PhD defense Walid Okaybi

Colloidal transport in porous media plays a central role in subsurface systems, including groundwater resources, geothermal energy, and underground thermal energy storage. Suspended particles may originate from the porous formation or be introduced with injected fluids. Their transport and retention within the pore space can lead to clogging, thereby reducing permeability and injectivity. In injection-based applications, these processes may be further enhanced by physicochemical and hydrodynamic differences between injected and native conditions.
However, pore-scale clogging mechanisms remain poorly understood in heterogeneous porous media representative of natural systems due to their opacity, which limits direct observation of key processes. To address this limitation, this work combines microfluidic experiments in heterogeneous porous media with image analysis and pore-scale flow simulations to investigate and identify the mechanisms governing particle deposition, clogging, flow alteration, and permeability evolution across distinct deposition regimes and under varying physicochemical and hydrodynamic conditions. The results show that clogging is a regime-dependent process governed by distinct mechanisms. Under adhesive conditions, a novel form of progressive clogging is identified, in which dendritic structures grow from a single preferential deposition site and progressively block the pore space. This mechanism is controlled by local flow conditions, particularly the size of stagnation regions relative to particle diameter. Under repulsive conditions, clogging is dominated by hydrodynamic bridging, where particles form stable arches at pore constrictions, leading to stepwise permeability reduction controlled mainly by particle size and concentration. Oscillatory flow does not systematically mitigate clogging, but instead produces a regime-dependent response: it can delay clogging in aggregation-dominated conditions, yet accelerate it at higher frequencies in hydrodynamic regimes. Overall, this work provides new insight into the mechanisms controlling colloidal clogging and highlights the need for a regime-dependent approach to predict and manage permeability reduction in realistic subsurface systems.