Quantitative Investigation of Colloidal Flow and Clogging Kinetics in Porous Medium Using Laser-Induced Fluorescence

Abstract

Transport phenomena of complex fluids are investigated experimentally using laser-induced fluorescence combined with macroscopic pressure measurements. A comprehensive experimental methodology was developed in order to both capture as well as quantify global and local dynamics of involved flow phenomena, over a long period of time—technical features that constitute a significant experimental challenge. This methodology is adapted for a wide range of applications. The present paper shows a typical example of use that concerns the study of clogging issue, a subject of strong interest for several geoscience applications such as geothermal energy or CO₂ storage. More particularly this work aims to study the flow of colloids in a tortuous yet permeable 2D porous medium and the consequent clogging mechanisms in a rock-like microfluidic device. Indeed, previous microfluidic studies regarding this topic generally used porous media with very simple geometries (alignment of plots), thus failing to capture the tortuous nature of real porous media that significantly affects colloid transport and retention in porous media. The averaged deposit measurements determined by image analysis and the pressure drop measurements lead to very consistent results indicating a permeability reduction due to a progressive accumulation of deposit. Local observations make it possible to identify the preferential deposition sites, to describe the mechanisms and kinetics of clogging and hence to lead to a better interpretation of the macroscopic behavior. More precisely, results show that local and global dynamics may differ. When considering the entire porous medium, specific areas of the porous network are subjected to preferential accumulation of particles while others are not, suggesting that deposition is strongly influenced by tortuosity. At the pore scale, specific retention sites at the vicinity of grains are identified, and hydrodynamics effects such as stripping are highlighted. These observations emphasize the role of the porous medium geometry on colloidal transport.