Viscoelastic fracturing fluids

Acharya, A. "Particle Transport in Viscous and Viscoelastic Fracturing Fluids," SPE Prod. Eng.. March 1986, 104 110. 

A methyl quatemized erucyl amine [660] is useful for aqueous viscoelastic surfactant-based fracturing fluids in high-temperature and high-permeability formations. 

Although polymeric rheology control additives dominate the market for fracturing fluids, cationic surfactant-based systems have been introduced. Ethoxylated quaternary ammonium salts have been shown to afford viscoelastic aqueous fracturing fluids. The strength and temperature stability of the viscoelastic formulations depends upon the purity of the surfactant. These systems are claimed to break upon exposure to hydrocarbons, thereby affording clean-up behaviour superior to that available when using polymer-based fracture fluids. 

Fracturing fluid system wasconsisted of fluorocarbon surfactant AS-3, viscoelastic surfactant VES-A as a foam stabilizer, 0.5% DW clay stabilizer, and water foam. 

Foam was completely different from gel fracturing fluid. Foam fracturing fluid could not be measured as gel fracturing fluid criterion such as temperature resistance property, shear resistance property, conductivity property, etc. Other properties of foam fracturing fluid were evaluated by interior experiment. Foam fracturing fluid formulations were the mass fraction of 0.3% fluorocarbon surfactant AS-3, the mass fraction of 0.4% viscoelastic surfactant VES-A as a foam stabilizer, 0.5% DW clay stabilizer and water. 

During the extrusion of polymers different defects and flow instabilities occur at very low Reynolds numbers. The commonly known ones are sharkskin, melt fracture, slip at the wall and cork flow. These defects are of commercial importance, since they often limit the production rate in polymer processing. Many researchers have been interested in the subject, and thorough reviews on flow stability and melt fracture have been written in the last 30 years [1-4]. More recently, two review papers deahng with viscoelastic fluid mechanics and flow stability, were published by Denn [5] and Larson [6]. However, although much work has been done in the field of extrusion distortions, controversy still exists regarding the site of initiation and physical mechanisms of the instabilities. 

The possible development of gradients in the components of the interfacial stress tensor due to flow of an adjacent fluid implies that the momentum flux caused by the the flow of liquid at one side of the interface does not have to be completely transported across the interface to the second fluid but may (partly or completely) be compensated in the interface. The extent to which this is possible depends on the rheological properties of the interface. For small shear stresses the interface may behave elastically or viscoelastically. For an elastic interfacial layer the structure remains coherent the layer will only deform, while for a viscoelastic one it may or may not start to flow. The latter case has been observed for elastic networks (e.g. for proteins) that remciln intact, but inside the meshes of which liquid can flow leading to energy dissipation. At large stresses the structure may yield or fracture (collapse), leading to an increased flow. 

A key characteristic of plastic deformations is that they are irreversible. The difference between a viscoelastic fluid and a plastic material is the presence of a yield stress. The yield stress is the stress at which the deformation becomes irreversible and once the yield stress has been exceeded then the deformation is irreversible (Figs. 14 and 15). For example, brittle materials often behave elastically until the yield point has been reached once this point has been exceeded, the material will irreversibly deform or fracture like a piece of chalk (Fig. 15A). The key feature of a brittle material is that there is little deformation after the yield point. In contrast to a brittle material are a ductile materials (Fig. 15B) ductile materials undergo a lot of deformation after the yield point. 

A fluid, which although exhibits predominandy viscous flow behavior, also exhibits some elastic recovery of the deformation on release of the stress. The term viscoelastic is reserved for solids showing both elastic and viscous behavior. Most plastic systems, both melts and solutions, are viscoelastic due to the molecules becoming oriented due to the shear action of the fluid, but regaining their equilibrium randomly coiled configuration on release of the stress. Elastic effects are developed during processing such as in die swell, melt fracture, and frozen-in orientation. 

Polypropylene melts are viscoelastic fluids. As such, the melts exhibit non-Newtonian viscosity, normal stresses in shear flow, excessive entrance-and-exit pressure drop, die swell, secondary entrance flows, melt fracture, and draw resonance. (Newtonian fluids also exhibit draw resonance.) Polypropylene melts are more viscoelastic than melts of nylon and polyester. 

In recent years, the SPH methods in particular have gone through major improvements, and their application was expanded into a wider range of engineering problems. These include both more advanced physical models and more advanced engineering processes. For example, SPH was successfully used to simulate non-Newtonian fluid flows and viscoelastic materials. It has been also used for the analysis of fluid-stmcture interaction problems, fluid flow in porous media and fractures, heat transfer, and reacting flow problems. 

From the relation L=f(vij) it is obvious that the spinnability is governed by two processes, namely the cohesive break (or the swell effect) and the melt break (capillary break, melt fracture). According to Section 11.3.1, a certain amount of elastic energy can be stored in all viscoelastic fluids. This phenomenon leads, among others, to the Barus effect. 

White JL (1964) Dynamics of viscoelastic fluids, melt fracture, and the rheology of fiber spinning. J Appl Polym Sci 8 2339-2357... 

An internal mixer with a glass window was used by Shih et al. [47] to observe mixing of different polymeric compositions prepared from HDPE, PBT, and PAr. Four sequential characteristic states were identified 1. Elastic solid pellets, 2. Deformable solid pellets, 3. Transition material either 3.1 liquid with suspended solid particles, 3.2 fractured or semi-liquid material, or 3.3 dough-like material, and 4. Viscoelastic fluid. Very high... 

Basic description of non-Newtoruan fluids is provided so that concepts of shear rate dependent viscosities with or without elastic behavior, yield stress with or without shear rate dependent viscosities and time dependent viscosities at fixed shear rates get classified. The filled polymer systems fall into the category of pseudoplastic fluids with or without yield stress and also often depict the behavior of thixotropic fluids. Their viscoelasticity may give rise to various anamolous effects that are discussed in Chapter 2, such as the Weissenberg effect, extrudate swell, drawn resonance, melt fracture and so on. 

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