Experimental study of the supercritical CO₂ diffusion coefficient in porous media under reservoir conditions

Reliable measurement of the CO₂ diffusion coefficient in consolidated oil-saturated porous media is critical for the design and performance of CO₂-enhanced oil recovery (EOR) and carbon capture and storage (CCS) projects. A thorough experimental investigation of the supercritical CO₂ diffusion in n-decane-saturated Berea cores with permeabilities of 50 and 100 mD was conducted in this study at elevated pressure (10-25 MPa) and temperature (333.15-373.15 K), which simulated actual reservoir conditions. The supercritical CO₂ diffusion coefficients in the Berea cores were calculated by a model appropriate for diffusion in porous media based on Fick's Law. The results show that the supercritical CO₂ diffusion coefficient increases as the pressure, temperature and permeability increase. The supercritical CO₂ diffusion coefficient first increases slowly at 10 MPa and then grows significantly with increasing pressure. The impact of the pressure decreases at elevated temperature. The effect of permeability remains steady despite the temperature change during the experiments. The effect of gas state and porous media on the supercritical CO₂ diffusion coefficient was further discussed by comparing the results of this study with previous study. Based on the experimental results, an empirical correlation for supercritical CO₂ diffusion coefficient in n-decane-saturated porous media was developed. The experimental results contribute to the study of supercritical CO₂ diffusion in compact porous media.