Cyclic fluid injection has been demonstrated as a plausibly effective and controllable strategy to mitigate the seismic risks during hydraulic stimulation. The mechanism involved remains largely unconstrained, and our ability to control the activation of critically stressed, locally undrained faults is still limited. Injection-induced activation of these faults can be one of the most threatening scenarios as they likely perturb the stability of nearby faults beyond the stimulation volume. Here, we perform a series of laboratory fluid injection tests on critically stressed, locally undrained faults in low-permeability granite to offer insights into cyclic fluid injection as a possible solution for seismic risk mitigation. Our results show that cyclic fluid injection promotes fluid pressure diffusion on the faults, but a reduction in seismic moment release depends on several cycle-related factors, such as the critical injection pressure and injection frequency. Particularly, cyclic fluid injection could be inefficient for fluid pressure diffusion if the critical injection pressure is very close to the predicted pressure at fault failure, or over-reduced to cause excess fluid injection and long-term frictional healing. A proper design of injection parameters is thus essential to balance the energy budget between the seismic energy and hydraulic energy. Our study reveals that the effectiveness of cyclic fluid injection is also dependent on fault drainage conditions, stimulation requirements, as well as dynamic responses of faulted reservoirs, which could guide the future development of cyclic fluid injection.

循环流体注入已被证明是一种看似有效且可控的策略，可减轻水力增产过程中的地震风险。所涉及的机制在很大程度上仍然不受约束，我们控制临界应力、局部不排水断层激活的能力仍然有限。这些断层的注入引起的激活可能是最具威胁的情况之一，因为它们可能会扰乱附近断层的稳定性，超出增产体积。在这里，我们对低渗透花岗岩中的临界应力、局部不排水断层进行了一系列实验室流体注入测试提供有关循环流体注入的见解，作为减轻地震风险的可能解决方案。我们的结果表明，循环流体注入促进了断层上的流体压力扩散，但地震矩释放的减少取决于几个与循环相关的因素，例如临界注入压力和注射频率。特别是，如果临界注入压力非常接近断层故障时的预测压力，或者过度降低导致过量流体注入和长期摩擦愈合，那么循环流体注入对于流体压力扩散可能是低效的。因此，正确设计注入参数对于平衡地震能量和水力能量之间的能量预算至关重要。我们的研究表明，循环流体注入的有效性还取决于断层排水条件、增产要求以及断层储层的动态响应，这可以指导循环流体注入的未来发展。