Foams rheology

Foam rheology has been a challenging area of research of interest for the yield behavior and stick-slip flow behavior (see the review by Kraynik [229]). Recent studies by Durian and co-workers combine simulations [230] and a dynamic light scattering technique suited to turbid systems [231], diffusing wave spectroscopy (DWS), to characterize coarsening and shear-induced rearrangements in foams. The dynamics follow stick-slip behavior similar to that found in earthquake faults and friction (see Section XU-2D). 

Foam-injection molding Foam plastic sheathing Foam products Foam regulators Foam rheology... 

The behavior of foam in porous media has been the subject of entensive study and recently a collection of papers on this subject (369), a review of foam rheology (370), and an extensive bibliogra-phy (371) have been published. X-ray computerized tomographic analysis of core floods indicated that addition of 500 ppm of an alcohol ethoxyglycerylsulfonate increased volumetric sweep efficiency substantially over that obtained in a WAG process (364). 

Figure J.. Schematic representation of the flow diagram of the foam rheology rig.

Heller J.P. and Kuntamukkula M.S. "Critical Review of Foam Rheology Literature" 1nd.Eng.Chem. 1987 26 318,... 

In a later study [56], the effect of gas volume fraction (foam rheology was investigated. Two models were considered one in which the liquid was confined to the Plateau borders, with thin films of negligible thickness and the second, which involves a finite (strain-dependent) film thickness. For small deformations, no differences were observed in the stress/strain results for the two cases. This was attributed to the film thickness being very much smaller than the cell size. Thus, it was possible to neglect the effect of finite film thickness on stress/strain behaviour, for small strains. 

Foam products Foam regulators Foam rheology... 

While the Bingham plastic model is an adequate approximate description of foam rheology, it is by no means exact, especially at low strain rates. More detailed models attempl to relate the rheological properties of foams to the structure and behavior of the bubbles. 

The critical analysis of the results on foam rheology, proposed by Heller and Kuntamukkula [16], has shown that in most of the experiments the structural viscosity depends on the geometrical parameters of the device used to study foam flow. This means that incorrect data about flow regime and boundary conditions, created at the tube and capillary walls, etc., are introduced in the calculation of viscosity (slip or zero flow rate). Most unclear remains the problem of the effect of the kind of surfactant and its surface properties on foam viscosity and on the regime of foam flow (cross section rate profile and condition of inhibition of motion at the wall surface). 

A critical literature review on foam rheology is given elsewhere (6). The injection of foam-like dispersions or C02 foams is a useful method in enhanced oil recovery ( 7). This method of decreasing the mobility of a low-viscosity fluid in a porous rock requires the use of a surfactant to stabilize a population of bubble films or lamellae within the porespace of the rock (8). The degree of thickening achieved apparently depends to some extent on the properties of the rock itself. These properties probably include both the distance scale of the pore space and the wettability, and so can be expected to differ from reservoir to reservoir, as well as to some extent within a given field (9,10). 

It is difficult to study the rheological properties of a foam since, on deformation, its properties are changed. The most convenient geometry to measure foam rheology is to use a parallel plate. The rheological properties could be characterised by a variable viscosity [4],... 

Prud home, R.K. and Khan, S.A., Experimental results on foam rheology, in Eoams Theory, Measurements, and Applications, Prud home, R.K. and Khan, S.A., Eds., Marcel Dekker, New York, 1996, p. 217. 

Khan, S. A., Foam rheology Relation between extensional and shear deformations in high gas fraction foams, Rheological Acta, Vol. 26, No. 1, pp. 78-84, 1987. 

Two important parameters that describe a foam are texture and stability. Although both are dominant factors in the determination of foam rheology, neither is stipulated but is assumed when designing a foam fluid treatment. 

Systematic studies of the foam rheology [932-939] show that the power-law index varies between 0.25 and 0.5 depending on the elasticity of the individual air-solution surfaces. If the elasticity is lower than 10 mN/m, then n is close to 0.25, whereas for large surface elasticity (>100 mN/m) n increases to 0.5. 

Denkov, N.D., Tcholakova, S., Fldhler, R., and Cohen-Addad, S., Foam rheology, in Foam Engineering Fundamentals and Applications, Stevenson, P. (Ed.), John WUey Sons, Chichester, U.K., 2012, p. 91. 

Foams that are relatively stable on experimentally accessible time scales can be considered a form of matter but defy classification as either solid, liquid, or vapor. They are solid-like in being able to support shear elastically they are liquid-like in being able to flow and deform into arbitrary shapes and they are vapor-like in being highly compressible. The rheology of foams is thus both complex and unique, and makes possible a variety of important applications. Many features of foam rheology can be understood in terms of its microscopic structure and its response to macroscopically imposed forces. 

Foam rheological behavior is somewhat like that of the polymers described earlier in that they also are pseudoplastic. However, the foam flow is more complex and is dependent on a larger number of variables, as discussed. 

Another approach to describing foam rheology has been to calculate an apparent foam viscosity from flow-rate and pressure-drop measurements made during flow through a porous medium, Darcy s law is used with the rock permeability, or water relative permeability if an oil phase is present, to calculate apparent foam viscosity. Results show that the apparent viscosity calculated in this manner is a strong function of foam quality, decreasing approximately linearly as foam quality increases. Ifiis approach essentially treats the foam as a single phase. 

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