Investigating the flow behaviors of multi-component oil in shale nanopores via MD simulations

Introduction Shale reservoirs contain a substantial number of nanopores. When the pore size is at the nanoscale, the confinement effect exerts a significant influence on shale oil flow within the pores. The flow mechanisms of shale oil in nanopores remain inadequately understood. Methods In this paper, molecular dynamics simulations were employed to investigate the flow behavior of multi-component shale oil in illite pores and to analyze the effects of pore size, temperature, and pressure on the flow characteristics. Results The results demonstrate that an increase in pore size intensifies the boundary slip phenomenon, thereby enhancing the flow velocity of shale oil within the pores. Elevated temperature reduces bulk viscosity and amplifies slip effects, consequently increasing the flow velocity in the pores. In contrast, increased pressure leads to a thicker adsorption layer, a reduced effective flow space, suppressed slip effects, and increased bulk viscosity, ultimately resulting in decreased shale oil flow velocity in nanopores. Discussion By accounting for the influences of the adsorption layer and slip effects, a modified equation that aligns with the simulation results was developed for describing shale oil flow in nanopores. This equation enables the prediction of flow velocities under different pore sizes and quantifies the impact of the confinement effect on flow rates. The findings provide theoretical support for the prediction of key seepage parameters of shale oil reservoirs.