封存CO_2裹挟可挥发性污染物的迁移模型分析

Analysis of migration model for volatile contaminants induced by CO_2 geological storage

为了研究封存CO2注入过程可挥发性污染物的释放和迁移特性,本文建立了CO2-水-残余油多相流驱替过程中的污染物迁移模型。采用数学模拟方法分析了多相驱替过程和污染物迁移过程,并研究了相间传质特性、初始油相分布和CO2注入速率等对污染物迁移过程的影响。研究表明:CO2驱替过程将促使可挥发污染物进入CO2相并随之在地层中迁移,逐渐形成相间传质区域。相间传质区域的演化反映了污染物释放和CO2裹挟污染物迁移的特性。可挥发污染物的传质系数越大,相间传质区域越窄,油相饱和度衰减越快;油相初始饱和度较大时,其饱和度衰减相对缓慢,对应的相间传质区域也较窄。当CO2注入速率增大时,相间传质区域增大,油相饱和度衰减变快。本文模型可用于不同地质储层环境下封存CO2时可挥发性污染物的迁移特性分析,并用于封存CO2的风险分析与评价。

In order to investigate characteristics of volatile contaminant release and migration during CO2 geological sequestration, a contaminant migration model with multiphase displacement process in a CO2-aqueous phase-residual oil phase system was proposed. Numerical simulations were performed to figure out the multiphase displacement and the contaminant migration, and further to explore the effects of interphase mass transfer, initial profiles of the residual oil and injection rates on the volatile contaminant migration. The results indicate that the volatile contaminant enters into the supercritical CO2 phase due to the multiphase displacement process, and migrates with the mobile phase in the subsurface formation. An interphase mass transfer region （IMTR） gradually forms. The evolution of IMTR directly reflects the release characteristics of contaminant and migration behaviors of CO2 coerced with contaminant. A larger interphase mass transfer coefficient results in a narrower IMTR and a faster decay rate of the oil phase. When the initial saturation of the oil phase is larger, the IMTR becomes much narrower and the oil phase decays much slower. With increasing CO2 injection rate, IMTR increases and the oil phase decays rapidly. The proposed model and the results intuitively describe the migration characteristics of the volatile contaminants in a variety of geological reservoirs during CO2 geological sequestration. The proposed model can also be used for the risk analysis and evaluations of CO2 storage.