A general method for determining the diffusivity coefficient of supercritical CO₂ in cores saturated with oil is presented in this paper. Theoretically, a mathematical model including Fick’s diffusion equation and Peng–Robinson Equation of State (PR EOS) is proposed to evaluate the mass transfer of CO₂ in the cores with different permeabilities. Experimentally, the pressure-decay method is employed by monitoring the CO₂ pressure in the diffusion cell during diffusion experiments. The CO₂ diffusion coefficients in the cores with different permeabilities are determined when the discrepancy of the calculated and measured pressure-decay curves has been minimized. The diffusion coefficient of supercritical CO₂ increases gradually with rising permeability at the range of 0.1–10 mD, and then it reaches a plateau at the permeability range of 10–300 mD. The impact of the permeability on the CO₂ diffusion coefficient is attributed to the pore radius and pore structure of the cores. The Pore radius of the core whose permeability is less than 10 mD is less than 1 μm, and pore walls restrict CO₂ mass transfer under such condition, which accounts for the relative low diffusion coefficient. When the permeability exceeds 10 mD, the pore radius is larger than 1 μm, and the influence of the solid boundary is negligible. Moreover, the textural coefficients of cores decrease with the permeability, which shows that the less tortuous pore structure facilitates the mass transfer process. Diffusive tortuosities for the cores with different permeabilities are determined by using the CO₂ diffusion coefficients in porous media and bulk phase, which show the same trend with the pore radius distribution.

提出了一种确定油饱和的岩心中超临界CO ₂扩散系数的通用方法。从理论上讲，提出了一个包含Fick扩散方程和Peng-Robinson状态方程（PR EOS）的数学模型，以评估不同渗透率岩心中CO ₂的传质。在实验中，通过在扩散实验过程中监视扩散池中的CO ₂压力来采用压力衰减方法。当计算和测量的压力衰减曲线的差异最小化时，可以确定具有不同渗透率的岩心中的CO ₂扩散系数。超临界CO ₂的扩散系数随着渗透率在0.1–10 mD范围内的增加而逐渐增加，然后在10–300 mD的渗透率范围内达到平稳。渗透率对CO ₂扩散系数的影响归因于芯的孔半径和孔结构。渗透率小于10 mD的岩心的孔半径小于1μm，并且孔壁限制了CO ₂在这种条件下传质，这是相对较低的扩散系数。当渗透率超过10mD时，孔半径大于1μm，并且固体边界的影响可以忽略。此外，岩心的结构系数随着渗透率的降低而降低，这表明较少弯曲的孔结构促进了传质过程。利用渗透介质和本体相中的CO ₂扩散系数，确定了不同渗透率岩心的扩散曲折度，与孔隙半径分布趋势相同。