Porous media displacement phenomena

The third problem is known as the Saffinan-Taylor instability of a fluid interface for motion of a pair of fluids with different viscosities in a porous medium. It is this instability that leads to the well-known and important phenomenon of viscous fingering. In this case, we first discuss Darcy s law for motion of a single-phase fluid in a porous medium, and then we discuss the instability that occurs because of the displacement of one fluid by another when there is a discontinuity in the viscosity and permeability across an interface. The analysis presented ignores surface-tension effects and is thus valid strictly for miscible displacement. ... 

In this chapter we, examine the friction term in Bernoulli s equation for flow in a porous medium as well as the phenomenon of incomplete displacement of one fluid from a porous medium by another. We also examine competitive countercurrent flow in porous media and look briefly at filtration and fluidization. 

The experiments of the second kind, that is, without simulation of the initial water saturation, were carried out at temperature of 200°C. Results recorded in Table 8 for experiment No. 7 show that, in this case, the displacement coefficient amounted to 78.3%. This value was 5.3 percentage points lower than results obtained in experiment No. 6, that is, with the simulation of water saturation. The displacement of liquids from the bed is more complete in instances when initial water saturation is simulated. This phenomenon is explained by the character of distribution of oil and water in the bed and by the surface properties of die porous medium. 

An inverse phenomenon streaming potential), generation of an electric field inside the membrane, takes place if the solution passes through this porous medium due to an imposed hydrostatic pressure. This time it is the flow of the fluid inside the pores that induces the displacement of the mobile part of the EDL at the surface of capillaries, with respect to the charges attached to the surface. These dipoles create an electric field, which, under stationary conditions, prevents the farther displacement of the mobile charges. The resulting potential difference across the membrane, A(p, is proportional to the excessive hydrostatic pressure, AP ... 

In Section 3.3.8, we observed that, in a gas-liquid-soUd system with a flat solid surface, there is either zero or a finite contact angle 9 (see Figure 3.3.16) the liquid attains this contact angle spontaneously without any other external force being present. If the contact angle is zero, the liquid spreads over the solid surface, displacing the gas/air the solid surface is said to be wetted completely by the wetting liquid. This phenomenon is routinely encountered and exploited when a porous medium, such as a porous membrane or porous bed or paper, comes into contact with a liquid which can wet the material of the porous medium. 

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