Environmental Engineering Reference
In-Depth Information
Figure 14.3.
Hydrocarbon reservoir in equilibrium,
macroscopic view
We now define the following expressions:
− for an oil-water system:
p
cw
= p
o
- p
w
[14.1]
− for an oil-gas system:
p
cg
= p
g
- p
o
[14.2]
− for a water-gas system:
p
c
= p
g
- p
w
[14.3]
where
p
cw
is the capillary pressure between oil and water,
p
cg
the capillary pressure
between oil and gas, and
p
c
the capillary pressure between water and gas.
p
o,w,g
are
the pressures of oil, water and gas respectively. They are valid in local
thermodynamic equilibrium conditions, which are assumed to prevail throughout the
domain of interest.
The capillary pressures are linked to the level of saturation,
S
o,w,g
respectively,
through relations of the type shown in Figure 14.4. In reality these curves show
hysteresis effects, which are not considered here.
