Normal Stresses and Interface Displacement: Influence of Viscoelasticity on Enhanced Oil Recovery Efficiency

International audienceOne of chemical Enhanced Oil Recovery (EOR) methods consists in injecting aqueous solutions of polymers into the reservoir in order to improve mobility ratio between the injected fluid and the remaining oil. This "polymer flooding" process is usually only characterized with the low shear viscosity of the injected fluid, even if these aqueous solutions are strongly shear thinning and may show high elastic properties evidenced by normal stresses appearance. In order to study the mechanisms at the interface level, we develop simple model experimentations with the goal of quantifying the influence of viscoelastic properties on fluid displacement in a simple geometry. For this purpose, we propose and characterize a model fluid formulation, for which elastic and viscous effects can be tuned systematically. We study then the displacement of a viscous oil by a Newtonian non elastic, a viscoelastic or a purely shear thinning fluid in a two dimensional flow cell. Observing the shape of the interface between aqueous fluids and displaced oil permits to appreciate viscoelasticity effects on the displacement. Using model geometries and controlled rheology fluids, we show that viscoelastic fluids tend to better displace immiscible liquids than Newtonian fluids and that those effects are closely related to the apparitions of normal stresses independently of shear thinning property or variation of interfacial tension as soon as viscous effects govern the flow

Transition from a simple yield stress fluid to a thixotropic material

From MRI rheometry we show that a pure emulsion can be turned from a simple yield stress fluid to a thixotropic material by adding a small fraction of colloidal particles. The two fluids have the same behavior in the liquid regime but the loaded emulsion exhibits a critical shear rate below which no steady flows can be observed. For a stress below the yield stress, the pure emulsion abruptly stops flowing, whereas the viscosity of the loaded emulsion continuously increases in time, which leads to an apparent flow stoppage. This phenomenon can be very well represented by a model assuming a progressive increase of the number of droplet links via colloidal particles.Comment: Published in Physical Review E. http://pre.aps.org/abstract/PRE/v76/i5/e05140

Enhanced displacement of a liquid pushed by a viscoelastic fluid.

International audienceWe consider the displacement, in a rectangular channel, of a Newtonian oil pushed by different types of liquids (Newtonian, shear-thinning, viscoelastic) of slightly higher apparent viscosity. ln the absence of viscoelastic effects the interface between the two fluids becomes sharper at larger velocities, so that the thickness of the lateral film left behind increases with the flow rate. On the contrary, with a viscoelastic fluid, the shape of the interface is almost independent of the velocity so that the thickness of the lateral film is approximately constant. Moreover this thickness decreases when the ratio of normal to tangential stresses increases, suggesting that this effect can be attributed to normal stress differences. A heuristic theoretical approach tends to confirm this statement

Efficacy of an osteopathic treatment for infants with biomechanical sucking dysfunctions

