Stability porous media

In a given porous medium at a fixed water saturation (i.e., with P S ) set), static foam stability depends solely on the... 

The selection of a gel matrix should take into account pH and temperature stability, which should be compatible with the characteristics of the target protein. The selection of the most suitable gel should also take into account the main goal to be achieved. If the process is intended to separate proteins from low molar mass solutes (< 5 kDa), a small pore size matrix is recommended, so that proteins are completely excluded from the porous medium. Such a strategy is used for desalting samples. 

A third, related limit on the capillary pressure is created by the existence of an upper critical capillary pressure above which the life times of thin films become exceedingly short. Values of this critical capillary number were measured by Khistov and co-workers for single films and bulk foams (72). The importance of this phenomenon for dispersions in porous media was confirmed by Khatib and colleagues (41). Figure 5 shows the latter authors plot of the capillary pressures required for capillary entry by the nonwetting fluid and for lamella stability versus permeability of the porous medium. 

NaCl aqueous solution. About six pore volumes of the same solution was injected to stabilize the clay as well as to determine the absolute permeability and porosity (average permeability = 380 millidarcy, average porosity = 0.19). The porous medium was then flooded with Salem crude oil (viscosity at room temperature = 6 cp) to irreducible water content. Waterflood (1% NaCl) was carried out to waterbreak-through. The surfactant solution (3.16 x 10 mol/il,... 

The mixing of surfactant and polymer in the porous medium occurs due to both dispersion and the excluded volume effect for the flow of polymer molecules in porous media, which in turn could lead to the phase separation. Figure 16 illustrates the schematic explanation of the surfactant-polymer incompatibility and concomittant phase separation. We propose that around each micelle there is a region of solvent that is excluded to polymer molecules. However, when these micelles approach each other, there is overlapping of this excluded region. Therefore, if all micelles separate out then the excluded region diminishes due to the overlap of the shell and more solvent becomes available for the polymer molecules. This effect is very similar to the polymer depletion stabilization (55). Therefore, this is similar to osmotic effect where the polymer molecule tends to maximize the solvent for all possible configurations. ... 

Problem 12-18. Buoyancy-Driven Instability of a Fluid Layer in a Porous Medium Based on the Darcy-Brinkman Equations. A more complete model for the motion of a fluid in a porous medium is provided by the so-called Darcy Brinkman equations. In the following, we reexamine the conditions for buoyancy-driven instability when the fluid layer is heated from below. We assume that inertia effects can be neglected (this has no effect on the stability analysis as one can see by reexamining the analysis in Section H) and that the Boussinesq approximation is valid so that fluid and solid properties are assumed to be constant except for the density of the fluid. The Darcy Brinkman equations can be written in the form... 

The mosl important early work on interfacial instabilities is that of Saffman and Taylor (1958) who considered the stability of an interface between two immiscible fluids moving vertically through a porous medium. Wooding (1959,... 

Wooding, R.A. 1962b. The stability of an interface between miscible fluids in a porous medium. Z. Angew. Math. Phys. 13 255-265. 

Aqueous foams containing emulsified oils have a wide variety of practical applications. The effect of oil on foam stability is of primary importance because the oil can stabilize or destabilize the aqueous foam. Emulsification of some crude oils can lead to a decrease in foam stability, thus the application of foams for mobility control in enhanced oil recovery (EOR) is strongly affected by the foam—crude oil interactions in the porous medium. 

Schramm and Novosad (76) conducted similar studies and found that the stability of the pseudoemulsion film is an important factor in the movement of the crude oil in the porous medium. They also found that the degree of emulsification of the crude oil into the moving foam greatly afreets the oil transport. Both the degree of emulsification and the stability of the pseudoemulsion film decreased with the oil—surfactant solution interfacial tension in their systems (mostly zwitterionic surfactants) that... 

Figure 2 illustrates what is coined a discontinuous-gas foam (2, 9), in that the entire gas phase is made discontinuous by lamellae, and no gas channels are continuous over sample-spanning dimensions. Gas is encapsulated in small packets or bubbles by surfactant-stabilized aqueous films. These packets transport in a time-averaged sense through the porous medium (20). 

