The success of geological carbon storage depends on the assurance of permanent containment for injected carbon dioxide (CO₂) in the storage formation at depth. One of the critical elements of the safekeeping of CO₂ is the sealing capacity of the caprock overlying the storage formation despite faults and/or fractures, which may occur in it. In this work, we present an ongoing injection experiment performed in a fault hosted in clay at the Mont Terri underground rock laboratory (NW Switzerland). The experiment aims to improve our understanding of the main physical and chemical mechanisms controlling (i) the migration of CO₂ through a fault damage zone, (ii) the interaction of the CO₂ with the neighboring intact rock, and (iii) the impact of the injection on the transmissivity in the fault. To this end, we inject CO₂-saturated saline water in the top of a 3 m thick fault in the Opalinus Clay, a clay formation that is a good analog of common caprock for CO₂ storage at depth. The mobility of the CO₂ within the fault is studied at the decameter scale by using a comprehensive monitoring system. Our experiment aims to close the knowledge gap between laboratory and reservoir scales. Therefore, an important aspect of the experiment is the decameter scale and the prolonged duration of observations over many months. We collect observations and data from a wide range of monitoring systems, such as a seismic network, pressure temperature and electrical conductivity sensors, fiber optics, extensometers, and an in situ mass spectrometer for dissolved gas monitoring. The observations are complemented by laboratory data on collected fluids and rock samples. Here we show the details of the experimental concept and installed instrumentation, as well as the first results of the preliminary characterization. An analysis of borehole logging allows for identifying potential hydraulic transmissive structures within the fault zone. A preliminary analysis of the injection tests helped estimate the transmissivity of such structures within the fault zone and the pressure required to mechanically open such features. The preliminary tests did not record any induced microseismic events. Active seismic tomography enabled sharp imaging the fault zone.

中文翻译：

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用于CO ₂封存的断层封闭和盖层完整性：原位注入实验

地质碳储藏的成功取决于对深层储藏地层中注入的二氧化碳（CO ₂）的永久遏制。CO ₂的安全保存的关键要素之一是覆盖层在储层之上的密封能力，尽管可能发生断层和/或断裂。在这项工作中，我们介绍了正在进行的注入实验，该实验是在Mont Terri地下岩石实验室（瑞士西北）的黏土断层中进行的。该实验旨在增进我们对控制（i）CO ₂通过断层破坏带的迁移，（ii）CO ₂相互作用的主要物理和化学机理的理解。（iii）注入对断层中透射率的影响。为此，我们在Opalinus粘土的3 m厚断层的顶部注入了充满CO _2的盐水，这种粘土的形成与普通盖岩在深层中储存CO ₂的良好相似。CO ₂的迁移率通过使用全面的监控系统，可以在十米级范围内研究故障内部。我们的实验旨在弥合实验室规模和储层规模之间的知识鸿沟。因此，实验的一个重要方面是十米刻度和长时间观察的持续时间。我们从各种监测系统收集观测和数据，例如地震网络，压力温度和电导率传感器，光纤，引伸计以及用于溶解气体监测的现场质谱仪。观察结果得到了有关收集的流体和岩石样品的实验室数据的补充。在这里，我们显示了实验概念和安装的仪器的详细信息，以及初步表征的初步结果。对钻孔测井的分析可以识别断层带内潜在的水力传输结构。对注入测试的初步分析有助于估算断层区域内此类结构的透射率以及机械打开此类特征所需的压力。初步测试未记录任何诱发的微地震事件。主动地震层析成像可以对断层带进行清晰成像。