Abstract

CO2 geological storage is a promising method to dispose excess CO2 in the atmosphere, and the existence of brine in deep saline aquifer and below oil reservoir may lead to salt precipitation in pore space for dry-out formation. Water diffusion coefficient is helpful to evaluate salt precipitation. However, limited previous data cant satisfy the need of CO2 geological storage. Raman quantitative spectroscopy is used to observe water diffusion in CO2 in a high-pressure capillary cell and corresponding diffusion coefficients are obtained at 10-50 MPa and 353.15-433.15 K. Diffusion coefficient is temperature and pressure dependent, and also increases linearly with the reciprocal of CO2 density. Free volume theory and PC-SAFT EOS are utilized to establish a thermodynamic model for water diffusion in CO2, and it predicts diffusion coefficient accurately at 10-50 MPa and 353.15-433.15 K. Besides, diffusion coefficient is used to evaluate when salt precipitation occurs and salt precipitation process is observed in a one-dimensional capillary tube and a two-dimensional micromodel respectively.