Caractérisation d'un milieu poreux colmaté par la méthode du potentiel spontané

Laboratory experiments are performed on the physical clogging of a porous medium by injecting polydispersive suspended particles ranged from 1.7 to 40 μm in a column filled with sand (d50=715 µm). Three suspensions have been injected (2g/l, 3g/l and 5g/l) at constant flow velocity in a saturated porous medium. Hydrodynamic effects on particles deposition and porous medium damage were investigated. Particles retentions are significant at the inlet and decreases with depth which induces the drop of permeability and porosity. The coupling between electric and hydraulic flows is electrokinetic in nature, the second objective of this work is to test the sensitivity of the method of self-potential (SP) and to show the usefulness of this method to understand the controlling parameters of the electrical field associated with the filtration of suspended particles through a porous medium. Electrodes have been used to record the SP signal which detect and quantify the clay particles in the porous medium during injection tests. The variations of the SP signals are linearly correlated to the piezometric level changes. SP signals are directly sensitive to deposition particles distribution, and it is high at the inlet of the column where the deposit is large and decreases with depth. For the test injection with 2g/l the SP signal varies between +16 mv and +13 mv for the test with 3g/l it varies between +12 mv and +8mv and that with 5g/l it varies between - 22mv to-19mv. When the concentration of clay injected in the porous medium increases, the SP signal decreases and changes from a positive sign to a negative sign. SP method confirmed the behavior of the porous medium clogging obtained by the hydraulic measurements. The obtained results show that SP signal is sensitive to clay particles, their immediate passage to the inlet of the column and the amount deposited particles in each section of the porous medium

Étude des mécanismes de transport et la cinétique de dépôt des particules en suspension dans un milieu poreux saturé

LE HAVRE-BU Centrale (763512101) / SudocSudocFranceF

Hydraulic Operating Conditions and Particle Concentration Effects on Physical Clogging of a Porous Medium

International audienceThe effects of the hydraulic operating conditions and the concentration of suspended particles (SP) in pore fluid on the filtration and physical clogging of a porous medium were investigated. Polydisperse kaolinite SP was injected into a sand-filled column under two different operating conditions: constant flow rate and constant head. The retention rate was observed to be greater under the condition of constant head than under the condition of constant flow rate, mainly for the high concentrations. Under constant head, the porous medium were clogged more rapidly; the pore velocities decreased with time and the permeability reduction occurred in fewer pore volumes injected than under constant flow rate. Under the same hydraulic condition, an increase of the concentration leads to a more rapid reduction in permeability. Regardless of the hydraulic operating conditions, particle-size analysis shows an increase with time of the median diameter of the particle-size distribution of the recovered particles. At the beginning of the filtration process, larger particles are mainly retained in the column. As the injection volume increases, the larger particles are better transported and the size of particles observed in the effluent gradually increases. It appears that the median diameter of the recovered SP increases more rapidly with time under constant flow rate

Influence of Internal Structure and Medium Length on Transport and Deposition of Suspended Particles: A Laboratory Study

International audienceA laboratory study was undertaken on the transport and the deposition of suspended particles (silt of modal diametre 6 µm) in three columns of different length, filled with glass beads or gravel. Tracer tests were carried out at various flow velocities by short pulses of a mixture of suspended particles/dissolved tracer. The breakthrough curves were competently described with the analytical solution of a convection dispersion equation with a first-order deposition rate and the hydro-dispersive parameters were deduced. For the same experimental conditions, the results showed a difference in the behaviour of the suspended particles transport and deposition rates within the two porous media tested. The internal structure of both media governs the particle-grain collision frequency as well as the particles trapping. The scale effect was highlighted and affects the dispersivity, the size exclusion effect, the recovery rates and the deposition rates. Longitudinal dispersion increases with mean pore velocity and is described with a nonlinear relationship. The dispersivity increases with the column length. The size exclusion effect is more important in the short column. The recovery rate increases with flow velocity and decreases while increasing column length. The deposition rates increases until a critical flow velocity then decreases. This critical velocity is also sensitive to the scale effect, and increases with the column length

Coupled Effects of Ionic Strength, Particle Size, and Flow Velocity on Transport and Deposition of Suspended Particles in Saturated Porous Media

International audienc

Effects of Particle Size Non-Uniformity on Transport and Retention in Saturated Porous Media

International audienc

Particle transport in a saturated porous medium : pore structure

This paper presents an experimental study of the transport of suspended particles (SP) in a saturated porous media, aimed at delineating the effects of pore structure on particle transport and deposition rate. Two porous media (silica gravel and glass beads) and silt SP were used. Breakthrough curves (BTCs) were well described by analytical solution of an advective-dispersive equation with a first-order deposition kinetic. The recovery rate of suspended particles is higher in the glass beads even if the porosities are similar. This study shows the importance of pore distribution in transport processes of suspended particles

Contribution of the transport of suspended particles to the internal erosion in soils: Particle migration in porous media

National audienceAn experimental study which aimed at investigating the transport behaviour of suspended particles in saturated porous media is presented. A short-pulse technique was used for measuring particle recovery and collision efficiencies in two porous media (silica gravel and glass beads). Breakthrough curves (BTCs) were measured on-line and well described by analytical solution of an advective-dispersive equation with a first-order deposition kinetic. The effects of hydrodynamic and gravity forces on particle transport and deposition rate were delineated. Results show particles travelling faster than the conservative tracer. The recovery rate of the suspended particles decreased with decreasing flow rate, and the deposition rate presents unexpected changes, depending on the flow rate

Filtração de partículas de caulinite num meio poroso saturado: efeitos hidrodinâmicos

International audienceA study was undertaken on physical clogging of a porous medium by injecting suspended particles (SP), ranging in diameter from 1.7 to 40 μm, into a sand-filled column. Long-term tracer tests were carried out at various flow velocities. Retention of the SP is significantly influenced by the flow velocity. At low flow velocities, retention is confined to a limited length of porous medium, from the entrance of the column, leading to a substantial modification of the hydraulic characteristics of the porous medium. However, at high flow velocities, a much greater length of the porous medium is affected. Particle-size analyses indicate that the particle-size distribution (PSD) of recovered particles changes with time, while the PSD of retained particles changes with depth and time. At the beginning of the filtration process, larger particles were mainly retained at the column entrance. As the injection volume increases, the larger particles penetrate more deeply into the porous medium, and the size of particles observed in the effluent gradually increases. This study highlights the influence of flow velocity, duration of filtration, and the particles’ polydispersity, on the hydraulic characteristics of the porous medium