Seismic Moment Evolution During Hydraulic Stimulations
Seismic Moment Evolution During Hydraulic Stimulations
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DOI：
10.1029/2019gl086185
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发表时间：
2020-03-16
影响因子：
5.2
通讯作者：
Dresen, Georg
中科院分区：
文献类型：
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作者：
Bentz, Stephan;Kwiatek, Grzegorz;Dresen, Georg
对过去和现在的增产工程的分析表明，最大观测矩值的时间演化和增长可能与注入的流体体积和水力能量直接相关。地震矩的整体演化似乎独立于构造应力状态，而很可能受储层特定参数（如预先存在的构造库存）的支配。数据表明，震级既可以稳定增长，表明自阻断裂不断传播，也可以不受限制，最大震级仅受构造断层大小和断层连通性的限制。两种状态之间的转换可能在注射期间的任何时间发生，也可能根本不发生。增产过程中使用的监测和红绿灯系统需要从注入一开始就考虑到不稳定破裂传播的可能性，通过近实时、高分辨率地观察整个地震活动演变，以便在注入策略中立即做出反应。预测和控制流体注入引起的地震规模是目前许多与地热能源生产有关的项目关注的主要问题。在此，我们分析了迄今为止突出的地热和科学项目的震级和地震矩演化与注入参数。地震活动性的演化似乎在很大程度上与构造应力背景无关，而似乎取决于储层的具体特征。我们发现最大观测值与注入体积或水力能呈线性关系。线性关系表明，正如目前模型所预测的那样，诱发破裂的稳定增长，或者破裂的增长可能不再取决于受刺激的体积，而是取决于构造。在流体注入过程中，系统可能在这两种状态之间变化。近距离、高分辨率、近实时的地震和水力参数监测，可能有助于在充足的时间内识别这些根本变化，从而改变注入策略，控制最大震级。
Analysis of past and present stimulation projects reveals that the temporal evolution and growth of maximum observed moment magnitudes may be linked directly to the injected fluid volume and hydraulic energy. Overall evolution of seismic moment seems independent of the tectonic stress regime and is most likely governed by reservoir specific parameters, such as the preexisting structural inventory. Data suggest that magnitudes can grow either in a stable way, indicating the constant propagation of self-arrested ruptures, or unbound, for which the maximum magnitude is only limited by the size of tectonic faults and fault connectivity. Transition between the two states may occur at any time during injection or not at all. Monitoring and traffic light systems used during stimulations need to account for the possibility of unstable rupture propagation from the very beginning of injection by observing the entire seismicity evolution in near-real time and at high resolution for an immediate reaction in injection strategy.Plain Language Summary Predicting and controlling the size of earthquakes caused by fluid injection is currently the major concern of many projects associated with geothermal energy production. Here, we analyze the magnitude and seismic moment evolution with injection parameters for prominent geothermal and scientific projects to date. Evolution of seismicity seems to be largely independent of the tectonic stress background and seemingly depends on reservoir specific characteristics. We find that the maximum observed magnitudes relate linearly to the injected volume or hydraulic energy. A linear relation suggests stable growth of induced ruptures, as predicted by current models, or rupture growth may no longer depend on the stimulated volume but on tectonics. A system may change between the two states during the course of fluid injection. Close-by and high-resolution monitoring of seismic and hydraulic parameters in near-real time may help identify these fundamental changes in ample time to change injection strategy and manage maximum magnitudes.