Page 27 - Principles of Applied Reservoir Simulation 2E

1.2 Principles of Applied Reservoir Simulation

where
N original oil in place [STB]
<f) reservoir porosity [fraction]
A reservoir area [acres]

h 0 net thickness of oil zone [feet]
initial reservoir oil saturation [fraction]
S oi
initial oil formation volume factor [RB/STB]
B oi
Associated gas, or gas in solution, is the product of solution gas-oil ratio R so and
original oil in place N.
Original free gas in place for a gas reservoir is given by

775844^ S .
G = ^_£. (22)
gi
where
G original free gas in place [SCF]
net thickness of gas zone [feet]
h g
Sg initial reservoir gas saturation [fraction]
initial gas formation volume factor [RB/SCF]
B gi
Equation (2.2) is often expressed in terms of initial water saturation S wi by
writing S gi = 1 - S wi. Initial water saturation is usually determined by well log
or core analysis.

2.2 Material Balance

The law of conservation of mass is the basis of material balance calcula-
tions. Material balance is an accounting of material entering or leaving a system.
The calculation treats the reservoir as a large tank of material and uses quantities
that can be measured to determine the amount of a material that cannot be
directly measured. Measurable quantities include cumulative fluid production
volumes for oil, water, and gas phases; accurate reservoir pressures; and fluid
property data from samples of produced fluids.
Material balance calculations may be used for several purposes. They