Karim Bekkour

Abstract:

Abstract: We examined the changes in the physical properties of the digesta mat over a period of 24 h after cessation of feeding, in sheep that had been maintained on pasture or fed chaffed lucerne hay. The dry matter content of the digesta mat declined at similar rates in both dietary groups, although it was generally higher in sheep fed lucerne. Median particle size declined in the digesta mats of both dietary groups at similar rates in samples taken after 8 h, but median particle size was significantly greater in sheep fed chopped lucerne hay than in those fed grass. Thus, particles were not reduced to a common size suggesting that factors in addition to particle size governed the rate of breakdown of the rumen mat. The relationship between the elastic and loss moduli was of a consistent pattern in all samples taken from the rumen mat indicating that it behaved as a weak gel. The elastic and loss moduli of the digesta mats of sheep that had been fed pasture or chopped lucerne hay converged to similar values after 12 h and declined broadly at similar rates after this. The relationship between these two moduli and the dry matter content of the rumen mat were of similar curvilinear form for sheep on both diets. These findings suggest that the rate of breakdown of the rumen mat is more likely to be governed by its composite behaviour than by the size of the constituent particles.

Abstract: In this work,we consider model fluids which are dispersions of clay particles in aqueous solutions of carboxymethyl cellulose. Their rheological properties are measured in both steady and oscillatory shear flows.We present the experimental results obtained for different polymer concentrations and for three different molecular weights of the polymer. The clay is a bentonite sample and the particle concentration is fixed to a value of 5 %. The mechanical properties of these materials is the result of a competition between different mechanisms: association-dissociation of aggregates of particles, adsorption of polymer on the particles and desorption of solvent molecules from the particles, bridging of the particles by long polymer chains.

Abstract: The rheological properties of aqueous solutions of poly(ethylene oxide) (PEO) of different molecular weights (1 � 105, 4 � 105, 1 � 106 and 4 � 106 g mol�1) and concentrations were investigated using shear viscosity and dynamic rheological measurements. It was found that the aqueous solutions of PEO do not exhibit a yield stress and that, above a critical shear rate, all PEO solutions exhibit shear-thinning behavior, well described by the Cross model, except for the solutions made by the lowest molecular weight (1 � 105 g mol�1) which were almost Newtonian. The parameters of the Cross model, namely the zero-shear rate viscosity and reciprocal of the time constant, allowed the determination of the critical concentrations c* and c** (respectively, the transition to semi-dilute network solution and concentrated solution). At concentrations higher than c** and below a critical shear rate, solutions made of PEO of high molecular weight exhibited a clearly shear-thickening behavior at very low shear rates. In addition, the dynamic tests showed that PEO solutions exhibit concentration-dependent viscoelastic properties, with a dominant viscous behavior at PEO concentrations lower than c** and a dominant elastic behavior at PEO concentrations greater than c**.

Abstract: This paper describes a velocimeter, based on back-scattering of ultrasonic waves by particles, designed for velocity measurement of suspended sediments within the flow of sewer systems. The Ultrasound Pulse Doppler Velocimeter (UPDV) needs no calibration and is therefore a potentially useful tool for measuring velocities in laboratory experiments or in sewer systems. The potential of the developed system to determine the velocity in turbulent pipe flow was investigated. Two different approaches were used to estimate velocity: the well-known temporal method, i.e., the Pulse-Pair technique and the spectral identification based method, developed by our research group. Measurements have demonstrated the ability of the apparatus, on the one hand, to measure unsteady turbulent velocities, and on the other hand, to investigate experimentally the statistical properties of homogeneous and isotropic turbulence. A good agreement between experimental results and theory was observed. The validation of these laboratory measurements permits to extrapolate them to sewer systems.

