Etude numérique de l’adsorption et de la désorption de particules colloïdales en milieu poreux : Influence de la topographie de surface et des interactions physico-chimiques

Cette étude concerne le transport de particules colloïdales en milieu poreux. Les colloïdes (particules de taille caractéristique inférieure au micron) se rencontrent dans de nombreux domaines de la vie quotidienne (encre, cosmétiques, ...), de la biologie (bactéries, virus, protozoaires, ...) et de l’ingénierie (filtration, hydrologie, génie civil, génie pétrolier, ...). De par leur taille et leur nature, l’étude de ces systèmes nécessite de s’intéresser aux interactions qui peuvent exister entre les particules elles mêmes mais aussi avec le milieu environnant. On cite particulièrement le cas d’écoulements dans des aquifères qui concernent le transport de contaminants d’origine biologique (bactéries, virus), d’origine chimique (hydrocarbures, polluants) ou d’origine minérale (argiles, métaux, ...). Dans chacun des cas cités, il est nécessaire de s’intéresser au transport et dépôt/décollement des particules pour mieux comprendre et modéliser les mécanismes mis en jeu. Une première partie du travail est consacrée à la mise en place et à la résolution d’un modèle macroscopique de dépôt de particules. La comparaison des résultats numériques avec des données expérimentales de la littérature a permis d’établir les relations existantes entre le facteur de retard et la force ionique d’une part et le nombre de Péclet d’autre part. La seconde partie du travail concerne l’étude, à l’échelle microscopique, du transport de particules colloïdales en présence de rugosités de surface (obstacle ou cavité). Les résultats mettent en évidence le rôle joué par ces rugosités de surface sur l’adsorption et désorption de particules sous l’influence des forces hydrodynamiques et des interactions physico-chimiques.This study deals with the transport of colloidal particles in porous media. Colloids (particles with a characteristic size smaller than one micron) are found in daily life (ink, cosmetics ...) and in many fields of science and technology such as biology (bacteria, viruses, protozoa ...) and engineering (filtration, hydrology, civil engineering, petroleum engineering ...). Because of their size and nature, the study of these systems needs to focus on interactions that may exist between the particles themselves but also with the surrounding environment. This is particularly true in the case of transport of colloids in porous media where the particles characteristic dimension size is close to that of the porous medium. We mention especially the case of flow in aquifers that may affect the transport of contaminants of a biological origin (bacteria, viruses), chemical origin (hydrocarbons, pollutants) or minerals (clay, metals ...). In each case cited above, it is necessary to consider particles transport in porous media and their deposition/release to better understand and model the involved mechanisms. The first part of this work is devoted to the development and resolution of a macroscopic model of particle deposition. Comparison of numerical results with experimental data in the literature has established the existing relationships between a delay factor and both ionic strength and the Peclet number. The second part of the study deals with the study, at the microscopic level, of a colloidal particle transport taking into account DLVO forces for smooth and rough pore surfaces. Our results highlight the role played by surface roughness on the adsorption and desorption of particles under the influence of ionic strength and flow rate

Etude numérique de l’adsorption et de la désorption de particules colloïdales en milieu poreux : Influence de la topographie de surface et des interactions physico-chimiques

Cette étude concerne le transport de particules colloïdales en milieu poreux. Les colloïdes (particules de taille caractéristique inférieure au micron) se rencontrent dans de nombreux domaines de la vie quotidienne (encre, cosmétiques, ...), de la biologie (bactéries, virus, protozoaires, ...) et de l’ingénierie (filtration, hydrologie, génie civil, génie pétrolier, ...). De par leur taille et leur nature, l’étude de ces systèmes nécessite de s’intéresser aux interactions qui peuvent exister entre les particules elles mêmes mais aussi avec le milieu environnant. On cite particulièrement le cas d’écoulements dans des aquifères qui concernent le transport de contaminants d’origine biologique (bactéries, virus), d’origine chimique (hydrocarbures, polluants) ou d’origine minérale (argiles, métaux, ...). Dans chacun des cas cités, il est nécessaire de s’intéresser au transport et dépôt/décollement des particules pour mieux comprendre et modéliser les mécanismes mis en jeu. Une première partie du travail est consacrée à la mise en place et à la résolution d’un modèle macroscopique de dépôt de particules. La comparaison des résultats numériques avec des données expérimentales de la littérature a permis d’établir les relations existantes entre le facteur de retard et la force ionique d’une part et le nombre de Péclet d’autre part. La seconde partie du travail concerne l’étude, à l’échelle microscopique, du transport de particules colloïdales en présence de rugosités de surface (obstacle ou cavité). Les résultats mettent en évidence le rôle joué par ces rugosités de surface sur l’adsorption et désorption de particules sous l’influence des forces hydrodynamiques et des interactions physico-chimiques.This study deals with the transport of colloidal particles in porous media. Colloids (particles with a characteristic size smaller than one micron) are found in daily life (ink, cosmetics ...) and in many fields of science and technology such as biology (bacteria, viruses, protozoa ...) and engineering (filtration, hydrology, civil engineering, petroleum engineering ...). Because of their size and nature, the study of these systems needs to focus on interactions that may exist between the particles themselves but also with the surrounding environment. This is particularly true in the case of transport of colloids in porous media where the particles characteristic dimension size is close to that of the porous medium. We mention especially the case of flow in aquifers that may affect the transport of contaminants of a biological origin (bacteria, viruses), chemical origin (hydrocarbons, pollutants) or minerals (clay, metals ...). In each case cited above, it is necessary to consider particles transport in porous media and their deposition/release to better understand and model the involved mechanisms. The first part of this work is devoted to the development and resolution of a macroscopic model of particle deposition. Comparison of numerical results with experimental data in the literature has established the existing relationships between a delay factor and both ionic strength and the Peclet number. The second part of the study deals with the study, at the microscopic level, of a colloidal particle transport taking into account DLVO forces for smooth and rough pore surfaces. Our results highlight the role played by surface roughness on the adsorption and desorption of particles under the influence of ionic strength and flow rate

