Molecular insight into replacement dynamics of CO2 enhanced oil recovery in nanopores

Nanopores are widely found in unconventional reservoirs, and the effect of nanoconfinement on CO2 enhanced oil recovery is still not fully understood. In this work, we have studied the kinetics of alkane replacement using CO2 in micropores (<2 nm) using molecular dynamics simulations. We found that the microstructures (number and density of adsorption layers) of n-decane in micropores changes dramatically with the pore size, leading to oscillations in the density and diffusivity of n-decane in the pores. A diffusion model was proposed to describe the replacement process of CO2 and analyze the different replacement mechanisms under different pore sizes. The structure change pattern and replacement efficiency were examined to show the superiority of microporosity in mining. This work paves a new way to explore the replacement mechanism in micropores, demonstrating the importance of micropores in CO2 enhanced oil recovery.