Abstract: In this study, we investigated the way of predicting two critical concentrations of sodium carboxymethyl cellulose (CMC) solutions using simple experimental procedures with a rotational rheometer. It was found that, above a critical shear rate, all CMC solutions (0.2 to 7 wt.%) exhibit shear-thinning behavior and the flow curves could be described by the Cross model. A first critical CMC concentration c*, transition to semidilute network solution, was determined using the following methods (1) study of the flow curve shapes, (2) Cross model parameters, (3) plot of the specific viscosity vs the overlap parameter, and (4) empirical structure�properties relationships. Furthermore, both creep and frequency-sweep measurements showed that the solutions behaved as viscoelastic materials above a second critical CMC concentration c** (transition to concentrated solution). The characterization of CMC solutions was completed with a time-dependent viscosity study that showed that the CMC solutions exhibited strong thixotropic behavior, especially at the highest CMC concentrations.

Abstract: Three different experimental measurements, namely, rheology, particle sizing, and x-ray diffraction (XRD), were used to study the effect of anionic additives on the properties of bentonite suspensions. The three additives were sodium carboxymethylcellulose, xanthan gum, and sodium dodecyl sulfate. Flow curves were obtained from shear stress�shear rate measurements, and the viscoelastic properties were determined from oscillatory and transient measurements. Mineralogical data were evaluated by XRD and the particle size analysis performed by light scattering technique. The presence of the surfactant modifies the face-to-face interactions and yields changes of the mixtures rheological behavior at low deformation rates. Polymers act by coating each clay particle and prevent their agglomeration. Therefore, the additives are responsible for the mechanisms of destructuration and structure reorganization as well as the mixtures viscous and viscoelastic behavior.

Abstract: The thixotropic behavior of bentonite suspensions was studied using different experimental procedures. It was found that the bentonite dispersions exhibit a time-dependent non-Newtonian behavior. In addition to the major factors affecting the rheological properties in the dispersion were the shearing value and duration, the rest time preceding the measurements and the structural state of the dispersion. The Herschel�Bulkley model was found to correlate well with the behavior of bentonite suspensions. The time evolution of the shear stress at constant shear rates was correlated by the Bird�Leider equation. In order to take into account structural evolution of the suspensions, the rheological law was modified by the introduction of the phenomenological model of Tiu and Boger derived from Moore's kinetics evolution. It was observed that at short rest times and low shearing conditions, this model describes satisfactorily the time-dependent behavior of the bentonite suspensions. The behavior laws and kinetics evolution were established through the determination of structure destructuration and reorganization rates values. The structure parameters were found to be dependent on the clay concentration, providing evidence that the scale characteristic times of the buildup and breakdown processes are also concentration dependent.

Abstract: Le déroulement normal des opérations de forage du champ de Hassi-Messaoud et plus précisément celui de la phase 8��1/2 est très souvent interrompu par plusieurs problèmes englobant la tenue des parois du trou, les pressions rencontrées et le contrôle des fluides contenus dans les formations forées. Dans ce contexte, le travail entrepris consistait essentiellement en la préparation de laitiers colmatants contre les pertes de boues et de cavage. Les pertes en circulation sont la conséquence logique d�un déséquilibre de pression, existant ou créé, momentané ou permanent, entre le milieu traversé et les fluides utilisés en forage. Afin d�y remédier, des bouchons de ciment sont souvent utilisés pour colmater ces pertes. Lors de la rencontre de pertes importantes, on arrive à installer plus de six bouchons de ciment, ce qui est un inconvénient majeur pour l�avancement de l�opération de forage en terme de temps et de coût. La solution proposée est l�injection d�un seul "bouchon de type plastique", ajustable suivant la fréquence des pertes, allant de simples fissures aux fractures. Ce type de bouchon est à base d�une variété d�argiles. Une caractérisation et une modélisation du comportement rhéologique de ces argiles ont été effectuées. Trois systèmes de laitiers ont été considérés : un laitier formulé, où l'on observe un excès de phase aqueuse après mélange des composants, et que l�on appellera "direct"; un autre laitier formulé, où l'on observe un excès de phase huileuse, que l�on appellera "inverse"; et enfin, le laitier caractérisé par l�absorption totale des composants, qui se présente sous forme d�une pâte consistante de type mastic, que l�on nommera "mixte". Il a été confirmé que les formulations de ces bouchons, préparées en conditions de surface, présentent les mêmes caractéristiques qu�en conditions de fond. Ceci a été nettement observé suite aux tests de consistométrie. Les réactions de prise de ces bouchons sont instantanées dans les deux cas, avec un simple brassage des différents composants du mélange. Une procédure appropriée est recommandée pour l�injection de ce type de bouchon.

