Flow regime transition of multicomponent oil in shale nanopores

Understanding the shale oil flow mechanism in nanopores is crucial for optimizing development strategies and enhancing recovery in shale oil reservoirs. Despite the widespread use of molecular dynamics simulations in studying shale oil flow, oversimplified shale oil and shale nanopore models compromise result reliability, and a definitive shale oil flow regime has yet to be established. This study, employing validated molecular models, investigated 26-component oil flow in authentic shale kerogen and quartz nanopores. For the first time, we elucidated the nonlinear flux increase due to flow regime transition with pressure gradient. At low pressure gradients, shale oil flux gradually increased with a parabolic velocity profile. With the increasing pressure gradient, the velocity profile shifted from parabolic to piston-like, especially in quartz nanopores, indicating a positive slip velocity. Consequently, the shale oil flux increased significantly. At high pressure gradients, the growth of shale oil flux decelerated while maintaining a piston-like velocity profile. Through analysis of density distribution and oil-wall interactions, we revealed that oil desorption and redistribution triggered the flow regime transition. The flow regime transition occurred with the widening of quartz nanopores. Increased nanopore width and temperature notably enhanced shale oil flow. This study underscored the importance of accounting for shale oil's multicomponent properties and roughness and composition of shale nanopores. It determined shale oil flow regimes under various conditions, advancing our comprehension of shale oil flow mechanisms in realistic settings and furnishing a theoretical foundation for enhancing shale oil recovery.