In a foam-laden porous medium, the capillary pressure of an equivalent undispersed two-phase system that corresponds to is termed here the critical capillary pressure for rupture. For bulk systems, is a well-documented parameter that controls the stability of the foam (77). As shown in Figure 8, even a very dilute SDS surfactant solution exhibits a critical capillary pressure for rupture greater than 100 kPa (i.e., greater than 1 atm) and creates highly robust foam films. However, not all surfactant-stabilized foam films display an inner branch. In this case, the critical capillary pressure for rupture equals IImax. 

Investigations to determine the leak-off control mechanisms of foam have shown (26—29) that the effective permeability of a porous medium is greatly reduced in the presence of foam. Some basic assumptions were used during the testing to determine the leak-off control mechanisms of foamed fracturing fluids. The first assumption was that the liquid or continuous phase moves freely, and permeability reduction is a function of the liquid saturation. The other assumption was that the gas or discontinuous phase flows only by rupture and reformation of the foam film. The resistance of foam to flow through porous media is a function of the stability of the foam. 

Schramm [257] considers it a big problem that foams are sensitive to the contact with oil under porous medium in oil recovery. While proposing a several foam breaking mechanisms under reservoir conditions, the author believes the emulsification process of oil in water is the most important step. In emulsification, the contact area of pseudo-emulsion films increases with the oil contents. In case the pseudo-emulsion films are stable, the foam stability and thus the process efficiency increases. Thinning of pseudo-emulsion films leads to its rupture when gas is continuously injected into the media, flooded with a surfactant solution at residual oil... 

Surfactants play an important role in the formation and stability of foams. Investigators have determined foam stability by measuring the half-life (e.g. t 2) the foam. Half-life is the time required to reduce foam voLume to half of its initial value. It has been demonstrated that the foam stability (i.e.half-life) decreased with increasing temperature, whereas the foaminess of the surfactant solution increased with temperature. It is likely that these properties of foam depend on the molecular structure and concentration of the surfactant at the gas/liquid interface. Comparison of the results of static foam stability with that of the dynamic behavior of foam in porous media revealed that the foam stability is not required for efficient fluid displacement or a decrease in the effective air mc >ility in a porous medium. Moreover, the ability of the surfactants to produce in-situ foam was one of the important factors in the displacement of the fluid in a porous medium. 

Avramenko, AA., Kuznetsov, AV, Basok, B.I., Blinov, D.G., 2005. Investigation of stability of a laminar flow in a parallel-plate channel filled with a fluid saturated porous medium. Phys. Fluids. 17, 094102. 

Deng, C., Martinez, D.M., 2005a. Linear stability of a Berman flowin a channel partially filled with a porous medium. Phys. Fluids 17, 024102. 

Nield, D.A., 2003. The stability of flow in a channel or duct occupied by a porous medium. Int. J. Heat Mass... 

Consolidated porous media here, the contact (cohesive) forces between elementary grains maintain the mechanical stability of the material. Usual examples of consolidated porous media include calcareous rocks, clays, vegetable, and animal tissues. The deformation or mechanical equilibrium of the porous medium is not a concern, unless its mechanical breakdown under the effect of strong forces is considered. 

Mention was made previously of the electroosmotic flow of water to the cathode encountered in electrophoresis in various stabilizing media. This phenomenon plays a relatively small role in free electrophoresis because of the small surface area in contact with the electrolyte solution in the U tube. However, it is a very familar subject to workers who deal with electrical forces in membranes and porous materials. The well-known streaming potential produced by forcing liquid under pressure through a porous medium is closely related to the electroosmotic flow. The potential of the surface to the liquid (f potential) can be determined by measurements of the volume (V) of liquid transported per second by electroosmosis, through the use of equation (1), where i denotes the current strength, k the specific... 

LINEAR STABILITY OF A PLANAR REVERSE COMBUSTION FRONT PROPAGATING THROUGH A POROUS MEDIUM GAS-SOLID COMBUSTION MODEL... 

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