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Prediction Of Colloidal Particle Deposition In Consolidated, Homogeneous Porous Medium Using The Non-destructive Technique

Congress: 2015
Author(s): Abdelkader Djehiche ( Laghouat,, Algeria)


Keyword(s): Sub-theme 2: Surface water and groundwater,
AbstractIntroduction In porous media the deposition of colloidal particles in flowing suspensions is a challenging problem in both scientific and industrial interest. Many applications can be found in fields such as of Petroleum, Hydraulic engineering, deep-bed filtration, a unit operation commonly used in water treatment to remove fine particles, pathogens and colloid-associated pollutants from dilute suspensions (Ires and Gregory, 1967; Yao et al., 1971; O'Melia, 1985, M. Elimelech, 1992). The extent of migration of colloidal materials (e.g. viruses, bacteria, humic colloids and metal oxides) and colloid-bound pollutants in ground waters and soils is also controlled by the processes of colloid deposition. In all cases, colloid particles suspended in the flowing liquid can be captured by the surrounding solid walls of the pore space, with, some deposits occurring gradually inside the porous medium. This deposit formation phenomenon creates two problems. First, it can drastically increase the local concentration of pollutant particles. Second, gradual fouling of the porous medium occurs in some regions, considerably reducing the permeability of the porous medium (I. Gohr Pinheiro et al., 1999). These modifications have on a large scale an important consequences on the physical phenomena, thus it is necessary to characterize these conditions properly. This phenomenon depends mainly on particle--particle and particle--pore solid wall interaction potential and on hydrodynamic conditions. In the present study, we present an experimental study of transport and deposit of colloidal particles in a consolidated, homogeneous porous medium and initially saturated with water. The liquid phase injected into an artificial consolidated porous medium is a suspension of latex particles whose dimension is known. We used a non-destructive gamma-ray attenuation technique which is able to provide this information by probing local porous medium damage (D. Gharbi, et al., 2004). A method of global measurement by pressure drop was also used to determine the permeability reduction of the porous medium. The two methods were used in presented in the present work. The first results obtained show a good agreement between local and global measurements of the deposit of the particles in porous medium. The deposit takes place in a progressive way along the porous medium and leads to a monolayer deposit with an average thickness in same order of the colloidal particles diameter magnitude. 1 Experimental setup An artificial consolidated porous medium was used (Aerolith-10). Its initial porosity and permeability were 0,40 and 10 Darcies, respectively. The 15 cm long sample was a cylindrical core of 5 cm diameter, The lateral surface of the porous medium was coated with a nonwetting epoxy resin then wrapped with epoxy-coated fibreglass to insure liquid imperviousness, mechanical strength and a good gamma-ray transparency. The colloidal suspension is a bi-disperse polystyrene latex particle suspension, was used (averaged diameter of 780 nm). The concentration of the colloidal suspension was settled to 200 ppm. Fig. 1 : Experimental setup The central piece was the porous medium positioned horizontally in the rig displacing the porosity measurement device. A volumetric pump was used to inject brine or colloidal suspension. Three differential pressure transducers (0--0.9 mbar) were positioned along the core (three 5 cm long sections) to measure the pressure drop along the core and to determine the permeability. The colloid concentration in the effluents was measured by spectroscopy, as shown in figure one. The porous medium is saturated with brine and the initial values of permeabilities and field of local porosity were measured. The colloidal suspension is then injected with constant flow, corresponding to predetermined Péclet. A regular collection of the effluents is carried out, results of measurement of the latex concentration by spectroscopy are presented in Figure 2. At different stage from the process, the injection of the suspension is stopped and was immediately followed by a brine injection to move the particles not deposited. Which can allow us to measure the faded medium field local porosity and permeability. These results were interpreted and the thicknesses of hydrodynamic layer was calculated, and presented in Figure 3. Several experiments with various flows rate were carried out, and all show the dependence of the deposit of particles with respect to the number of Péclet. For low values of Pe, the deposit is carried out in the form of monolayer of particles covering the near total of surface porale. When the number of Péclet increases, the deposit of particles becomes less dense. Conclusions and prospects In this study we show that non-destructive experimental technique used (attenuation of the gamma radiation) and adopted methodology allow the space monolayer of the deposit of particle in any point of the porous medium. Moreover, the local character of measurement was an asset to appreciate the effective damage of the porous medium whereas the usual methods were destructive or intrusive also gives only indirect measurements of the global damage through the medium of permeability fall. We highlighted that the deposit is carried out in a progressive way along the porous medium until obtaining of a monolayer deposit. Among the prospects for this work initially appears the follow-up of the formation of the deposits into multi-layer and the influence of the ionic force and the conditions of flow on the process of adsorption of the colloidal particles. Fig. 2 : Latex concentration in the effluents according to the volume of suspension injected. 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