In shale reservoirs, spontaneous imbibition is an important mechanism of fracturing fluid loss, which has an important impact on enhanced oil recovery and water resource demand. However, spontaneous imbibition behaviors are more complicated to characterize and clarify due to the nanoscale effects of the boundary slip, oil-water interfacial slip, and heterogeneous fluid properties caused by intermolecular interactions. A nanoscale multi-relaxation-time multicomponent and multiphase lattice Boltzmann method was applied to investigate the water imbibition into oil-saturated nanoscale space. The effects of pore size, fluid-surface slip, water film, oil-water interfacial slip, water bridge, and pore structures on the imbibition behaviors in a single nanopore were investigated. Then, the spontaneous imbibition behaviors in nanoporous media based on the pore scale microsimulation parameters obtained from the molecular simulation velocity results were simulated, and the effects of water saturations on imbibition behaviors were discussed. The results show that as the water saturation increases from 0 to 0.1, the imbibition mass in nanoporous media increases because of the oil-water interfacial slip and a completely hydrophilic wall. As water saturation continues to increase, the imbibition mass decreases gradually because the existence of water bridges impedes the water imbibition.

The microscale liquid flow in nanoscale systems considering slip boundary has been widely studied in recent years, however, they are limited to single-phase flow. As in nature, multicomponent and multiphase flows can also exist with non-zero slip velocities, such as oil/water slip flow in nanoporous shale. In this paper, a novel multicomponent-multiphase multiple-relaxation-time lattice Boltzmann method with a combinational slip boundary condition is developed to study the two-phase slip flow behaviors. The proposed combined slip boundary condition is derived from adjustments to the conventional diffusive Maxwell’s reflection and half-way bounce-back scheme boundary parameters, incorporating a compelled conservation requirement. With the analysis of simulations for the layer, slug, and droplet types of two-phase flow in single pores, and two-phase flow in porous media with complex wall geometry, it can be concluded that the proposed schemes of two-phase slip boundary conditions are particularly suitable for multicomponent and multiphase flow with a non-zero slip velocity. The proposed model can be used to determine relative permeability and simulate spontaneous imbibition in particular in shale reservoirs where those flow properties are hard-to-determine.

As common physical phenomena in porous media,capillarity behaviors exist in many engineering applications and natural science fields. The experimental,theoretical and numerical research on capillarity in porous media has lasted for more than a century,and the research results have been widely used in various fields,such as the development of conventional and unconventional resources. However,although the research has made great progress,the complex imbibition mechanism poses new challenges to us. The 1st National Conference on Imbibition Theory and Application in Porous Media was held in Beijing from April 22 to 24,2023, to gather researchers who are interested in imbibition research,exchange the latest progress and achievements in the field of imbibition in porous media,and discuss research hotspots and difficulties.