Abstract An unprecedented increase in earthquakes associated with hydraulic stimulation has been recognized as a major barrier to the development of enhanced geothermal systems. However, the mechanism of injection-induced seismicity remains enigmatic. Here we simulate the critical stress states of sawcut and natural fractures, and examine the fracture instabilities due to fluid injection. We shed light on fluid pressure heterogeneity, injection-induced fracture instability, acoustic emission characteristics and fracture surface evolution. We find that injection-induced fracture instability is strongly dependent on fluid pressure heterogeneity and fracture surface heterogeneity. High injection rates can induce a high fluid overpressure ratio in the sawcut fracture, promoting the rupture of fracture extending into the unpressurized area. The instability of the natural fracture is due to the near-uniform reduction in effective normal stress associated with a low fluid overpressure ratio. Our data indicate that maintaining a low fluid overpressure ratio during injection activities could confine the rupture of fracture within the pressurized area. A turning point of the total moment release may be used as a reference to optimize the fluid injection strategy. The seismic response of rock fracture could be modified by changing fluid pathways between the injection borehole and the fracture and by evolving surface roughness of the fracture within the stimulated volume.

中文翻译：

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花岗岩中注入驱动的断裂不稳定性：机制和意义

摘要 与水力增产相关的地震史无前例的增加已被认为是增强地热系统发展的主要障碍。然而，注入诱发地震活动的机制仍然是个谜。在这里，我们模拟锯切和天然裂缝的临界应力状态，并检查由于流体注入引起的裂缝不稳定性。我们阐明了流体压力非均质性、注入引起的裂缝不稳定性、声发射特性和裂缝表面演化。我们发现注入引起的裂缝不稳定性强烈依赖于流体压力非均质性和裂缝表面非均质性。高注入速率会在锯切裂缝中引起高流体超压比，促进裂缝破裂延伸到未加压区域。天然裂缝的不稳定性是由于与低流体超压比相关的有效正应力几乎均匀减少。我们的数据表明，在注入活动期间保持低流体超压比可以将裂缝的破裂限制在加压区域内。总力矩释放的转折点可以作为优化流体注入策略的参考。岩石裂缝的地震响应可以通过改变注入井眼和裂缝之间的流体路径以及在受激体积内改变裂缝的表面粗糙度来修改。我们的数据表明，在注入活动期间保持低流体超压比可以将裂缝的破裂限制在加压区域内。总力矩释放的转折点可以作为优化流体注入策略的参考。岩石裂缝的地震响应可以通过改变注入井眼和裂缝之间的流体路径以及在受激体积内改变裂缝的表面粗糙度来修改。我们的数据表明，在注入活动期间保持低流体超压比可以将裂缝的破裂限制在加压区域内。总力矩释放的转折点可以作为优化流体注入策略的参考。岩石裂缝的地震响应可以通过改变注入井眼和裂缝之间的流体路径以及在受激体积内改变裂缝的表面粗糙度来修改。