasing distance. These compressive strain signals are interpreted as a poro-elastic far-field response to the emplacement of fluid volume around the injection interval. Our hydromechanical data reveal that the overall stimulation effected volume is significantly larger than implied by the seismicity cloud and can be subdivided into a primary stimulated and secondary effected zone.

中文翻译：

---

流体力学过程及其对增产效果的影响：十米水力增产项目的观测

在瑞士格里姆瑟尔试验场的十米级结晶岩体中，在原位激励和循环实验框架内进行了六次水力剪切实验。在每个实验中，与两种剪切带类型之一相关的裂缝都被水力活化。两种剪切带类型在构造成因和构造上都不同。记录地震活动，压力和应变的传感器的广泛监视系统在空间上分布在注入位置周围的11个钻孔中。刺激的结果是，近井眼的透射率增加了多达三个数量级。除了一个例外，顶起压力没有受到刺激的影响。两种剪切带类型的透射率变化，顶压和地震活动都不同，这表明剪切带的结构决定了地震-水力响应。与增产相关的升高的裂缝流体压力大部分沿着增产剪切区域传播。对于大多数实验（除了六个实验中的两个实验除外），没有高压信号远离注入点被解释为剪切区内的通道化流动。从注入点开始的15–20 m范围内观察到的形变场的特征是由裂缝的正常张开和/或滑动错位以及与这些过程有关的应力重新分布所产生的可变的拉伸应变和压缩应变。在距注射位置更大的距离处，应变测量值指示一个体积压缩区，其中应变幅度随距离的增加而减小。这些压缩应变信号被解释为对在注入间隔附近的流体体积的位移的孔隙弹性远场响应。我们的流体力学数据表明，总体受地震影响的体积明显大于地震活动云所隐含的体积，并且可以细分为主要受刺激和次要影响区域。