Mechanism and Models of Nano-Confined Slip Flow of Shale Oil

The flow of shale oil in nano-scale rock pores follows the slip flow regime, in which the flow velocity at the nanopore walls is not zero. The nano-scale effect of the boundary layer renders the slip flow effect in the nanopores non-negligible. In this study, the slip flow mechanism of shale oil in nanopores was reviewed. The nano-scale effect of the boundary layer renders the slip flow effect in the nanopores non-negligible. The slip length and flow enhancement factor are the primary parameters used to evaluate the slip effect. The main factors influencing the slip effect were then analyzed, including the fluid properties, nanopore properties, pressure gradient, and temperature. Additionally, three slip flow models for shale oil in circular, elliptical and slit nanopores were reviewed. Moreover, a modification method for the shape factor is introduced to evaluate the slip effect of irregular nanopores. The general conclusions regarding the mechanism and models of slip flow in shale oil are summarized as follows: (1) Slip flow of shale oil occurs predominantly in nanopores due to scale effects and stronger internal interaction forces among alkane molecules. (2) The influence of slip flow is more pronounced in organic nanopores than in inorganic nanopores. (3) Significant slip flow effects are observed with larger slip lengths and flow enhancement factors. (4) Our analytical models indicated that slip flow effects are more pronounced with smaller hydraulic diameters. (5) The effects of slip flow are more pronounced in nanopores with irregular geometric shapes. Lastly, recommendations for future research are proposed.