SC3 - Microfluidics supporting preserved injectivity

Injectivity in geological formations has long been an important factor in oil production (enhanced recovery) but it is now just as important in fields related to new energies and the climate (geothermal energy, CO₂ storage, etc.). Injectivity losses, which result from the clogging of geological formations, are a recurrent problem associated with the fact that reinjected water often carries a high concentration of organic and mineral elements in suspension, in the form of colloidal particles.

To remedy this clogging, or at least minimize it, it is important to clearly understand the mechanisms involved. 

The phenomenon of particle transport and deposition in porous media has been extensively studied in the past, particularly through coreflood permeability measurements. Its quantitative impact on this property is thus well established but, due to rock opacity, less has been known about the mechanisms taking place at pore scale.

In recent years, advances in imaging and visualization tools have enabled researchers to study phenomena at the pore scale. Coupled to microfluidics, a methodology allowing the control and use of very small volumes of fluids¹ in confined microstructures, key results on clogging dynamics have been obtained. Moreover, recent developments in engraving techniques enable researchers to reproduce the complexity of real porous media in these microstructures. By combining all these techniques, it is possible to directly visualize the flow in order to more accurately describe the phenomena involved on a local scale.

During thesis research carried out at IFPEN² in partnership with ICMCB³, the problem of deposition and clogging was studied using a microfluidic approach combining two visualization techniques: optical imaging [1] and laser-induced fluorescence [2]. The micromodels used (Fig. 1(a)) feature geometries inspired by images of real rock pore networks. A model suspension of micrometric particles with repulsive charges⁴ was used. Combining multi-scale observations (Fig. 1(b), (d)) and macroscopic measurements (pressure and concentration) (fig. 1(c)) has enabled to characterize in detail the mechanisms acting at the pore scale and to gain a better understanding of the phenomena at play, depending on both hydrodynamics (velocity, pore geometry) and particle-particle and particle-solid matrix interactions (DLVO forces⁵).

By cross-referencing the characteristics of the deposits obtained experimentally with the velocity fields determined by numerical simulation, this study, carried out under geothermal fluid reinjection conditions (small particles, high flow rate, permeable porous media), enabled the identification of the various deposition sites and regimes, as well as the description of clogging mechanisms. One of the most significant results obtained was the demonstration of a shear-induced aggregation phenomenon [3]. Deposition sites, which represent traps primarily governed by streamlines in the porous medium, generate a local overconcentration of particles according to five configurations: in the wake of a solid grain, at stagnation points, in flow-free regions, at the confluence of two local flows or at the entrance to a narrow pore. This local over-concentration of particles, when combined with significant local shear⁶, induces formation of aggregates.

The phenomenon of hydrodynamic aggregation is closely correlated with high injection rates and presents a major risk that needs to be anticipated and controlled. In fact, these irreversible aggregates can form even when fluids are finely filtered and contain very few particles. They are easily carried along in the flow, without breaking up, leading to clogging at pore thresholds via geometric exclusion, the aggregates being too large to circulate.

The kinetics of this damage were studied as a function of particle concentration, particle size and injection rate. Interpretations based on local observations and highlighted mechanisms were then proposed. Finally, the main results obtained using microfluidics were validated for more real systems (for example, a suspension of polystyrene particles in reconstituted sand beds or clay particles in micromodels) and paved the way for potential solutions to the phenomenon.
  

¹- Order of magnitude of a microliter or even a picoliter.
²- Anne-Sophie Esneu, Etude des mécanismes d’endommagement des formations lors de la réinjection des fluides géothermiques (Study of formation damage mechanisms during geothermal fluid reinjection), Bordeaux University, 2024.
³- Bordeaux Institute for condensed matter chemistry - UMR CNRS 5026
⁴- To avoid aggregation prior to injection. 
⁵- Derjaguin, Landau, Verwey, Overbeek.
⁶- Shear consecutive to fluid flow in the presence of a random arrangement of grains.
        

References:

1. A.-S. Esneu, C. Marlière, L. Nabzar, A. Erriguible, S. Glockner, S. Marre and J. Boujlel. Transport and clogging of colloidal particles: effects of concentration and geometry of the porous medium. In Proceedings of World Geothermal Congress 2023, Beijing, China, October 2023.
     

2. A.-S. Esneu, V. Ricordeau, A. Perez, G. Pilla, M. Bardi and J. Boujlel. The use of Laser-Induce Fluorescence Imaging to investigate transport phenomena of complex fluids in a 2D porous medium. To be submitted in Transport in Porous Media
     

3. A.-S. Esneu, A. Erriguible, S. Glockner, S. Marre and J. Boujlel. 2D heterogeneous porous medium permeability reduction by shear-induced aggregation. To be submitted in Physics Review Letters. 
         

Scientific contacts: anne-sophie.esneu@ifpen.fr and jalila.boujlel@ifpen.fr

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