Experimental Determination of CO₂ Diffusion Coefficient in a Brine-Saturated Core Simulating Reservoir Condition

CO₂ diffusion coefficient plays a crucial part in saline aquifers for the CO₂ storage and the safety of long-term sequestration. Therefore, it is particularly important to measure the diffusion coefficient accurately. As far as we know, there are currently no CO₂ brine diffusion data in real cores under reservoir temperature and pressure conditions. In this paper, a study on the CO₂ diffusion coefficient diffused in a brine-saturated Berea core along the radial direction was conducted at temperatures of 313.15 K to 373.15 K and pressures of 8 MPa to 30 MPa. On account of the experimental results, the effect of permeability, NaCl concentration, temperature and pressure on the CO₂ diffusivity is analyzed. The results in this study indicate that the diffusion coefficient increases with increasing permeability, pressure and temperature and decreases with increasing NaCl concentration. However, the relationship between pressure and the diffusion coefficient is not linear. As the pressure gradually increases, the effect of pressure will become weak. In addition, an empirical correlation of the relationship between temperature–pressure and the CO₂ diffusion coefficient could be obtained based on the experimental data. The data in this paper fill the blank on the study of the CO₂ diffusivity in brine under reservoir conditions, which has positive significance for the study of supercritical CO₂ diffusion in a brine-saturated core.