A Study on Long-term Stability of CO2 Geological Sequestration

二氧化碳排放量的增加被认为是全球变暖的一个因素，并研究了各种封存技术。然而，二氧化碳的长期行为还没有得到很好的理解。注入地下含水层的二氧化碳稳定为气相、液相或固相。溶解在液相中的二氧化碳通过对流弥散现象在含水层中扩散。有必要评估孔隙级非均质性对流动特性的影响。在本研究中，采用砂岩、碳酸盐岩和一包玻璃珠进行了实验。采用对流-弥散（CDE）模型和Coats-Smith模型作为流动模型，并与实验结果进行了匹配。ODE在一组玻璃珠和砂岩的应用取得了成功。此外，还证实了无论何种样品，色散系数都与流速成正比。另一方面，CDE在白云岩中的应用并不成功。这主要是由于次生孔隙和孔隙层的非均质性所致。采用反映非均质性的Coats-Smith模型，得到了较好的匹配结果。样品中存在大量的滞止部分，表明具有孔隙级非均质性的岩石比不具有这种非均质性的岩石和玻璃球具有更大的色散系数。当使用用ODE模拟色散的流动模拟器时，使用Coats-Smith模型得到的色散系数可能会导致错误的预测。为获得可接受的预测结果，为。有必要设置一个大于实际的表观系数

The increase in discharge of carbon dioxide is considered as a factor of global warming, and various sequestration technologies are studied. However, the long-term behavior of carbon dioxide is not well understood. The carbon dioxide injected into underground aquifer is stabilized as a gaseous phase, a liquid phase, or a solid phase. The carbon dioxide dissolved in the liquid phase spreads by convection-dispersion phenomena in the aquifer. It is necessary to evaluate the influence of pore-level heterogeneity on the flow behavior. In this research, the experiment using sandstone, carbonate rock, and a pack of glass bead was conducted. A convection-dispersion (CDE) model and the Coats-Smith model were adopted as a flow model, and matching with an experiment result was performed. Application of ODE was successful for a pack of glass bead and sandstone. Moreover, it has been confirmed that the dispersion coefficient was proportional to the flow velocity regardless of the kind of sample. On the other hand, application of CDE was not successful for the dolomite. This is because the secondary pore and the pore-level heterogeneity. When the Coats-Smith model reflecting the heterogeneity was applied, the good matching result was obtained. A large amount of stagnation portion exists in the sample, and it turned out that the rock which has the pore-level heterogeneity may have a large dispersion coefficient compared with the rock and the glass bead without such heterogeneity. When using flow simulators which models dispersion by ODE, using the dispersion coefficient obtained from the Coats-Smith model may result in erroneous predictions. To obtain acceptable-prediction results, it is. necessary to set up an apparent coefficient that is larger than the actual