Abstract: Les mousses étudiées sont à base de surfactant, le SDS (Sodium Dodécyl Sulfate), et d'un polymère, le PEO (Poly Ethylène Oxyde), à différentes concentrations. Un rhéomètre à contrainte imposée a été utilisé pour la mesure de leurs propriétés rhéologiques. L'étude de l'écoulement sous l'effet d'une contrainte imposée a mis en évidence un comportement hystérétique avec des rhéogrammes présentant un point d'inflexion (passage d'un comportement rhéofluidifiant à un comportement rhéoépaississant) pour une valeur donnée de la vitesse de cisaillement. La viscosité apparente décroît avec le vieillissement et le temps de montée en contrainte. Des mesures en mode oscillatoire ainsi que des mesures de fluage ont été effectuées pour sonder la réponse viscoélastique des mousses et un modèle phénoménologique (Kelvin-Voigt généralisé) est utilisé pour décrire les résultats obtenus.

Abstract: An experimental study of steady shear flow properties of foams prepared with sodium-dodecyl-sulfate (SDS) as surface-active agent and poly-ethylene-oxide (PEO) as stabilizer was performed. Differences in foam stability were clearly observed. It was found that the characteristic time t1/2 and thus, the stability of the foam increases with the concentration of PEO.

Abstract: Bentonite are extensively used materials in a wide range of applications. Creep and oscillatory shear experiments in the linear viscoelastic domain were carried out on bentonite-water suspensions at different solid fractions. It was found that bentonite dispersions exhibit important viscoelastic behavior which could be represented by the generalized Kelvin-Voigt mechanical model. It is well known that an exhaustive study of colloidal dispersions may require the determination of its viscoelastic properties over a wide frequency scale. Unfortunately, due to microstructure changes, the experiments are limited in time. In order to avoid such limitation, oscillatory data were deduced from creep curves - without actually vibrating the clay dispersions - because a periodic experiment at frequency w is qualitatively equivalent to a creep test at time 1/w. That is, it was possible to complete the dynamic response in the low-frequency range using data obtained from the transient response in creep.

Abstract: In spite of the geological knowledge accumulated on more than 800 uninterruptedly cored wells during the forty last years, the drilling of the 8" 112 diameter phase of Hassi-Messaoud oil field (Algeria) remains delicate because of excavation and drilling mud losses problems. The main objective of this work was to study the problem of drilling mud losses by the use of a sedimentological approach and to localize the producing levels of the subjacent Cambrian. For that purpose, the fast and slow drilling advance zones in the Triassic sedimentary sequences were localized in order to establish distribution maps. Thus, it was highlighted: - that the fast advance zones correspond to the sectors without mud losses (argillaceous facies of the flood plain), whereas the zones with slow advance correspond to the significant mud losses sectors (sandy facies of the fluviatile bars); - that under the fast advance of the Triassic series, potential hydrocarbon reservoirs are located.

Abstract: With stress controlled rheometer we investigate the behavior for different concentrations, of paraffin oil-in-water emulsions, bentonite suspensions as well as charged bentonite emulsions. We were particularly interested in how aging affects the rheological properties. Using a structural model, we correlate the macroscopic experimental results to the fluid microstructure characteristic parameters and we calculate the emulsions and suspensions mean characteristic unit size. The comparison of these mean particle diameters with those obtained by microscopy and light-scattering measurements confirms the soundness of such procedure to estimate the structural characteristics, the effective concentrations and the effective mean particle diameter of oil-in-water emulsions and bentonite suspensions.

