Molecular Dynamics Simulation of Diffusion of Shale Oils in Montmorillonite

Shale oil is an important unconventional resource gathered in shales with nanoscale pores. In this work molecular dynamics simulations were performed to investigate the diffusion of shale oil in the clay-rich shale. The montmorillonite model was used to represent the clay-rich shale, and octane was used as a shale oil model. Results show that the diffusion coefficient of shale oils is extremely small in the basal spacing of 2.8 nm, and with the increase of basal spacing, the diffusion coefficient increases by several orders of magnitude. This observation indicates that once the shale oils flow from microscopic pores into the mesoscopic pores, it would be accompanied by the decrease of oil density and extreme increase of diffusion coefficient, which is very beneficial for exploitation of shale oils. However, it is still difficult to exploit the oil molecules adsorbed in the microscopic pore. Besides, by exploring the effect of chain length of the oil molecule on the diffusion, we found that the shorter chain oils are beneficial for exploitation. It is expected that these simulation results provide useful reference and important fundamentality for the investigation of shale oils.