Lattice Boltzmann Model for Oil/Water Two-Phase Flow in Nanoporous Media Considering Heterogeneous Viscosity, Liquid/Solid, and Liquid/Liquid Slip

Summary Due to intermolecular interactions, the oil/water two-phase flow behaviors in shale nanoporous media are complex and diverse, which cannot be characterized by a conventional continuum flow equation. In this work, we propose a nanoscale multirelaxation-time multicomponent and multiphase lattice Boltzmann method (MRT-MCMP-LBM) based on pseudopotential format to simulate oil/water two-phase flow at the pore scale. The nanoscale effect of liquid/solid slip, liquid/liquid slip, and heterogeneous viscosity due to liquid/solid and liquid/liquid molecular interactions is fully taken into account. We use the Laplace test, contact angle, and phase separation to calibrate the desired interfacial tension (IFT) and wettability. Then, the proposed model is verified by comparing to molecular simulation and theoretical results. Although the liquid/solid slip can increase the oil/water flow capacity, it can reduce the relative permeability due to the increased intrinsic permeability. The oil/water interfacial slip can increase the relative permeability of the nonwetting phase, which can be greater than unity because the effect of oil/water interfacial slip is greater than that of nonwetting-phase/wall slip. We also calibrate the microscopic parameters of oil and water flow in inorganic and organic pores by comparing their velocity profiles to those from molecular dynamics (MD) simulations. The oil/water two-phase flow in shale nanoporous media indicates that with a higher total organic carbon (TOC) content, oil relative permeability is lower due to the more significant adverse nanoscale effect. The proposed model can be potentially applied to simulate shale oil/gas/water multicomponent and multiphase (MCMP) flow, imbibition, CO2 huff ‘n’ puff, and geological sequestration.