The common explanation of observed injection-induced microseismicity is based on the measured stress state at the injection interval and the assumption that it remains the same in the vicinity. We argue here that representing the stress state in different geologic formations over the injection site with the single Mohr’s circle is insufficient due to local stratigraphic features and contrast in compressibilities of the involved formations. The role of hydromechanical coupling in the microseismic response is also crucial for the proper assessment of the problem. Thoroughly monitored Illinois Basin Decatur Project revealed the majority of CO₂ injection-associated microseismic events being originated in the crystalline basement. Even though basement faults can serve as the conduits for fluid flow—the predicted pressure increase seems to be insufficient to trigger seismicity. To address this issue, accurate laboratory measurements of rock properties from the involved formations are conducted. The pre-injection stress state and its evolution are evaluated with the hydromechanically coupled numerical model. It appears that the presence of an offset in a stiff competent layer affects the stress state in its vicinity. Therefore, both the pre-injection stress state and its evolution during the fluid injection should be addressed during the induced seismicity assessment.

观测到的注入诱发的微震的常见解释是基于在注入间隔测量的应力状态以及它在附近保持不变的假设。我们在此认为，由于局部地层特征和所涉及地层的可压缩性对比，用单个莫尔圆表示注入部位上不同地质地层的应力状态是不够的。流体力学耦合在微震响应中的作用对于正确评估问题也至关重要。全面监测的伊利诺伊盆地迪凯特项目揭示了大部分 CO ₂与注入相关的微震事件起源于结晶基底。尽管基底断层可以作为流体流动的管道——预测的压力增加似乎不足以触发地震活动。为了解决这个问题，对相关地层的岩石特性进行了准确的实验室测量。使用流体力学耦合数值模型评估了注入前的应力状态及其演变。似乎在刚性主管层中存在偏移会影响其附近的应力状态。因此，在诱发地震活动评估期间，应考虑注入前应力状态及其在流体注入过程中的演变。