Taylor Dispersion in Nanopores during Miscible CO2 Flooding: Molecular Dynamics Study

The miscible process between carbon dioxide (CO2) and oil in nanopore multiphase flow is essential for CO2-enhanced oil recovery (CO2-EOR) techniques, especially in low permeability oil reservoirs. The interplay between diffusion and convection dominates the miscible process in CO2-EOR. The Taylor dispersion model supposes that the shear flow smears the concentration distribution in the flow direction, thus enhancing the diffusion and convection in the capillary tube. However, the nanoscale applicability of this assumption is unclear. This work simulated the multiphase flows of CO2 and dodecane in nanopores at different flow velocities by using molecular dynamics (MD) simulations to investigate the process. Mass fraction profiles along the flow direction are overestimated using the Taylor dispersion model. Fluid velocity profiles from the MD results confirm the presence of the slippage phenomenon. A comparison between miscible flow and single-phase flow shows that the slip length of miscible flow might be the average of two single-phase flows of a specific component. A modified Taylor dispersion model considering slip boundary condition is obtained using the characteristic flow velocities modified by the slip length. The modified model-produced predictions correlated with the MD results and thus can predict the miscible process of nanoscale multiphase flow in CO2-EOR techniques.