Page 153 - Principles of Applied Reservoir Simulation 2E

138 Principles of Applied Reservoir Simulation

is proportional to the capillary pressure and inversely proportional to the density
difference between the two fluids (Eq. (3.7)). The height of the transition zone
is a function of saturation because capillary pressure depends on saturation. The
oil-water transition zone is typically the thickest transition zone because the
density difference between oil and water is less than the density difference
between gas and an immiscible liquid.
Figures 14-4 and 14-5 illustrate the initialization of a model containing
a nonzero capillary pressure curve. First, the height h tz above a specified contact,
such as the water-oil contact (WOC), is calculated from P c and Ap, The
saturation of a block with a mid-point at height h tz above the contact is then
calculated from the relationship between capillary pressure and saturation.

- WOC

A. Gas-Oil Transition B. Oil-Water Transition
Figure 14-4. Case 2: Include transition zone in
model.

S w = 0.20

SL, = 0.50
= 0.80 __

WOC
0.2 0.5 0.8

Figure 14-5. Initial gridblock saturations in model with transition zone.