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.