彭玺伊,王延永,李嵩,王晓光,崔国栋,何勇明
PENG Xiyi,WANG Yanyong,LI Song,WANG Xiaoguang,CUI Guodong,HE Yongming

• 1:成都理工大学能源学院
• 2:成都理工大学油气藏地质及开发工程全国重点实验室
• 3:天府永兴实验室
• 4:中国地质大学(武汉)工程学院

摘要(Abstract)：

【目的】CO_2咸水层封存是实现大规模温室气体减排的关键技术。对离岸浅部咸水层，海洋低温环境与上覆海水压力作用使其温度和压力条件相较于相同埋深陆上咸水层差异明显，地层内CO_2可能以液态形式存在。与超临界态相比，液态CO_2的密度、黏度及其在地层水中的溶解度更高，影响其运移和封存过程。现有研究以超临界CO_2为主，液态CO_2在咸水层中的运移和封存规律缺乏深入认识。【方法】考虑液态与超临界态CO_2特征，构建浮力与毛管力作用下CO_2运移与封存的数学模型。基于高精度两相渗流数值模拟，对比注气结束后液态与超临界态CO_2在咸水层中的运移特征和封存方式变化规律。【结果和结论】结果表明：与超临界态相比，浮力主导下液态CO_2垂向运移速率降低，波及体积减小。25 a后不同封存方式下液态CO_2的封存量要明显低于超临界态，咸水层的封存容量更难被充分利用。局部毛管力封存占比55%，残余气封存约为40%，溶解气封存占比5%，相态对不同封存方式贡献的影响较小。地温梯度的增大有利于强化液态CO_2的垂向运移，增加其波及体积，提高不同封存方式封存量及咸水层封存容量的利用效率。相同埋深条件下，超临界CO_2在陆上与离岸咸水层中运移特征和封存量呈现明显差异。离岸咸水层中超临界CO_2的垂向运移被抑制，降低了局部毛管力和残余气作用下CO_2封存量，不利于咸水层封存容量的有效利用。研究成果可为陆上和离岸咸水层CO_2高效封存提供一定指导。
[Objective] CO_2 storage in saline aquifers serves as a critical technology used to dramatically reduce greenhouse gas emissions. Owing to the low-temperature marine environment and the pressure from overlying seawater, shallow offshore saline aquifers exhibit significantly different temperature and pressure conditions compared to onshore saline aquifers at equivalent burial depths, allowing CO_2 to occur in a liquid state. Compared to supercritical CO_2, liquid CO_2 features higher density, viscosity, and solubility in formation water, which affect the CO_2 migration and storage processes. Previous studies focus primarily on supercritical CO_2, lacking a deep understanding of the migration and storage patterns of liquid CO_2 in saline aquifers. [Methods] Considering the distinct characteristics of liquid and supercritical CO_2, this study constructed a mathematical model for CO_2 migration and storage under the action of buoyancy and capillary pressure. Using the high-precision numerical simulations of two-phase seepage, this study compared the laws of changes in the migration characteristics and storage forms of liquid and supercritical CO_2 in saline aquifers after gas injection. [Results and Conclusions] The results indicate that compared to supercritical CO_2, liquid CO_2 manifested reduced vertical migration rates and swept volumes under buoyancy-dominated conditions. After 25 a, the storage amounts of liquid CO_2 in different storage forms were significantly lower than those of supercritical CO_2, making it more difficult to fully leverage the storage capacity of saline aquifers. Among the different CO_2 storage forms, local capillary trapping, residual gas trapping, and solubility trapping represent 55%, 40%, and 5%, respectively, with the CO_2 phase states posing minor impacts on the storage forms. An increase in geothermal gradient enhanced the vertical migration and swept volume of liquid CO_2, the CO_2 storage amounts of different storage forms, and the utilization efficiency of the storage capacity of saline aquifers. At the same burial depths, supercritical CO_2 displayed significantly different migration characteristics and storage amounts in onshore and offshore saline aquifers. The inhibited vertical migration of supercritical CO_2 in offshore saline aquifers reduced the CO_2 storage amounts of local capillary trapping and residual gas trapping, hampering the effective utilization of the storage capacity of saline aquifers. The results of this study can serve as a guide for efficient CO_2 storage in onshore and offshore saline aquifers.

关键词(KeyWords)： 咸水层;CO_2地质封存;相态;浮力;毛管力;封存方式
saline aquifer;CO_2 geological storage;phase state;buoyancy;capillary force;storage form

Abstract:

Keywords:

基金项目(Foundation): 四川省科技计划项目(2022YFSY0008);; 国家自然科学基金项目(52404021)

作者(Author): 彭玺伊,王延永,李嵩,王晓光,崔国栋,何勇明
PENG Xiyi,WANG Yanyong,LI Song,WANG Xiaoguang,CUI Guodong,HE Yongming

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