Spatiotemporal changes, faulting regimes, and source parameters of induced seismicity: A case study from The Geysers geothermal field
Spatiotemporal changes, faulting regimes, and source parameters of induced seismicity: A case study from The Geysers geothermal field
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DOI：
10.1002/2014jb011385
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发表时间：
2014-11-01
影响因子：
3.9
通讯作者：
Hartline, Craig
中科院分区：
文献类型：
--
作者：
Martinez-Garzon, Patricia;Kwiatek, Grzegorz;Hartline, Craig
研究了不同流体注入速率下诱发地震活动的时空、运动学和震源特征，以确定加州间歇泉地热田西北部诱发地震活动的主要物理机制。我们分析了一个重新定位的震源目录从地震活动性集群的应力张量方向的显着变化，以前观察到与注入率。我们发现，这些应力张量取向的变化可能与孔隙压力的增加，并在储层深度的孔隙弹性应力的相应变化。峰值注入期间的地震事件往往发生在距离注入井更远的地方，优先倾向于平行于最大水平应力方向。相反，在较低的注入率的地震活动往往在不同的方向，这表明存在一个局部故障。在注入高峰期，走滑断层机制的相对贡献增加。此外，流体注入速率的增加也与B值的减小一致。我们的观察表明，无论注入阶段，大部分诱发地震的结果从储层岩石的热断裂。然而，在峰值注入间隔期间，孔隙压力的增加可能同样是诱发地震活动的原因。通过估算储层的热扩散系数和水力扩散系数，我们确认孔隙压力的特征扩散长度远大于温度的相应长度尺度，并且与在不同注入速率期间观察到的地震活动的空间范围更一致。
The spatiotemporal, kinematic, and source characteristics of induced seismicity occurring at different fluid injection rates are investigated to determine the predominant physical mechanisms responsible for induced seismicity at the northwestern part of The Geysers geothermal field, California. We analyze a relocated hypocenter catalog from a seismicity cluster where significant variations of the stress tensor orientation were previously observed to correlate with injection rates. We find that these stress tensor orientation changes may be related to increased pore pressure and the corresponding changes in poroelastic stresses at reservoir depth. Seismic events during peak injections tend to occur at greater distances from the injection well, preferentially trending parallel to the maximum horizontal stress direction. In contrast, at lower injection rates the seismicity tends to align in a different direction which suggests the presence of a local fault. During peak injection intervals, the relative contribution of strike-slip faulting mechanisms increases. Furthermore, increases in fluid injection rates also coincide with a decrease in b values. Our observations suggest that regardless of the injection stage, most of the induced seismicity results from thermal fracturing of the reservoir rock. However, during peak injection intervals, the increase in pore pressure may likewise be responsible for the induced seismicity. By estimating the thermal and hydraulic diffusivities of the reservoir, we confirm that the characteristic diffusion length for pore pressure is much greater than the corresponding length scale for temperature and also more consistent with the spatial extent of seismicity observed during different injection rates.