Understanding the hydro-mechanical response of a reservoir and its surrounding rocks to the CO pressure build-up during CO injection process is a key challenge in the safe implementation of CO capture and storage (CCS) technologies. These responses are expected to depend on the type of formation properties, such as hardness of the reservoir rocks. This study investigates permeability behavior of various soft sedimentary rocks that are commonly in candidate reservoirs, considering geological CO storage in Japan during shear-fracturing processes. Both the pre- and post-failure regimes were examined using direct shear-fracturing tests with simultaneous measurements of permeability. Our results demonstrated that the permeability of the tested specimens varied widely during shear-fracturing, depending on their failure mechanisms (i.e., brittle or ductile). The magnitude of the change in permeability during shear-fracturing was consistent with the geometry of the fracture patterns formed in the rock matrix after the experiment, indicating that, during slipping, the permeability behavior may be related to the fractured plane roughness. We found that the brittleness index was linearly correlated with the maximum change in permeability in most samples; this correlation provides insight into the hydro-mechanical responses of soft sedimentary rocks for assessments of the CO seal integrity in caprocks and compartments of reservoir rocks and should be considered when conducting numerical simulations of CO sequestration sites.

中文翻译：

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CO2注入过程中软岩流体力学响应的实验研究——裂缝粗糙度和脆性指数对渗透行为演化的影响


了解二氧化碳注入过程中储层及其周围岩石对二氧化碳压力累积的流体力学响应是安全实施二氧化碳捕集和封存（CCS）技术的关键挑战。这些响应预计取决于地层性质的类型，例如储层岩石的硬度。本研究研究了候选储层中常见的各种软沉积岩的渗透行为，考虑了日本在剪切压裂过程中的地质二氧化碳储存。使用直接剪切断裂试验并同时测量渗透率来检查故障前和故障后状态。我们的结果表明，测试样本的渗透率在剪切断裂过程中变化很大，具体取决于其失效机制（即脆性或延性）。剪切压裂过程中渗透率的变化幅度与实验后岩石基质中形成的裂缝模式的几何形状一致，表明在滑移过程中，渗透率行为可能与裂缝面粗糙度有关。我们发现，在大多数样品中，脆性指数与渗透率的最大变化呈线性相关；这种相关性可以深入了解软沉积岩的流体力学响应，以评估盖层和储层岩石隔室中二氧化碳封闭的完整性，并且在对二氧化碳封存地点进行数值模拟时应考虑到这一点。