Associated gas recovery and CO2 displacement mechanisms in nanopores are critical for optimizing tight oil reservoir development. To investigate these processes in the Hesui area of the Ordos Basin, molecular dynamics simulations utilizing the COMPASSIII force field and NVT ensemble were conducted on experimental associated gas mixtures within 5 nm polar quartz and non-polar graphite slit-pores. The study evaluated free diffusion, adsorption energies, and displacement behaviors. Results reveal that pore walls generally suppress gas diffusion compared to free states, although CO2 exhibits anomalously high diffusion on graphite due to surface slip. Additionally, non-polar graphite demonstrates stronger alkane adsorption than quartz, forming stable, low-energy layered structures. During CO2 injection, displacement on quartz yields an incomplete layered structure governed by Poiseuille flow. Conversely, graphite facilitates displacement primarily in the pore center, characterized by low-friction slip flow and superior transport efficiency. In conclusion, pore wall polarity and chemical composition fundamentally govern associated gas migration and CO2 displacement efficiency. These microscopic insights provide theoretical guidance for enhancing resource utilization and CO2 displacement strategies in tight oil reservoirs.
Jia et al. (Mon,) studied this question.