Mechanisms of displacement–imbibition coupling in shale reservoirs: Physical experiments and three-dimensional lattice Boltzmann modeling

Displacement–imbibition oil production is regarded as a promising technology to enhance the oil recovery (EOR) of shale oil reservoirs. To investigate the microscopic mechanisms and flow behaviors governed by pore–throat structures and fracture types, we first performed single-phase core displacement experiments to characterize the nonlinear flow responses. Subsequently, a real-time physical simulation apparatus for displacement–imbibition was independently designed based on nuclear magnetic resonance (NMR) technology. This setup enabled the characterization of realistic fracture morphologies in artificial cubic cores, and the systematic examination of the influence of fracture types on oil production. Finally, a three-dimensional lattice Boltzmann model incorporating nonlinear flow characteristics was developed for the injection–shut-in–production process to investigate oil–water flow dynamics at the pore scale. The results show that pressure oscillation and capillary imbibition are the key drivers of oil production. By altering the pressure field of matrix pores, the combined driving forces of displacement and imbibition lower the utilization threshold of pore-throat and achieve more uniform pore utilization. The pore–throat structure governs efficiency, as porous media with weaker nonlinear flow effects and stronger connectivity exhibit lower resistance to oil–water exchange. Fractures significantly influence fluid exchange, and the more complex the contact between the matrix and fractures, the easier it is for oil to be displaced. Maximizing the effect of displacement–imbibition while avoiding water channeling is essential. These findings enhance understanding of multiphase displacement dynamics and support water-injection EOR technologies.