Page 23 - Fundamentals of Enhanced Oil and Gas Recovery

An Introduction to Enhanced Oil Recovery 11

repulsive and attractive forces between molecules, are the parameters ignored in an
ideal gas relationship. Therefore a modification factor should be considered in the
basic equation to improve the prediction of fluid behavior. Gas compressibility factor,
or z-factor, is the term introduced to the basic ideal gas relationship:
PV 5 ZnRT

where the gas compressibility factor z is defined as the actual volume of n-moles of
gas at T, and p divided by the ideal volume of the same number of moles at the same
condition.

1.9.5 Gas Formation Volume Factor

The volume of gas in reservoir condition is definitely less than the volume in surface con-
dition. The term gas formation volume factor is used to relate the volumes in reservoir
and standard condition. This term is defined as the ratio of volume of certain amount of
gas in reservoir condition to the same amount of gas in standard condition, as follows:
V g
B g 5 reservoir
V g
S:C
where
B g is gas formation volume factor
is volume of gas in reservoir condition
V g
reservoir
V g is volume of gas in standard condition
S:C
1.9.6 Gas Viscosity
The viscosity of a fluid represents the resistance to flow. In the case of low viscosity,
by inserting a certain shearing force, the fluid starts to flow and a sharp velocity gradi-
ent is created between fluid layers. Viscosity is defined as the ratio of shear stress to
the velocity gradient.
Experimental methods are not common for gas viscosity measurement. Many
empirical correlations are developed for gas viscosity measurements, which are mostly
the function of pressure, temperature, and gas composition.

1.9.7 Crude Oil Properties
A complex mixture of hydrocarbonic and nonhydrocarbonic components that are liq-
uid under reservoir condition is called crude oil. The physical and chemical properties
of crude oil are mainly obtained by experimental approaches. These properties are
strongly dependent on the reservoir conditions and fluid composition. In the absence
of experimental methods, empirical correlations are used to estimate the crude oil
properties. Crude oil gravity, specific gravity of the oil, solution gas, gas solubility,