Abstract CO2 sequestration in saline aquifers is considered to be a promising method for climate mitigation. Studies of the subsurface flow mechanisms of CO2–brine are important for evaluation of sequestration potential and security. However, this process is complicated by the intrinsic heterogeneity of reservoir rocks. The main objective of this study was to identify CO2 distribution and saturation related to changing injection conditions, and to comprehensively compare the characteristics of different drainage processes, under small scale heterogeneous condition. An X-ray computed tomography machine and a micromodel were introduced to investigate the CO2/brine drainage process from pore to core scale in a wide range of injection rates at static and transient states, respectively. Four types of drainage experiments were conducted. Horizontal and vertical (upward) flow directions in a micromodel setup at ambient conditions and vertical (upward and downward) flow directions in a core-flood setup at in-situ conditions. Based on experimental results, it is found that, a higher injection rate gives rise to a higher displacement efficiency but a lower sweep efficiency. The stability of CO2 displacing front become weak with drainage development. The difference in pore structure leads to different CO2 saturation variation with CO2 injection rates change. Even the sand pack is almost homogenous at core scale, the impact of heterogeneous porosity is enhanced with increasing flow rates in upward drainage, while it weakens in downward drainage.

中文翻译：

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CO2在无序孔径水饱和多孔介质中的渗透研究

摘要 咸水层中的二氧化碳封存被认为是缓解气候变化的一种有前途的方法。研究 CO2-盐水的地下流动机制对于评估封存潜力和安全性很重要。然而，这一过程由于储集岩固有的非均质性而变得复杂。本研究的主要目的是确定与注入条件变化相关的 CO2 分布和饱和度，并在小规模非均质条件下综合比较不同排水过程的特征。引入了 X 射线计算机断层扫描仪和微模型，分别在静态和瞬态状态下，在各种注入速率下研究从孔隙到岩心尺度的 CO2/盐水排放过程。进行了四种类型的排水实验。环境条件下微模型设置中的水平和垂直（向上）流向，以及原位条件下岩心洪水设置中的垂直（向上和向下）流向。根据实验结果发现，较高的注入速度会产生较高的驱替效率，但会导致波及效率较低。CO2 驱替锋面的稳定性随着排水系统的发展而减弱。孔隙结构的差异导致 CO2 饱和度随 CO2 注入速率的变化而变化。即使砂岩在岩心尺度上几乎是均质的，但不均匀孔隙度的影响随着向上排水流速的增加而增强，而在向下排水时则减弱。