Macroscopic modeling of colloids adsorption in porous media

Natural porous media such as soils or aquifers, contain colloidal particles. Depending on geochemical and hydrodynamic conditions, they can be transported by water, developing high reactivity and mobility.They may therefore act as vectors of pollutants and viruses dissemination in soils and groundwater. Some colloidal particles like bacteria are also likely to present a risk to the environment and health. However, adsorption of colloids on the solid matrix may severely limit their mobility in porous media, consequently, their fate depends on physico-chemical and hydrodynamic conditions. Previous experimental studies [1] highlighted the role of ionic strength and Peclet number on both adsorption and release of particles. The objective of this work is to propose a macroscopic model (Darcy scale) that accurately describes the transport of colloids in the presence of adsorption process observed experimentally

Direct numerical simulation of colloid transport at the microscopic scale: influence of ionic strength in the presence of a rough surface

The way colloids are transported, deposited or detached in porous media is of great importance in many practical problems such as filtration, environmental issues, petroleum engineering, … In this work, direct numerical simulations of the transport of a single particle near the fluid/solid interface have been performed. For this purpose, new routines have been implemented in a research code in order to take into account DLVO forces for smooth and rough pore surfaces. A dimensional analysis is performed, pointing out the important role of the ratio of electrostatic forces to the hydrodynamic forces on the particle behaviour. The test cases considered are chosen on the basis of experimental results presented in the literature. Transport of a particle near a solid surface is simulated for a given Reynolds number at different values of ionic strength and the influence of various surface roughness types are analysed. The simulations illustrate three different behaviours: (i) the particle is transported by the bulk fluid (ii) the particle is adsorbed and rolls on the solid surface (iii) the particle is adsorbed by the surface and is blocked. An analysis in terms of residence time is proposed. Simulations also show that an increase in the Reynolds number leads to the mobilisation of the particle in all cases studied

On the influence of ionic strength on colloid transport in porous media in the presence of a rough surface : numerical simulation at the microscopic scale

The understanding of Colloids transport, deposit or detachment in porous media is of central importance in many practical problems such as filtration, environmental issues and petroleum engineering. In particular, the interaction of colloids with the grain surfaces is a complex problem involving combination of short range physico-chemical forces, acting at the “interface scale” with the hydrodynamics in the pore space. The understating of the processes at these small scales is crucial for the description of colloid transport processes under different physicochemical and hydrodynamic conditions at larger scales.General experimental features of colloid deposition and their detachment after a flooding with brine of ionic strength and pH different from the resident one have been reported in literature and successfully predicted using DLVO theory (Canseco et al., 2009). However and despite various efforts, such prediction remains only qualitative. It is usually believed that the observed discrepancies arise from grain or colloid heterogeneities. Such heterogeneities may concern electrostatic charge or surface topography or both.(Ducker et al., 1991; Elimelech & O’Melia, 1990).The objective of this work is to study the influence of grain surface roughness on the transport, deposit and detachment of a colloidal particle under various physicochemical and hydrodynamic conditions. For this purpose, direct numerical simulations of the transport of a single particle near the fluid/solid interface have been performed

Displacement of colloidal dispersions in Porous Media: experimental & numerical approaches

The main objective of this paper is to give more insight on colloids deposition and re-entrainment in presence of a rough surface. Experiments on retention and release of colloids in a porous medium are first presented. The influence of physicochemical and hydrodynamic conditions is investigated. The experimental results cannot be qualitatively interpreted using the DLVO theory and knowledges at pore scale are then needed. A 3D numerical simulation approach at the pore scale is therefore proposed where the motion of colloids is solved in presence of collector surfaces bearing various kinds of asperities and by taking into account physico-chemical interactions calculated at each time step during colloid movement. It is obviously observed that both deposition and mobilization of particles are dependent on solution chemistry and hydrodynamic conditions and are significantly affected by the form and size of the local roughness of the pore surface. Therefore, depending on solution ionic strength and surface topography, colloids may be adsorbed or not and when a particle is retained an increase of flow strength is then needed to remove it and such an increase is specific to the location of occurrence of the adsorption step. In general, simulation results allow us to explain our experimental results that show that by steeply increasing the flow strength, more and more fractions of particles retained inside the porous medium are released until all particles are removed