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

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

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

Rotation de Quincke dans des suspensions

La rotation de Quincke est la mise en rotation spontanée d un objet isolant immergé dans un fluide faiblement conducteur et soumis à un champ électrique continu suffisamment intense. Nous nous intéressons aux effets de cette électrorotation sur les propriétés électriques et mécaniques de suspensions de particules isolantes de Polyméthyl méthacrylate (PMMA) de 6 à 200 micromètres de diamètre. Le fluide suspendant est réalisé à partir d huiles diélectriques minérales ou organiques rendues légèrement conductrices (conductivité voisine de 10-8 S/m) par l ajout de surfactants (dodécyl benzène sulfonate ou AOT ). Nous montrons au travers d un modèle de conduction et de résultats expérimentaux que la rotation de Quincke est responsable d une augmentation de la conductivité électrique apparente des suspensions. Nous mettons d autre part en évidence théoriquement et expérimentalement un fort effet électro-rhéologique négatif : sous champ électrique des diminutions de viscosité de près d un ordre de grandeur sont mesurées en géométrie de Couette cylindrique. Une augmentation de débit en rapport est obtenue pour un écoulement de la suspension dans un canal rectangulaire de 1mm d épaisseur. Ce dernier effet existe aussi, plus modeste, dans un canal de 200 micromètres d épaisseur démontrant la possibilité d utiliser la rotation de Quincke aux échelles de la microfluidique. Diverses observations rapportées (structuration en bandes, décomposition en une phase riche et une phase pauvre en particules, ) et discutées comme autant de sources d écart à la théorie ou de pistes pour de nouvelles études (structures en chevrons, écoulements auto-entretenus).Quincke rotation is the spontaneous rotation of an insulating object immersed in a slightly conducting fluid and subjected to a high enough DC electric field. We are interested in this electroration seffects on electrical and mechanical properties of suspensions of insulating particles of Polyméthyl méthacrylate (PMMA) with a diameter form 6 to 200 microns. The suspending fluid is made of dielectric mineral or organic oils made weakly conductive (conductivity around 10-8 S/m) adding surfactants (dodécyl benzène sulfonate sait AOT). We show through a conduction model and experimental results that Quicke rotation is responsible for an increase of the apparent electrical conductivity of the suspensions. We also put in evidence theoretically and experimentally a strong negative electrorheological effect under DC electric field, viscosity decreases of about an order of magnitude is measured in a cylindrical Couette geometry. An increase of the flow rate of the same order is obtained for the suspension flowing in a rectangular cross section channel of one millimetre in thickness. This last effect also exists, more modest in a channel of 200 micrometers in thickness demonstrating the possible use of Quincke rotation on the microfluide scale. Various observations are reported (stripes structuration, decomposition into one phase with a high density and one phase with a low density of particles, ) and discussed as many origins for discrepancies between experiment and theory or ways for new studies (quincunx structures, self-maintened flows).NICE-BU Sciences (060882101) / SudocSudocFranceF

A new way to measure viscosity in droplet-based microfluidics for high throughput analysis

In this work, we propose a new way to measure viscosity of samples in a microfluidic device. By analysing the shape of droplets after an expansion, we can measure the viscosity of the phase inside the droplet knowing the surface tension between the two liquids, the flow rate, the geometry of the channel and the viscosity of the continuous phase. This work paves the road for future high throughput studies in the framework of digital microfluidics

Un exemple d'étude rhéophysique : l'électrorotation appliquée au contrôle de la viscosité d'une suspension

La rotation de Quincke décrit la mise en rotation d'objets par un champ électrique continu. Nous montrons ici comment nous avons pu abaisser la viscosité apparente d'une suspension de près d'un ordre de grandeur en la soumettant à un tel champ électrique

Microfluidic approaches for accessing thermophysical properties of fluid systems

Thermophysical properties of fluid systems are highly desirable as they are used in many industrial processes both from a chemical engineering point of view and to push forward the development of modeling approaches. To access these data, microfluidic approaches have recently attracted increasing interest as they provide flexible and reliable ways for measurements, leading to fast screening capabilities compared to conventional experimental systems. In this review, we present a general overview of microfluidic methodologies integrating in situ characterization to determine thermodynamic properties of fluid systems. In addition to drastically reducing the time to reach thermodynamic equilibria, one major advantage of microfluidics is to provide optical access to the fluid behavior, even under harsh conditions. Therefore, several in situ characterization techniques can be implemented to get insights into fluid properties. Here, we emphasize approaches developed using high pressure and high temperature microfluidics. Indeed, such conditions are of interest for energy industries and present plenty of challenges. Several recent examples of high pressure microfluidics optical approaches will be detailed, in particular to determine viscosity and density, phase equilibria, mass transfer coefficients and solubility parameters.Microfluidic Approaches mimicking BIoGeological conditions to investigate subsurface CO2 recyclin

Ultrasound internal tattooing

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Ultralow Interfacial Tension Measurement through Jetting/Dripping Transition

International audienceIn this paper, we present a dynamic microfluidic tensiometer able to perform measurements over more than four decades and which is suitable for high throughput experimentations. This tensiometer is able to withstand hard conditions such as high pressure, high temperature, high salinity, and crude oil. It is made of two coaxial capillaries in which two immiscible fluids are injected. Depending on the flow rate of each phase, either droplets or jetting will be obtained. The transition between these two regimes relies on the Rayleigh-Plateau instability. This transition can be theoretically computed thanks to a linear analysis based on the convective and absolute instabilities theory. From this model, the interfacial tension between the two phases can be calculated