Introduction : L’allaitement maternel est recommandé par les instances nationales et internationales pour ses bénéfices sur la santé des mères et des enfants. Près de neuf mères sur dix initient l’allaitement au Québec. Pour celles qui arrêtent dans le premier mois, une sur deux met en cause des problèmes mécaniques de succion chez le bébé en dépit du support de consultantes en lactation (CL). Les ostéopathes, dans le monde entier, reçoivent ces bébés. Cependant, peu d’études scientifiques sont publiées sur la contribution de cette profession à ce sujet. L’objectif primaire de cette étude était de déterminer l’efficacité d’un traitement ostéopathique, couplé à des consultations d’allaitement usuelles, chez les nouveau-nés ayant des difficultés mécaniques de succion. Méthode : Un essai contrôlé randomisé en simple aveugle portant sur 97 dyades maman-bébé référées par des CL a été réalisé. Les dyades étaient réparties en deux groupes : intervention ostéopathique ou soins usuels. Quatre temps de mesure sur une période de 10 jours, ont permis de déterminer l’efficacité de la succion pré et post intervention, l’intensité de la douleur chez la mère ainsi que tout effets secondaires perçus. Les lésions ostéopathiques ont été colligées afin de dresser un profil. Des tests-t, des Chi-carrés ainsi que des modèles de régression ont permis l’analyse des différences entre les deux groupes à l’étude. Résultats : Les bébés ayant reçu l’intervention ostéopathique ont montré une efficacité de succion cliniquement et statistiquement supérieure au groupe de soins usuels (p<0.001). Les analyses n’ont pas montré de différence statistiquement significative entre les groupes quant à la douleur ressentie par la mère aux différents temps de mesure. Cependant, à 3 jours post intervention, les mères du groupe intervention ont perçu une diminution significative de leur douleur (p=0.001). Un profil des bébés recrutés a pu être dressé avec des dysfonctions en postérieur du crâne chez 84,5% d’entre eux. Aucun effet secondaire grave ni sévère n’a été rapporté. Conclusion : L’ostéopathie couplée à un suivi par des CL, semble une approche prometteuse pour les dyades mère-bébé ayant des difficultés mécaniques de succion. D’autres recherches seraient à prévoir pour bonifier l’intervention ostéopathique en terme de moment, de bébés pouvant profiter de ce type de suivi, et aussi la documentation des zones en lésion.Abstract: Background: National and international policies recommend breastfeeding for its benefits on mothers’ and infants’ health. In Quebec, almost nine out of ten mothers initiate breastfeeding with their baby but half of these stop during the first month, due to biomechanical sucking difficulties, and this, despite increasing support from lactation consultants (LC). Osteopaths worldwide work with these babies, but there is little empirical evidence for this type of treatment. The primary objective of this study was to determine the efficacy of an osteopathic treatment coupled with usual lactation consultations on infants’ identified as having biomechanical sucking difficulties. Methods: A single blind randomized controlled trial including 97 mother-infant dyads referred by LC. The dyads were randomized into two groups: osteopathic intervention or usual care. Four measurement times over a 10-day period (pre and post intervention) allowed for the determination of the babies’ ability to latch, the intensity of pain felt by mothers as well as any perceived side effects. Osteopathic lesions were documented in an effort to establish a profile T-tests and Chi-square tests as well as regression models were used to compare groups. Results: Babies having received the osteopathic intervention showed a clinically and statistically significant increase (p<0.001) in their ability to latch compared to the usual care group. Analyses did not show any statistically significant difference between groups with regard to the pain felt by mothers at the different measurement times. However, 3 days post intervention, the mothers in the intervention group perceived a significant decrease in their level of pain (p=0.001). A profile of osteopathic dysfunctions in these babies was generated with 84,5% of them found to have a posterior skull dysfunction. No serious or severe side effects were reported. Conclusion: Osteopathic treatment coupled with lactation consultations seem to be a promising avenue for mother-infant dyads with biomechanical sucking dysfunctions. Further research is needed to optimize osteopathic treatment in terms of targeting babies, timing and duration of interventions and also to better document and standardize areas with osteopathic lesions

Flow induced by a sphere settling in an aging yield-stress fluid

We have studied the flow induced by a macroscopic spherical particle settling in a Laponite suspension that exhibits a yield-stress, thixotropy and shear-thinning. We show that the fluid thixotropy (or aging) induces an increase with time of both the apparent yield stress and shear-thinning properties but also a breaking of the flow fore-aft symmetry predicted in Hershel-Bulkley fluids (yield-stress, shear-thinning fluids with no thixotropy). We have also varied the stress exerted by the particles on the fluid by using particles of different densities. Although the stresses exerted by the particles are of the same order of magnitude, the velocity field presents utterly different features: whereas the flow around the lighter particle shows a confinement similar to the one observed in shear-thinning fluids, the wake of the heavier particle is characterized by an upward motion of the fluid ("negative wake"), whatever the fluid's age. We compare the features of this negative wake to the one observed in viscoelastic shear-thinning fluids (polymeric or micelle solutions). Although the flows around the two particles strongly differ, their settling behaviors display no apparent difference which constitutes an intriguing result and evidences the complexity of the dependence of the drag factor on flow field

Entrance and exit effects for a viscoelastic liquid displacing a simple liquid through a contraction.

International audienceWe studied the displacement of the interface between a viscoelastic fluid pushing a simple liquid through a rectangular contraction by following the front interface deformation in time. The progressive deformation of the interface until apparent stabilization is followed, which makes it possible to identify a transient and a stationary regime. For low Weissenberg number the shape of the interface is essentially similar to that between two simple liquids. For sufficiently large Weissenberg number the shape of the interface is different: it is narrower before the entrance and wider just after the exit. The characteristics of this shape are qualitatively analogous to those of the interface between the vortices and the convected regions for the flow of a single viscoelastic fluid through a contraction- expansion. This suggests that the entrance effect is due to extensional effects and the exit effect is due to normal stress effects