Abstract Heat extraction by circulating cold water through a geothermal reservoir could potentially induce earthquakes of large magnitudes. In this work, we explore the role of water injection inside a normal fault in triggering seismic slip, under different temperature and rate scenarios of fluid injection into fault damage zones. The resulted non-uniformity of thermal drawdown along the fault damage zones significantly affects the magnitude and timing of induced earthquakes. A non-dimensional expression integrating fault configuration (e.g. length and thickness) and injection condition (e.g. rate and temperature) is used to describe the relationship between the injection schedule and the resulting fault seismic slip event. As the dimensionless parameter Q D increases, suggesting a transition from heat conduction to convection, the dimensionless event timing also grows nonlinearly. The perturbation of fault stress field induced from localized thermal cooling process is pronounced, compared to decoupled hydro-mechanical scenarios. The stress field perturbation in the system due to thermal cooling is characterized through a Coulomb friction ratio analysis for evaluating the stress changes along the fault plane and a tensor-based stress perturbation analysis for quantifying the stress changes in the damage zones and host rocks. The thermal influence acting on local patches along the fault strike not only advances the timing of seismic slip, but also increases the magnitude of induced seismic events, by unloading the fault to prompt seismic rupture. The injection temperature has a significant impact on facilitating the onset of seismic slip, i.e. attempting to accelerate the timing and increase the magnitude of fault reactivation. The injection rate variation will affect the timing by changing the pore pressure field and heat transfer manner. Prior to the onset of fault reactivation, the thermal unloading response increases fault permeability by decreasing normal stress, such that more permeable channels in the fault allow fluid to diffuse. Produced plastic shear strain due to fault slip provide extra positive contributions to increased normal aperture through shear dilation, thereby the fault permeability increases significantly by around two orders of magnitude.

中文翻译：

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增强型地热系统中由热扰动引起的断层再激活

摘要 通过地热储层循环冷水提取热量可能会诱发大地震。在这项工作中，我们探讨了在流体注入断层损伤带的不同温度和速率情景下，正断层内注水在触发地震滑动中的作用。由此产生的沿断层损伤带热压降的不均匀性显着影响诱发地震的震级和时间。集成断层配置（例如长度和厚度）和注入条件（例如速率和温度）的无量纲表达式用于描述注入计划和由此产生的断层地震滑动事件之间的关系。随着无量纲参数 QD 的增加，表明从热传导到对流的转变，无量纲事件时序也非线性增长。与解耦的水力机械情景相比，由局部热冷却过程引起的断层应力场的扰动是明显的。系统中由于热冷却引起的应力场扰动的特征是通过库仑摩擦比分析来评估沿断层面的应力变化，并通过基于张量的应力扰动分析来量化损伤区和主岩中的应力变化。沿着断层走向作用在局部斑块上的热影响不仅提前了地震滑动的时间，而且通过卸载断层促使地震破裂来增加诱发地震事件的幅度。注入温度对促进地震滑动的发生有显着影响，即 试图加快时间安排并增加故障重新激活的幅度。注入速率的变化会通过改变孔隙压力场和传热方式来影响时间。在断层重新激活之前，热卸载响应通过降低正应力来增加断层渗透率，从而断层中更多的渗透性通道允许流体扩散。由于断层滑动而产生的塑性剪切应变通过剪切膨胀为增加的法向孔径提供了额外的积极贡献，从而断层渗透率显着增加了大约两个数量级。热卸载响应通过降低正应力来增加断层渗透率，这样断层中更多的可渗透通道允许流体扩散。由于断层滑动而产生的塑性剪切应变通过剪切膨胀为增加的法向孔径提供了额外的积极贡献，从而断层渗透率显着增加了大约两个数量级。热卸载响应通过降低正应力来增加断层渗透率，这样断层中更多的可渗透通道允许流体扩散。由于断层滑动而产生的塑性剪切应变通过剪切膨胀为增加的法向孔径提供了额外的积极贡献，从而断层渗透率显着增加了大约两个数量级。