Irreducible wetting-phase saturations

Seal properties Rock seal properties are usually described in terms of their capillary pressure characteristics, primarily wettability, entry and displacement pressures, and irreducible wetting phase saturation. Wettability defines which fluids will preferentially occupy the smallest rock pores. Entry pressure is the capillary pressure at which the non-wetting phase first displaces the wetting phase, while displacement pressure is the capillary pressure at which the non-wetting phase first forms a continuous network within the pore structure. The irreducible wetting phase saturation describes the initial connate fluid saturation at the top of the capillary column. 

Figure 5. Irreducible wetting-phase saturations for packings of spheres of various sizes and materials fall between the predicted endpoints for the intermediate (W phase trapped as pendular rings at grain contacts) and "poor levels of connectivity (W phase trapped as pendular rings and lenses in pore throats). Packings of non-spherical grains exhibit somewhat larger irreducible saturations. Data taken from Morrow (24).

Morrow, N., Irreducible wetting-phase saturations in porous media, Chemical Engineering Science 25, 1799-1818 (1970). 

SwR irreducible saturation ratio of the wetting phase, dimensionless t time, dimensional... 

Based on the geometrical model of tracheids proposed by Comstock (1970), Spolek and Plumb (1980) derived an expression for the relative permeability in softwoods. This model assumes that all tracheids are exactly similar and that the wetting-phase distribution is ideal. Their final expression involves an irreducible saturation, below which no liquid flux is possible. 

FIGURE 2.33 Relative permeability for water (wetting phase) and oil (non-wetting phase) as a function of water saturation S . The dotted vertical lines indicate the irreducible water saturation... 

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