Micromodel Study on Colloid Retention and Mobilization under different Geo-Chemical Conditions during Single and Two-Phase Flow

Abstract

Understanding the transport of colloids and colloid-facilitated transport of contaminants is essential for efficient cleanup and remediation processes. Various factors and mechanisms contributing to their retention in the porous media have been studied indirectly through laboratory column breakthrough analysis and directly using visualization studies. Micromodels are analogs to porous media that allow the real-time visualization of pore-scale processes that occur at highly controllable physio-chemical conditions in the laboratory scale. In this thesis, we used a glass micromodel with representative geometry to observe the pore-scale mechanisms during colloid retention and mobilization experiments in a saturated and unsaturated porous media. The focus of this research was to investigate the colloid retention mechanisms under different physio-chemical conditions such as variable colloid type, solution ionic strength, and solution pH. Various colloid retention sites in unsaturated porous media were identified from the captured images and videos during drainage (using CO2 gas ) in a saturated micromodel. Quantitative analysis of colloid mobilization was performed using image-processing algorithms on a Representative Elementary Area (REA) image of the micromodel before and after drainage. This study also investigated colloid mobilization from AWI during imbibition in porous media. The impact of colloid hydrophobicity on mobilization was observed in a micromodel. The visual findings explained with the theoretical conceptualization of the forces acting on a colloid at AWSI. The colloid reattachment on SWI found during the dissolution of the gas bubble for hydrophilic colloids due to their greater capillary potential. Whereas, the lifting-capillary forces on hydrophobic colloids resulted in aggregation of excess colloids on AWI. This study also examined the retention and release of colloids under the influence of perturbations in flow rate and solution chemistry. The retention of three different types of colloids (i.e., favorable, unfavorable, and medium favorable conditions) was observed visually in a micromodel. The pore-scale visualizations reveal the impact of colloid deposition profile on colloid release with an increase in flow rate and solution pH as well as a decrease in solution ionic strength. The results from this study show the dependence of favorability of interaction conditions on colloid deposition profile as well as the colloid release during hydro-chemical perturbations in saturated porous media. This dissertation accompanied by supplementary material showing video images of the illustrated processes