Page 96 - Petrophysics
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PROPERTIES OF SUBSURFACE FLUIDS 69
Figure 2.17. Viscosity of gases at one atmosphere as a function of temperature (301.
The "API gravity does not have a linear relationship to the physical
properties of petroleum or its fractions; therefore, it is not a measure
of the quality of petroleum. The measurements are important, however,
because the "MI gravity is used with other parameters for correlation of
physical properties. Also, the price of petroleum is commonly based on
its API gravity.
A comparison of API gravity and specific gravity is shown in Table 2.6.
Specific gravity (SG) is the density of the fluid at any temperature
and pressure divided by the density of water at GOOF and 14.7 psia
(62.34 lbm/ft3; where lbm = pounds mass). Note that the API gravity
is inversely proportional to the specific gravity and an OAPI gravity of 10
degrees corresponds to the specific gravity of water at GOOF (SG = 1 .O).
Oil Viscosity
Two methods for measuring the viscosity of crude oils and their
fractions that have received universal acceptance are: (1) the kine-
matic viscosity measurement, which is obtained by timing the flow of
