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

Rheology of Aqueous Foams: a Literature Review of Some Experimental Works

International audienceFoam is a dispersed system and is unstable by nature, its rheological characterization is very difficult. Numerous parameters have to be considered and controlled: foam quality, i. e. gas volume fraction, foam texture (bubbles size distribution), size of the measurement apparatus compared to bubbles size, influence of foam production method, wall slip phenomena and foam compressibility. Foam must be stable and must not evolve during measurement time. These numerous parameters do explain there is no general view concerning the behavior of this kind of system. Influence of pressure and temperature has not been the subject of many studies, even on static foam. A rigorous experimental method should consider and control each of these parameters affecting foam stability and structure

Rheology of Aqueous Foams: a Literature Review of Some Experimental Works

Foam is a dispersed system and is unstable by nature, its rheological characterization is very difficult. Numerous parameters have to be considered and controlled: foam quality, i. e. gas volume fraction, foam texture (bubbles size distribution), size of the measurement apparatus compared to bubbles size, influence of foam production method, wall slip phenomena and foam compressibility. Foam must be stable and must not evolve during measurement time. These numerous parameters do explain there is no general view concerning the behavior of this kind of system. Influence of pressure and temperature has not been the subject of many studies, even on static foam. A rigorous experimental method should consider and control each of these parameters affecting foam stability and structure

Additifs réducteurs de perte de charge en écoulement

Les additifs dits réducteurs de perte de charge les plus courants sont des solutions diluées de polymères, mais il existe d'autres types d'additifs, comme des particules solides (fibres) ou des tensioactifs (sous forme de micelles cylindriques). Ces additifs en concentration infinitésimale agissent en régime turbulent et peuvent diminuer les pertes de charge en écoulement jusqu'à 80 % par rapport au solvant pur. Leur mécanisme d'action n'est pas clairement établi, mais c'est en interagissant avec la structure de la turbulence que ces additifs vont réduire la dissipation d'énergie et donc les pertes de charge. Entre deux régimes limites - un régime sans drag reducers et le régime asymptotique où la réduction de frottement est maximale - existe un régime intermédiaire où la réduction de frottement va dépendre des caractéristiques de l'écoulement et du type d'additif. Ce régime est caractérisé par l'apparition d'une couche intermédiaire élastique entre la couche visqueuse pariétale et le noyau turbulent de l'écoulement. Des comportements différents peuvent être observés suivant la conformation des additifs macromoléculaires. L'extension des molécules en pelotes, et/ou l'alignement des polymères étendus (ou des autres additifs anisotropes) dans l'écoulement sont caractéristiques de ce phénomène de réduction de frottement

Lubrication Process at the Wall in Foam Flow Application to Pressure Drop Estimation While Drilling UBD Wells

Abstract When drilling underbalanced, the pressure of the drilling fluid is maintained at a value below the formation pressure. In order to lower the well pressure, specific low density fluids are needed, i.e., gas, aerated mud or foam. Foam is particularly beneficial for drilling mainly due to its low density coupled with good carrying capability, but its use remains hazardous due to the incomplete knowledge of its bottomhole properties, and especially of its flowing properties. Pressure drop estimation is crucial for underbalanced drilling (UBD) operations in order to be able to keep the bottom hole pressure in the adequate range in real time. In this study, we analyze the pressure drop variation with the flow rate in a circular pipe for different foam qualities and formulations. Experimental investigations are realized in a pressure and temperature circular conduct flow. We show that lubrication at the wall plays a crucial role. Indeed, the intrinsic viscosity of the foam can be very high, leading to the development of a water layer at the wall responsible for the lubrication of the flow. A two-phase description of the system allows for the analytical estimation of the pressure drop. The size of the lubricated layer is then deduced and its range of existence is discussed. Main parameters of its formation are also discussed. We show that this lubrication effect can be significant in pressure drop estimation for underbalanced operations. Introduction Underbalanced drilling is recognized as one of the most effective solutions to prevent formation damage, differential sticking or fluid losses. When drilling underbalanced, the pressure of the drilling fluid is maintained at a value below the formation pressure, and for this purpose, low density fluids are used. Foam, defined as a mixture of a gas phase and a foaming solution, is one of the most versatile aerated fluids. It allows very low densities from 0.2 s.g., and is one of the most efficient fluids for lifting the cuttings and cleaning the wellbore. However, it is very important when drilling underbalanced to keep the bottom hole pressure in an adequate range in real time. Indeed, foam, as other underbalanced fluids, is not designed to create a mud cake at the wall. Therefore, a short overbalanced period can lead to the deep penetration of a filtrate into the reservoir, severely reducing the expected productivity. One of the key features of a successful underbalanced operation is control of the bottom hole pressure. Wellbore hydraulic simulation is essential as well, to design the operation and for monitoring the drilling phase or evaluating changes in the drilling program(1). While pressure estimation for aerated fluids is often realized through multiphase modelling (with estimation of the different phase's velocities), it is possible to consider flowing foam as a fluid with a given rheology that varies with the pressure, temperature and quantity of gas. Predicting the bottomhole pressure while drilling with foam implies knowledge of foam rheological properties that depend on the foam density; the foam density being, itself, a function of the frictional and hydrostatic pressure. </jats:sec

Rheological Behavior of Drilling Muds, Characterization Using Mri Visualization

Drilling muds are very complex fluids used to drill oil wells; their functions are various: to carry the rock cuttings to the surface, to maintain a sufficient pressure against the rock formation, to lubricate and cool the bit. There are mainly two families of drilling muds: oil based muds (invert emulsion of brine into an oil phase with various additives) and water based muds (aqueous solutions of clays and polymers). Originally prepared from produced oil, oil based muds formulations have evolved to very complex compositions of various additives. The base oil may be of various nature, and additives are very complex: water droplets, surfactants, organophilic clays, viscosifyers, various solids and others. These additives give specific properties to the mud, particularly regarding rheological properties. Drilling muds are often described as thixotropic shear thinning fluids with a yield stress. Due to their complex composition, drilling muds exhibit an internal structure which is liable to modify according to the flowing and shear conditions, which may lead to non homogenous phenomena. It is therefore important to develop investigation techniques allowing to visualize the internal structure of the fluid in parallel to rheological measurements. In this study, we present rheological experiments coupled to magnetic resonance imaging (MRI). Using this technique, it is possible to determine the velocity profile in a viscometric flow. Conventional rheological experiments performed on two different drilling fluids formulations give similar flow curves: beyond a critical apparent shear rate there is a simple yielding behavior with an apparent plateau at low shear rates; below this critical shear rate there is a simple viscous behavior without yield stress. MRI experiments show that in fact, below this critical shear rate, no stable flow can occur and the deformation is localized in a region of the sample the dimensions of which may depend on the size of the constitutive elements. The (macroscopic) rheological behavior observed from conventional rheometric experiments is then the signature of this sheared zone and does not represent the behavior of the bulk material