关键词: CO₂, 封存, 多相流, 驱替过程, 相间传质, 污染物迁移

Abstract:

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.

Key words: CO₂, sequestration, multiphase flow, displacement process, interphase mass transfer, contaminant migration