Page 310 - Principles of Applied Reservoir Simulation 2E

Part V: Technical Supplements 295

Similar definitions of transmissibility apply in all three coordinate directions.

28.3 Terminology and General Comments

Some of the fluid property terms that are most frequently used in black
oil simulation are defined here.

Density
Density is defined as the mass of a substance divided by the volume it
occupies. The density of a fluid depends on the pressure, temperature, and
composition of the fluid.

Composition
The composition of a fluid depends on whether the fluid consists of a pure
component, such as water or methane, or is a mixture. For example, petroleum
and in situ water are mixtures. Petroleum is a mixture of hydrocarbon com-
pounds, and in situ water usually contains dissolved solids, such as salt, and may
contain dissolved gases such as methane and carbon dioxide. The composition
of a fluid is a list of the components contained in the fluid.
The relative amount of each component in a mixture is defined as the
concentration of the component. Concentration may be expressed in a variety
of units, such as volume fraction, weight fraction, or molar fraction. It is
important to know the units associated with the composition. If the concentration
units are not clearly expressed in a fluid report, they should be determined before
use in calculations. It is common to find composition expressed in mole
fractions. The symbols {*„>>„ z t} are often used to denote the mole fraction of
component i in the oil phase, gas phase, and wellstream respectively.
The equilibrium K value is a measure of the amount of component i in
the gas phase relative to the oil phase. It is defined as the ratio
K, = y./x t
If component i exists entirely in the oil phase, then^, is 0 and K { is 0. Conversely,
approaches
if component i exists entirely in the gas phase, then x t is 0 and K f
infinity. Thus, the equilibrium K value for component / may range from 0 to