Page 67 - Introduction to Petroleum Engineering

DEFINITIONS 51
The dissolved gas–oil ratio is the volume of dissolved gas measured in standard
cubic feet (SCF) to the volume of oil measured in stock tank barrels (STB) as
obtained from surface separation equipment. The oil FVF is the corresponding
volume of oil at reservoir conditions (RB for reservoir barrels) of temperature and
pressure divided by the stock tank volume of oil (STB). As fluids flow from the
reservoir to the surface separator and stock tank, pressure and temperature decrease.
In response to decreasing pressure, gases bubble out of the oil phase, and the oil
volume decreases. Stock tank gravity is a measure of specific gravity. In Table 3.2,
it is reported in °API. The relation of °API to specific gravity is described in another
section of this chapter.

3.3 DEFINITIONS

In this section, we provide brief definitions and units for many of the fluid prop-
erties encountered in the oil and gas industry. Unit conversion factors are found in
Appendix A. In subsequent sections, we include examples of correlations for the
fluid properties most often needed by petroleum engineers.
Pressure. Fluid properties depend on pressure, temperature, and composition.
Pressure is defined as normal force divided by the area to which it is applied.
2
2
Some common units of pressure include pounds/in or psi, pascals (Newtons/m ),
atmospheres, and bars.
Temperature. Temperature is a measure of the average kinetic energy of a system.
The most commonly used temperature scales are the Fahrenheit and Celsius scales.
The relationship between these scales is

5
T = ( T − ) (3.1)
32
C 9 F
where T and T are temperatures in degrees Celsius and degrees Fahrenheit,
F
C
respectively.
Some applications, such as equations of state, require the use of absolute temper-
ature expressed in Kelvin or Rankine degrees. The absolute temperature scale in
degrees Kelvin is related to the Celsius scale by

T = T + 273 (3.2)
K
C
where T is temperature in degrees Kelvin. The absolute temperature scale in degrees
K
Rankine is related to the Fahrenheit scale by

T = T + 460 (3.3)
R
F
where T is temperature in degrees Rankine.
R