Abstract

Fault instability in response to subsurface wastewater injection is controlled by various operation- and site-dependent parameters. Previous numerical approaches focus on the prediction of the onset of fault reactivation, whereas the subsequent stress redistribution and fault movement are not considered. To better understand the potential correlation between injection activities and fault instability, we develop a hydro-mechanical coupled finite element model and use the May 2012 Timpson earthquake sequence as a case study. Cohesive zone model integrating hyperbolic damage criterion and weakening behaviors is assigned to element interface to represent the nearby fault and capture the resulting fault behaviors under fluid injection. Simulation results indicate that this model is able to reveal the spatiotemporal evolution of pore pressure and geomechanical stress field at the Timpson site. Under continual fluid injection, pore pressure increases and gradually stabilizes, more evident in regions close to the injection layer. Poroelastic stress and pore pressure changes jointly influence the fault stability. Through damage evolution considered in the cohesive zone model, the finite element model can simulate the foreshock and main shock of the Timpson earthquake sequence, associated with fault displacement and stress relaxation. Once the damage criterion is reached, the stress redistribution at the failed fault segment induces further increase of stress on the other domains of the fault, which drives subsequent fault slip. This study brings new insights into the numerical modeling of induced earthquakes and highlights the importance of accounting for fluid injection activities to minimize the potential of fault reactivation and slip.

Article Highlights

• Hydro-mechanical model simulates pore pressure perturbation under varying injection duration, injection rate, and formation permeability.

• Progressive damage in cohesive zone elements reflects the effects of stress redistribution on fault reactivation and slip.

• The triggering of fault instability in Timpson is associated with sudden damage propagation and stress relaxations.

中文翻译：

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注入诱发断层再激活的数值分析使用具有粘性区域单元的水力-机械耦合有限元模型

摘要

响应地下废水注入的断层不稳定性由各种与操作和现场相关的参数控制。以前的数值方法侧重于预测断层重新激活的开始，而没有考虑随后的应力重新分布和断层运动。为了更好地了解注入活动与断层不稳定性之间的潜在相关性，我们开发了一个水力机械耦合有限元模型，并以 2012 年 5 月的 Timpson 地震序列作为案例研究。结合双曲线损伤准则和弱化行为的粘性带模型被分配到单元界面，以表示附近的断层并捕获流体注入下产生的断层行为。模拟结果表明，该模型能够揭示 Timpson 场地孔隙压力和地质力学应力场的时空演变。在连续流体注入下，孔隙压力增加并逐渐稳定，在靠近注入层的区域更为明显。孔隙弹性应力和孔隙压力变化共同影响断层稳定性。通过粘性带模型中考虑的损伤演化，有限元模型可以模拟与断层位移和应力松弛相关的Timpson地震序列的前震和主震。一旦达到损伤准则，失效断层段的应力重新分布会导致断层其他区域的应力进一步增加，从而驱动后续断层滑动。

文章亮点

• 流体力学模型模拟不同注入持续时间、注入速率和地层渗透率下的孔隙压力扰动。

• 粘性带单元的渐进破坏反映了应力重新分布对断层再激活和滑动的影响。

• Timpson 断层不稳定的触发与突然的损伤传播和应力松弛有关。