Abstract: Foams have been prepared from water added with a surfactant (Sodium-Dodecyl-Sulfate, SDS) and a polymer (Poly-Ethylene-Oxide, PEO) at different concentrations. This work was devoted to a study of the flow properties of the foams. The pressure drops were measured during flow in capillary tubes (2.5, 3.5 and 4 mm) in laminar regime. It was found a strong dependence of the flow curves on capillary diameter showing that pronounced wall slip effects exist. Two known approaches were applied to quantify the slip velocity: (a) the Mooney method, in which the key assumption is that the slip velocity depends only on the wall shear stress, was not applicable and (b) the Oldroyd-Jastrzebski method, in which the assumption is that the slip velocity depends not only on the wall shear stress but also on the flow geometry, yielded satisfactory results. The determination of the pressure drop coefficient showed that the Metzner and Reed correlation, i.e., the Reynolds analogy based on the generalised Reynolds number, could be applied if the data are corrected for slip effects.

Abstract: Foams have been prepared from water added with a surfactant and a polymer. A controlled stress rheometer was used to study the changes of their rheological properties during ageing by the mean of different rheological tests: shear viscosity measurements, creep compliance tests at a constant low shear stress and dynamic experiments have been performed. It has been observed that apparent viscosity decreases with ageing. A thixotropic behaviour was also found, loading and unloading curves present an hysteresis. Then, the choice of the stress ascent time is of primary importance to study the time-dependent properties of the foam. The viscosity was found to decrease with the stress ascent time while the thixotropic area decreases. Creep flow and harmonic tests have shown important viscoelastic properties of the foams. The second part of this work is concerned with the study of the flow properties of the foams. Pressure drops were measured during flow in capillary tubes in laminar regime. Pronounced wall slip effects were found. While the Mooney method for slip correction is not applicable, the Oldroyd� Jastrzebski method leads to satisfactory results. The Metzner and Reed correlation method was found to be applicable in the case of the corrected data.

Abstract: Nous nous intéressons dans cet article à la modélisation du comportement rhéologique d'une solution de polymère type ainsi qu'au changement de régime défini par deux concentrations critiques : la concentration d�enchevêtrement, c* et la concentration de transition vers le régime concentré, c**. Le présent article complète un travail antérieur [1] dans lequel une série de mesures rhéologiques, en écoulement de cisaillement, en régime transitoire (fluage) et en régime dynamique (oscillations), a été réalisée sur des solutions aqueuses de carboxymethylcellulose, CMC, à différentes concentrations. On a montré, dans [1], que le modèle de Cross reproduit de manière satisfaisante le comportement rhéologique des solutions et permet la détermination des deux concentrations critiques c* et c**. De même, nous avons montré ici que le modèle de Benchabane, appliqué initialement à des mélanges "eau-argile-polymère" [2], reproduit de manière plus précise le comportement rhéologique des solutions étudiées. Nous avons également montré que l'analyse des paramètres de ce modèle a permis d�une part, de le valider sur les solutions de CMC et d�autre part, de confirmer l'aspect physique de ses paramètres, notamment la viscosité à 1s-1, η1, ce qui facilite la détermination des concentrations critiques c* et c**, les mêmes que celles obtenues par l�application du modèle de Cross.

Abstract:

Abstract: The goal of the present work is to investigate the effect of a non-ionic polymer, generally used in the formulation of drilling fluids, on the rheological behavior of bentonite suspensions. Rheological, granulometric and zetametric measurements were carried out on a bentonite suspension, PEO solutions (polyethylene oxide, molecular weight of 4.106, 4.105 et 105 g/mol) and bentonite-PEO mixtures at different PEO concentrations. The study revealed a strong increase of the viscosity, the yield stress and the viscoelastic properties of the bentonite suspension. The origin of this rheological behavior change was discussed on the basis of the zetametric and granulometric results and could be explained by the bridge network ensured by the polymer chains between the bentonite particles.

