residual saturation based on drainage–imbibition experiment curves (Bear 1972;
Dullien 1992; Fetter 1994; Freeze and McWhorter 1997; Pickell et al. 1966).
Figure 2.9 is an example of a drainage–imbibition curve.
A drainage–imbibition experiment showed that when the capillary pressure is
increased (. c ¼ . nw À . w ) drainage occurs, and water saturation begins to decrease
(from 100%). Water saturation continues to decrease until no more water can exit the
porous medium system; the water left in the medium is called irreducible water
saturation (S rw, or residual saturation of water). Conversely, if the capillary pressure
is decreased, imbibition occurs and DNAPL saturation decreases [from (1À S rw )].
By reducing the capillary pressure, DNAPL saturation continues to decrease until it
reaches a point when no more DNAPL can exit the system. This DNAPL concentration in the system is called residual saturation of DNAPL (S rnw ). The threshold
pressure is the minimum force required to overcome the resistance of the capillary
pressure (entry pressure) of a porous medium.
Retention Models . r -. w and . c -. w
Many researchers have used empirical relationships and experimental data fitting by
mathematical functions to obtain . c -. w and . r -. w curves (e.g., van Genuchten 1980;
Brooks and Corey 1964). Numerical models generally use a van Genuchten-based
(VG) or a Brooks–Corey-based (BC) constitutive model. These constitutive models
are integrated with extensions of the relative permeability functions proposed by
either Burdine (1953) or Mualem (1976). In reservoir engineering, a commonly used
expression is the Brooks–Corey and Burdine equation. Aquifer treatment and
remediation also use van Genuchten–Mualem equation. Brooks–Corey–Mualem,
van Genuchten–Burdine, and van Genuchten–Mualem equations have been used
successfully (O’Carroll et al. 2004).
Fig. 2.9 Drainage–imbibition curves [adapted from Benremita (2002)]
72
S. Colombano et al.
Dullien 1992; Fetter 1994; Freeze and McWhorter 1997; Pickell et al. 1966).
Figure 2.9 is an example of a drainage–imbibition curve.
A drainage–imbibition experiment showed that when the capillary pressure is
increased (. c ¼ . nw À . w ) drainage occurs, and water saturation begins to decrease
(from 100%). Water saturation continues to decrease until no more water can exit the
porous medium system; the water left in the medium is called irreducible water
saturation (S rw, or residual saturation of water). Conversely, if the capillary pressure
is decreased, imbibition occurs and DNAPL saturation decreases [from (1À S rw )].
By reducing the capillary pressure, DNAPL saturation continues to decrease until it
reaches a point when no more DNAPL can exit the system. This DNAPL concentration in the system is called residual saturation of DNAPL (S rnw ). The threshold
pressure is the minimum force required to overcome the resistance of the capillary
pressure (entry pressure) of a porous medium.
Retention Models . r -. w and . c -. w
Many researchers have used empirical relationships and experimental data fitting by
mathematical functions to obtain . c -. w and . r -. w curves (e.g., van Genuchten 1980;
Brooks and Corey 1964). Numerical models generally use a van Genuchten-based
(VG) or a Brooks–Corey-based (BC) constitutive model. These constitutive models
are integrated with extensions of the relative permeability functions proposed by
either Burdine (1953) or Mualem (1976). In reservoir engineering, a commonly used
expression is the Brooks–Corey and Burdine equation. Aquifer treatment and
remediation also use van Genuchten–Mualem equation. Brooks–Corey–Mualem,
van Genuchten–Burdine, and van Genuchten–Mualem equations have been used
successfully (O’Carroll et al. 2004).
Fig. 2.9 Drainage–imbibition curves [adapted from Benremita (2002)]
72
S. Colombano et al.