Page 39 - Principles of Applied Reservoir Simulation 2E

24 Principles of Applied Reservoir Simulation

in the following section. Equivalent height is inversely proportional to the
difference in densities between two immiscible phases. The relatively large
density difference between gas and liquid results in a smaller transition zone
height than the relatively small difference between two liquid phase densities.

Oil-Water Capillary Pressure
Oil is the nonwetting phase in a water-wet reservoir. Capillary pressure
for an oil-water system is
p
PC,* = o - p w (3-8)
where

P 0 pressure in the oil phase [psi]
pressure in the water phase [psi]
P w
Capillary pressure increases with height above the oil-water contact (OWC) as
water saturation decreases,

Gas-Oil Capillary Pressure
In gas-oil systems, gas usually behaves as the nonwetting phase and oil
is the wetting phase. Capillary pressure between oil and gas in such a system
is
P ego = P g - P o (39}
\J.y)
where

pressure in the gas phase [psi]
P g
pressure in the oil phase [psi]
P 0
Capillary pressure increases with height above the gas-oil contact (GOC) as gas
saturation decreases.

3.3 Mobility

A measure of the ability of a fluid to move through interconnected pore
space is the concept of mobility. It is defined here for single phase and
multiphase flow. The multiphase flow definition is based on the concept of
relative permeability, which is presented next.