Retention and Transfer of Pollution by Hydrocarbons: Mechanisms and Numerical Modeling - Environmental Geomechanics - page 402

0.0

-0.4

-0.8

E = .9631E+09
E = .9631E+06
E = .9631E+05

0 200 400 600 800

Production time (days)

Figure 14.11. Effects of reservoir compaction on reservoir pressure, for three different
reservoir rocks (redrawn with permission from [LEW 98b])

14.3.5.2. Immiscible pollutant

DNAPL exist as separated fluid phases in ground water and are classified into a
single class of subsurface hazardous pollutants. With the numerical model of the
previous example it is possible to simulate a situation where such a fluid, e.g. PCB
oil, which is heavier than water, displaces water in a phreatic aquifer.

The test example involves a vertical sand column of 1 m in height, initially fully
saturated with water, with a porosity of 0.4, a bulk modulus K s = 1 x 10 12 N/m 2 ,
Young's modulus E = 1.3 x 10 6 N/m 2 and a Poisson ratio ν = 0. At time instant
t = 0, the pollutant is injected continuously at the top of the column where a fixed
saturation degree of 0.5 is maintained for the pollutant. The result is a displacement
of water from the column by the encroaching NAPL. At the bottom of the column
the water flows out with a capillary pressure equal to zero, i.e. water and
pollutant pressures are constant and equal to the reference pressure. The viscosity
of the pollutant is 0.57 x 10 -3 Ns/m 2 and its density 1,461 kg/m 3 . Water density
is 1,000 kg/m 3 and its viscosity 1.0 x 10 -3 Ns/m 2 . The following two values of
the intrinsic soil permeability have been taken into account: 1.0 x 10 -11 m 2 and
1.5 x 10 -12 m 2 . Brooks and Corey [BRO 66] functions are used to relate the capillary
and pore pressure distribution index to saturation and relative permeability. In
particular, the irreducible saturation is set to S wc = 0.086, pore size distribution index
is λ = 2.0 and bubbling pressure p b = 0.1784. The lateral surfaces are impermeable
to fluids and have fixed horizontal displacements.

The vertical and horizontal displacements are also fixed at the bottom surface.
On the top surface p w = p ref − p sw =0.5 , the air pressure p a = p ref . p sw =0.5 means the