From Clogging Mitigation to Clogging Acceleration: Particle Deposition Under Oscillatory Flow in Microfluidic Porous Media.

Particle deposition and clogging in porous media control the performance of many natural and engineered applications, including groundwater filtration, geothermal injection, and subsurface fluid management. Once deposits form, permeability progressively declines and flow pathways become blocked, making mitigation strategies essential for maintaining long-term operation. Oscillatory injection has been proposed as a potential strategy to delay clogging, yet how its effectiveness depends on physicochemical conditions and complex pore geometries remains poorly understood. Here, we use microfluidic experiments with colloidal suspensions to investigate how oscillatory flow modulates particle transport and clogging in tortuous porous domains. Controlled oscillatory forcing is applied over a range of frequencies while monitoring permeability evolution and deposition dynamics. Under saline conditions, oscillatory flow delays clogging and increases the injected volume before hydraulic failure with increasing frequency, consistent with electrostatic screening that promotes particle aggregation and allows cyclic pressure fluctuations to destabilize growing deposits intermittently. However, the frequency response changes with physicochemical conditions and can even reverse. As ionic strength decreases and electrostatic interactions become stronger, aggregation is suppressed, and clogging becomes increasingly governed by particle crowding and pore bridging, where higher-frequency oscillations can instead accelerate blockage. These findings demonstrate that oscillatory injection does not have a universal effect on clogging, but instead depends on the balance between hydrodynamic forcing and particle interactions. This regime-dependent behavior provides a basis for designing more effective injection strategies in porous media.