Page 312 - Principles of Applied Reservoir Simulation 2E

Part V: Technical Supplements 297

Intensive and Extensive Properties
Pressure, temperature, and density are examples of intensive properties.
An intensive property is a fluid property which is independent of the amount
of material. For example, if a cubic cell of gas in an equilibrium state is divided
into two halves by a vertical partition, the gas in each half of the cell should have
the same pressure and temperature. By contrast, the mass and volume in each
half will be one half of the original mass and volume. Mass and volume are
examples of extensive properties. An extensive property is a property that
depends on the amount of material.

Compressibility
If the surface of an object is subjected to an external force, the resulting
pressure applied to the object can change the volume of the object. Compressibil-
ity is a measure of the volume change resulting from the applied pressure. The
fractional volume change AF/Fof an object may be estimated from

V
where c is the compressibility of the object, AP is the pressure applied, and the
minus sign implies that an increase (decrease) in applied pressure results in a
decrease (increase) in the volume of the object.

Formation Volume Factor
Formation volume factor is defined as the volume occupied by a fluid
phase at reservoir conditions divided by the volume occupied by the fluid phase
at standard conditions. The fluid phase volume may change substantially as
pressure and temperature change.
Ordinarily the volume of a fluid with constant composition will increase
as the applied pressure and temperature decrease. The behavior of petroleum
is made more complex because it is a mixture and can experience a change in
composition as temperature and pressure change. For example, a barrel of oil
at reservoir conditions (relatively high pressure and temperature) will shrink as
the barrel is brought to the surface (relatively low pressure and temperature).
The shrinkage is associated with the release of solution gas as the pressure and