Interfacial jumps and pressure bursts during fluid displacement in interacting irregular capillaries.

The macroscopically regular motion of fluid displacement fronts in porous media often results from numerous pore scale interfacial jumps and associated pressure fluctuations. Such rapid pore scale dynamics defy postulated slow viscous energy dissipation and may shape phase entrapment and subsequent macroscopic transport properties. Certain displacement characteristics are predictable from percolation theory; however, insights into rapid interfacial dynamics require mechanistic models for hydraulically interacting pores such as found along fluid displacement fronts. A model for hydraulically coupled sinusoidal capillaries was used to analyze stick-jump interfacial motions with a significant inertial component absent in Darcy-based description of fluid front displacement. High-speed camera provided measurements of rapid interfacial dynamics in sintered glass beads cell during drainage. Interfacial velocities exceeding 50 times mean front velocity were observed in good agreement with model predictions for a pair of sinusoidal capillaries. In addition to characteristic pinning-jumping behavior, interfacial dynamics were sensitive to initial positions within pores at the onset of a jump. Even for a pair of sinusoidal capillaries, minute variations in pore geometry and boundary conditions yield rich behavior of motions, highlighting challenges and potential new insights offered by consideration of pore scale mechanisms in macroscopic description of fluid displacement fronts in porous media.