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盖层密封性能对CO_2地质封存工程的容量、经济性、安全性具有重要影响。盖层岩石具有明显的层状非均质特点,而这种层状非均质特点直接影响CO_2在盖层中的迁移与泄漏过程,从而影响盖层的密封性能。现有研究考虑了各向同性的非均质性对盖层密封性能的影响,但并未针对层状非均质性盖层展开相应的研究。建立了考虑孔隙度、渗透率和毛管压力参数变化关系的均质、非层状非均质和层状非均质3种盖层地质模型,并采用TOUGH2对统一边界条件的不同地质模型开展了数值模拟对比研究,分析了CO_2进入盖层、盖层内迁移和穿透盖层而形成缓慢泄漏的全过程。模拟结果表明:3种模型中,自由态CO_2饱和度分布与孔隙度、渗透率的分布基本一致;与均值模型相比,非层状非均质性会加速CO_2在盖层中的迁移,而层状非均质性将会阻碍CO_2在盖层中的迁移,增加穿透时间;与均质模型和非层状非均质模型相比,层状非均质模型将会大大降低CO_2的穿透盖层以后的泄漏速率和泄漏总量。针对建模和数值模拟过程中遇到的问题,提出了盖层地质建模过程中的一些局限性。其结果为更加客观和定量地评价CO_2在盖层内迁移规律及泄漏量奠定了一定的基础。
Cap sealing performance of CO_2 geological storage project capacity, economy, safety has an important impact. The cap rocks have obvious stratigraphic heterogeneity, and this layer heterogeneity has a direct impact on the migration and leakage of CO_2 in the caprocks, which will affect the caprock sealing performance. The existing research considers the influence of isotropic heterogeneity on the sealing performance of the capping layer, but does not start the corresponding research on the layered heterogeneous capping layer. Three geological models of homogenization, non-laminar heterogeneity and stratified heterogeneity are established considering the relationship between porosity, permeability and capillary pressure. The different geological models with uniform boundary conditions are developed by TOUGH2 Numerical simulation comparative study, the CO_2 into the cap layer, cap layer migration and penetration through the cap layer to form a slow leak of the entire process. The simulation results show that in the three models, the distribution of CO_2 saturation in free state is basically consistent with the distribution of porosity and permeability. Compared with the mean model, non-layered heterogeneity accelerates the migration of CO_2 in the cap rock Lamellar heterogeneity will hinder the migration of CO 2 in the caprock and increase the breakthrough time. Compared with the homogeneous model and the non-layered heterogeneous model, the layered heterogeneous model will greatly reduce the CO 2 penetration Leakage rate and total leakage after the overburden. In view of the problems encountered in modeling and numerical simulation, some limitations in the process of geological modeling of overburden are proposed. The results laid a solid foundation for more objective and quantitative evaluation of CO_2 migration and leakage in the caprock.