Characteristics of pore-scale events and their impact on transport in porous media

Pore-scale events (PSE) such as Haines jumps, meniscus reconfiguration, and meniscus merging are commonly observed during immiscible fluids displacement in porous materials. However, the impact of these interfacial dynamics on the governing two-phase displacement at the network scale remains underexplored, as do their energy scale and frequency characteristics across varying relative importance of capillary and viscous forces. This study uses direct numerical simulations to investigate PSEs in a two-dimensional (2D) heterogeneous micromodel across a range of capillary numbers (Ca) and viscous ratios (M), including both favorable (logM > 0) and unfavorable (logM < 0) displacement scenarios. These simulations incorporate the characteristics of the three typical two-phase displacement patterns: stable displacement, capillary and viscous fingering. The PSE impact on transport in porous media is quantified by mechanical energy, especially viscous dissipation. The results showed that PSEs markedly reduced two-phase flow mobility in porous media at low Ca, while this impact decreased with increasing Ca and disappeared at near high Ca. Meniscus merging considerably increased the viscous dissipation rate in the displacement at low, medium, and high Ca values, but it exhibited a markedly lower frequency than Haines jump and meniscus reconfiguration. In favorable condition, the impact of Haines jump and meniscus reconfiguration on displacement viscous dissipation rate disappeared at medium Ca, whereas in unfavorable condition, it disappeared until high Ca. This resulted from the strengthened interfacial interaction caused by the liquid film generated in the front of the viscous fingering. Overall, based on mechanical energy conservation, this study provides insights into PSE characteristics and impact under different conditions, which could help solve long-standing fundamental questions associated with transport and flow in porous materials.