Transport and Clogging of Colloidal Particles: Effects of Concentration and Geometry of The Porous Medium.

Geothermal fluids are often loaded with mineral and organic particles in suspension, dissolved organic and mineral compounds, various additives, bacteria and heavy metals, etc. These compounds pose significant problems on the sustainability of production and the maintenance of injectivity in the short term and, in the long term, on the stability and continuity of the resource. As the migration and deposit of fines concern numerous industrial applications, the physics of colloidal particles in porous media has been widely studied. However, most of these studies are based on macroscopic measurements, mostly with corefloods. Since these media are opaque, we lack information on the mechanisms involved at the pore scale.

Lately, studies on transport mechanisms at pore scale with microfluidic devices have expanded due to their importance in many engineering applications such as oil and gas production, groundwater pollution or wastewater treatment. Micromodels are 2D-microstructures made of transparent materials that allow us to visualize directly the phenomena involved at the pore scale. Moreover, during the microfabrication process, the etching pattern can be designed according to the research objectives. Hence, we work with micromodels representative of a rock-like porous medium that have similar intrinsic properties (permeability, porosity, geometry of the pores…). Thanks to microfluidic tools, the aim of this work is to describe the characteristics of permeability damage process associated to particles retention in porous media during the reinjection of geothermal fluids.

This study is based on the complementary information obtained with two experimental set-ups based on different visualization techniques: optical imaging and laser-induced fluorescence (LIF) imaging. Both systems have been designed to integrate the following tools: particle concentration monitoring, pressure drop kinetic, direct visualization of the micromodel in which the fluids are injected. The use of these two technics allows us to access complementary information at various scales: with fluorescence, we obtain the concentration field that includes the depth of the micromodel whereas with classical optical imaging we obtain a better resolution of the images and therefore a better understanding of the mechanisms.

Eventually, our experimental study allows us to establish a link between the permeability reduction and the impact of physicochemical factors such as flow rate, injected particle size or surface functionalities on particles retention within the porous medium. The connection is established between the velocity field related to the geometry of the porous medium and the characteristics of the deposit.