Abstract: The study of two-phase flow, such as liquid-solid suspensions, requires the development of adequate experimental tools. They must allow the determination of both velocity distributions for the two species mixed together. It has been demonstrated that the use of ultrasound velocimetry for two-phase flow is able to characterise the dynamic properties of the transported particles. Then, the sliding velocities can be investigated. A significant change of the velocity profile, due to the presence of the solid phase can be observed. However, the direct interpretation of the measurements appears very difficult. The study of the velocity histograms allows us to determine both fluid and solid particles velocities. We interpret the first of the two peaks as the fluid particle velocity and the second peak as the suspension velocity.

Abstract: In this study, we explain by granulometric measurements, the addition of an anionic polymer effect (Carboxy Methyl Cellulose of sodium: CMC) on the rheological behavior of the bentonite suspensions. It was shown that for destructurated suspensions and independently of the CMC molecular mass, this last causes an increase of the number of small particles. The mechanical history is responsible for the destruction of the suspensions, the CMC being used only to coat the particles and to prevent their agglomeration; in this case, the mechanism of destructuration-reorganization depends on the polymer.

Abstract: The aim of our research project is to create magnetic forces on a flow of bentonite suspensions in order to get a rheological characterization of the fluid. The magnetic forces, linked to the gradient of the square magnetic induction, must be sufficient to modify the radial speed profile of the flow. Bentonite suspensions are non-Newtonian fluids which have unique rheological properties. Relatively small quantities of bentonite suspended in water form a viscous, shear thinning gel. Moreover, bentonite suspensions are thixotropic, exhibiting a stable form at rest but becoming fluid when agitated. Much of bentonite`s usefulness is in the drilling and geotechnical engineering industry and the cosmetic industry. The crucial issue of the study is to obtain a high magnetic field and a non-uniform gradient (contrary to magnetic levitation). We intend to develop a system based on one or more superconducting coils. We present the optimal configuration of the superconducting system required to obtain the maximum of gradient of the square magnetic induction and a non-uniform gradient in the working area. We performed numerical investigations with different configurations: a multi-coil one and another one with a comparison of different shape of coils. We managed to calculate the modification of the speed profile for a water flow. The results show the feasibility of this project of great interest for the rheological characterization of complex fluids.

Abstract: Nous nous intéressons dans cet article à la modélisation du comportement rhéologique d'une solution de polymère type ainsi qu'au changement de régime défini par deux concentrations critiques : la concentration d�enchevêtrement, c* et la concentration de transition vers le régime concentré, c**. Le présent article complète un travail antérieur [1] dans lequel une série de mesures rhéologiques, en écoulement de cisaillement, en régime transitoire (fluage) et en régime dynamique (oscillations), a été réalisée sur des solutions aqueuses de carboxymethylcellulose, CMC, à différentes concentrations. On a montré, dans [1], que le modèle de Cross reproduit de manière satisfaisante le comportement rhéologique des solutions et permet la détermination des deux concentrations critiques c* et c**. De même, nous avons montré ici que le modèle de Benchabane, appliqué initialement à des mélanges "eau-argile-polymère" [2], reproduit de manière plus précise le comportement rhéologique des solutions étudiées. Nous avons également montré que l'analyse des paramètres de ce modèle a permis d�une part, de le valider sur les solutions de CMC et d�autre part, de confirmer l'aspect physique de ses paramètres, notamment la viscosité à 1s-1, h1, ce qui facilite la détermination des concentrations critiques c* et c**, les mêmes que celles obtenues par l�application du modèle de Cross.

Abstract: