Faculty of Engineering, China University of Geosciences
College of Energy Resources, Chengdu University of Technology

实际咸水层呈垂向多层分布，物性差异大，毛管力非均质性严重。非纯CO2气体封存过程中，毛管力不仅会圈闭CO2，更会圈闭伴随的杂质气体，影响CO2运移和封存。但是，垂向多层系下毛管力的圈闭机制还不清楚，其对非纯CO2气体封存效率的影响亟待分析。为此结合随机统计地质建模和非纯CO2−盐水两相渗流模型，建立了垂向多层系咸水层非纯CO2封存运移模型；研究了毛管力作用下CO2和杂质气体的运移过程及其羽流发育规律，并对非纯CO2气体垂向运移速率和毛管力圈闭能力进行了量化计算；最后通过敏感性分析，阐明了毛管力大小、非均质程度、杂质体积分数等因素对非纯CO2气体封存效率的影响。研究结果表明，非均质毛管力可有效圈闭非纯CO2气体，增加非纯CO2气体在横向上的波及体积；随着毛管力大小和非均质程度增加，毛管力圈闭量升高，毛管力封存系数增大，但CO2垂向运移速率降幅明显，与杂质气体垂向运移速率的差异幅度增加。毛管力自上而下递减时，底部毛管力圈闭减少，更多的非纯CO2气体将运移到地层上部的各个区域，使得非纯CO2气体毛管力封存系数增加，非纯CO2气体残余封存系数减少，CO2垂向运移速率增大，与杂质气体垂向运移速率的差异幅度减小；随着杂质气体体积分数增加，非纯CO2气体浮力增加，垂向运移速率增大，更多非纯CO2气体运移到地层顶部，非纯CO2气体毛管力封存系数降低，残余封存系数增加。因此为保证封存安全性，应尽可能选择含杂质少的非纯CO2气体注入毛管力大、非均质性强以及垂向毛管力自上而下先递增后递减的咸水层。

The actual saline aquifers is vertically distributed in multiple layers, with large differences in physical properties and serious heterogeneity of capillary pressure. During the sequestration of impure CO2, the capillary pressure will not only trap CO2 but also trap the accompanying impurity gas, affecting CO2 migration and sequestration. However, the entrapment of local capillary under the vertical multi-layer system is still unclear, and its impact on the sequestration efficiency of impure CO2 needs to be analyzed urgently. For this reason, stochastic statistical geological modeling and impure CO2-brine two-phase seepage model are combined to establish a vertical multi-layer impure CO2 sequestration and migration model in saline aquifers. Under the action of capillary pressure, the migration process and its plume development law are studied and the vertical migration rate of impure CO2 and the capillary pressure trapping ability are calculated quantitatively. Finally, through the sensitivity analysis, the capillary pressure, the influence of capillary pressure, heterogeneity, and impurity volume fraction on CO2 sequestration efficiency is clarified. The research results show that heterogeneous capillary pressure can effectively trap impure CO2 and increase the swept volume of impure CO2 in the lateral direction. With the increase of capillary pressure and its heterogeneity, local capillary trap volume and local capillary sequestration coefficient increase. However, the vertical migration rate of CO2 decreases significantly, and the difference between the vertical migration rate of impurity gas increases. When the capillary pressure decreases from top to bottom, the local capillary entrapment at the bottom decreases, and more impure CO2 will migrate to various areas in the upper part of the formation, which makes the local capillary sequestration coefficient of impure CO2 increase, and the residual sequestration coefficient of impure CO2 decrease. What’s more, it makes the vertical migration rate of CO2 increase and the difference between the vertical migration rate of impurity gas and impurity gas decrease. As the volume fraction of impurity gas increases, the buoyancy of impure CO2 and the vertical migration rate of impure CO2 increase. More impure CO2 migrates to the top of the formation, which makes the local capillary sequestration coefficient of impure CO2 decrease, while residual sequestration coefficient increases. Therefore, to ensure the safety of storage, impure CO2 containing few impurities should be selected as much as possible to inject into the saline aquifers with large capillary pressure, strong heterogeneity, and vertical capillary pressure increasing first and then decreasing from top to bottom.

国家自然科学基金资助项目(42202349,42227805)；湖北省自然科学基金资助项目(2021CFB189)

崔国栋，胡哲，宁伏龙，等. 咸水层毛管力圈闭机制及对非纯CO2封存效率的影响[J]. 煤炭学报，2023，48(7)：2791−2801.

CUI Guodong，HU Zhe，NING Fulong，et al. Local capillary entrapment and its effect on sequestration efficiencies during impure CO2 injection into saline aquifers[J]. Journal of China Coal Society，2023，48(7)：2791−2801.