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.