Effects of Pore Structures on Seepage and Dispersion Characteristics during CO2 Miscible Displacements in Unconsolidated Cores

In the challenge of decarbonization, an economical option for carbon capture, utilization, and storage is carbon dioxide enhanced oil recovery (CO2-EOR) and sequestration in depleted oil reservoirs. During the CO2-EOR processes, pore structures have significant effects on miscible flow performance. The permeability and heterogeneity are investigated by magnetic resonance imaging for seepage characteristics in this study. Furthermore, the dispersion coefficient and Peclet number are calculated by the error function for dispersion characteristics. The whole displacements are relatively stable with piston-like fronts in homogeneous cores while quite unstable with fingering fronts in heterogeneous cores. The results exhibited that the mixing zone length, mixing zone velocity, recovery factor, dispersion coefficient, and Peclet number are significantly affected by heterogeneity but less affected by permeability in the miscible displacement process. This indicates that the seepage and dispersion are more affected by the heterogeneity rather than the permeability. Heterogeneity is a more important parameter than permeability. To further investigate the micromechanism of supercritical CO2 miscible flows, the Lattice-Boltzmann method (LBM) is also used for local pore-space simulation, and the results showed that the fronts in local space are stable. The oil saturation results of the LBM simulation and BZ-04 experiment are closed at the A-B stage before the breakthrough time, and LBM is a good method for dealing with the microflow in miscible displacement. Therefore, more insight should be focused on heterogeneity rather than permeability. It is important to determine an effective parameter to represent heterogeneity in the future. Our study could support the application of oil recovery engineering.

Automated summary

This study investigates the permeability and heterogeneity in CO2-EOR processes using magnetic resonance imaging, revealing that heterogeneity has a significant impact on parameters like mixing zone length and velocity during miscible displacement, indicating that heterogeneity is more important than permeability in determining flow characteristics. The Lattice-Boltzmann method is also employed for local pore-space simulation, showing stable fronts in local space and suggesting that more attention should be focused on heterogeneity rather than permeability for future research.