The transport behaviors of oil in nanopores and nanoporous media of shale

Abstract

Shale, known as the “tight” rock with abundant nanopores, exhibits extremely low permeability on the order of micro/nanodarcy. The classic Darcy law, being widely and successfully used in conventional porous media, becomes insufficient for the shale. In this work, on the basis of molecular dynamics (MD) simulations data available in the literature, a model for oil transport through a single nanopore is established by considering the boundary slip and the varying viscosity of the confined oil. Then, the established model for the single nanopore is integrated into the generalized lattice Boltzmann method (GLBM) to mimic the oil transport in the shale with nanopore networks, successfully scaled up to the nanoporous media. The results show that, to accurately predict the oil transport properties in inorganic and organic nanopores, the viscosity correction for the confined oil transport in the nanopores is necessary. The oil transport capability in organic nanopores is greatly enhanced compared with that predicted by the no-slip Poiseuille equation, significantly enhancing the flow capability in the scale of nanoporous media, while the small slip length in the inorganic matter (IOM) has neglected effect. The large liquid slip in organic matter (OM) also results in the apparent oil permeability of shale increases with the total organic content (TOC), although the fact that pore sizes within OM are universally smaller than that in IOM. This work provides a better understanding of the oil transport behaviors in a single nanopore and the nanoporous shale, and paves a feasible way to the exact numerical simulation for oil transport in nanoporous shale.