Wang Taiyi A, Dunham Eric M
Department of Geophysics, Stanford University, Stanford, USA.
Institute for Computational and Mathematical Engineering, Stanford University, Stanford, USA.
Sci Rep. 2022 Nov 14;12(1):19481. doi: 10.1038/s41598-022-23812-7.
There is a growing recognition that subsurface fluid injection can produce not only earthquakes, but also aseismic slip on faults. A major challenge in understanding interactions between injection-related aseismic and seismic slip on faults is identifying aseismic slip on the field scale, given that most monitored fields are only equipped with seismic arrays. We present a modeling workflow for evaluating the possibility of aseismic slip, given observational constraints on the spatial-temporal distribution of microseismicity, injection rate, and wellhead pressure. Our numerical model simultaneously simulates discrete off-fault microseismic events and aseismic slip on a main fault during fluid injection. We apply the workflow to the 2012 Enhanced Geothermal System injection episode at Cooper Basin, Australia, which aimed to stimulate a water-saturated granitic reservoir containing a highly permeable ([Formula: see text] [Formula: see text]) fault zone. We find that aseismic slip likely contributed to half of the total moment release. In addition, fault weakening from pore pressure changes, not elastic stress transfer from aseismic slip, induces the majority of observed microseismic events, given the inferred stress state. We derive a theoretical model to better estimate the time-dependent spatial extent of seismicity triggered by increases in pore pressure. To our knowledge, this is the first time injection-induced aseismic slip in a granitic reservoir has been inferred, suggesting that aseismic slip could be widespread across a range of lithologies.
人们越来越认识到，地下流体注入不仅会引发地震，还会导致断层发生无震滑动。鉴于大多数监测区域仅配备了地震阵列，在理解与注入相关的断层无震滑动和地震滑动之间的相互作用时，一个主要挑战是在现场尺度上识别无震滑动。我们提出了一种建模工作流程，用于在微震时空分布、注入速率和井口压力的观测约束条件下，评估无震滑动的可能性。我们的数值模型同时模拟了流体注入过程中离散的断层外微震事件和主断层上的无震滑动。我们将该工作流程应用于2012年澳大利亚库珀盆地增强型地热系统注入事件，该事件旨在刺激一个含高渗透率（[公式：见原文][公式：见原文]）断层带的水饱和花岗岩储层。我们发现无震滑动可能占总矩释放的一半。此外，根据推断的应力状态，孔隙压力变化导致的断层弱化而非无震滑动产生的弹性应力传递引发了大部分观测到的微震事件。我们推导了一个理论模型，以更好地估计孔隙压力增加引发地震活动的时间依赖性空间范围。据我们所知，这是首次推断出花岗岩储层中注入引起的无震滑动，这表明无震滑动可能在一系列岩性中广泛存在。
