Research on the Characteristics and Mechanisms of Supercritical CO2 Displacement of Shale Oil Under Nanoscale Confinement

Abstract

Shale reservoirs, characterized by compact pores, poor physical properties, and high organic matter content, exhibit significant differences in microscopic flow behavior compared to conventional oil reservoirs. These distinctions complicate the accurate assessment of shale oil reserves and the selection of optimal exploration and development strategies. Understanding the mechanisms and factors influencing microscopic flow in shale oil is crucial for both theoretical and practical aspects of shale oil exploration and development. In this study, molecular dynamics simulations employing the Grand Canonical Monte Carlo method were used to develop a microscale molecular dynamics model for n-octane (C₈H₁₈) adsorption on various adsorbents. Adsorption energies for organic materials (kerogen), brittle minerals (quartz, albite), carbonate minerals (calcite), and clay minerals (illite, kaolinite, montmorillonite) were calculated to evaluate the adsorption strength of shale oil and CO₂ on these adsorbents. Furthermore, a nonequilibrium molecular dynamics (NEMD) approach was utilized to model the CO₂ displacement of shale oil in different slit pores, exploring the flow characteristics and displacement mechanisms of supercritical CO₂ under nanoscale confinement. This investigation also considered the effects of CO₂ density, slit pore surface properties, and driving force magnitudes, providing essential theoretical and technical insights for assessing shale oil reserves and refining exploration and development strategies.