Numerical modeling of CO_2 diffusion into water-oil liquid system using moving mesh technique

摘要

A new diffusion model is developed to study the mass diffusion of CO2 in the water-oil liquid system. The diffusion stages are divided by the position of diffused CO2 front in the liquid system. The 1st and 2nd diffusion stages are performed to characterize the CO2 diffusion in individual oil phase and in water-oil liquid system, respectively. The Peng-Robinson equation of state combined with the diffusion model of two stages are developed to describe the diffusion process of CO2 in the water-oil liquid system. The developed model is validated by matching the pressure changes results of model calculation with an experimental acquisition. Besides, a moving mesh technique is applied to determine the oil swelling effect caused by the CO2 diffusion. The results indicate that both CO2 concentration profiles and oil swelling effect exhibit distinct characteristics at different stages. The CO2 distributes only in the oil phase at the 1st diffusion stage but presents simultaneously in both water and oil phases at the 2nd diffusion stage. The oil swelling factors are 0.90% and 10.84% at the end of the 1st (t = 12.8 h) and 2nd (t = 512.8 h) diffusion stages, respectively.