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2/26 PETROLEUM PRODUCTION ENGINEERING FUNDAMENTALS
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where the unit of formation volume factor is ft =scf. If dempsey, j.r. Computer routine treats gas viscosity as a
expressed in rb/scf, it takes the form variable. Oil Gas J. Aug. 16, 1965:141.
zT glaso, o. Generalized pressure-volume-temperature cor-
B g ¼ 0:00504 : (2:63)
p relations. J. Petroleum Technol. May 1985:785–795.
hall, k.r. and yarborough, l. A new equation of state
Gas formation volume factor is frequently used in math-
ematical modeling of gas well inflow performance relation- for Z-factor calculations. Oil Gas J. June 18, 1973:82.
ship (IPR). khan, s.a. Viscosity correlations for Saudi Arabian crude
Another way to express this parameter is to use gas oils. Presented at the 50th Middle East Conference and
3
expansion factor defined, in scf=ft ,as Exhibition held 7–10 March 1987, in Manama, Bah-
1 P rain. Paper SPE 15720.
E ¼ ¼ 35:3 (2:64) lee, a.l., gonzalez, m.h., and eakin, b.e. The viscosity of
B g ZT
natural gases. J. Petroleum Technol. Aug. 1966:997–
or 1000.
p
E ¼ 198:32 , (2:65) standing, m.b. Volume and Phase Behavior of Oil Field
zT Hydrocarbon Systems, 9th edition. Dallas: Society of
in scf/rb. It is normally used for estimating gas reserves. Petroleum Engineers, 1981.
standing, m.b. and katz, d.l. Density of natural gases.
Trans. AIME 1954;146:140–149.
2.3.7 Gas Compressibility wichert, e. and aziz, k. Calculate Zs for sour gases.
Gas compressibility is defined as Hydrocarbon Processing 1972;51(May):119.

1 @V
c g ¼ : (2:66)
V @p T Problems
Because the gas law for real gas gives V ¼ nzRT , 2.1 Estimate the density of a 25-API gravity dead oil at
p 100 8F.
@V 1 @z z
¼ nRT : (2:67) 2.2 The solution gas–oil ratio of a crude oil is 800 scf/stb
@p p @p p 2 at 3,000 psia and 120 8F. Given the following PVT
Substituting Eq. (2.67) into Eq. (2.66) yields data:
1 1 @z Bubble-point pressure: 2,500 psia
c g ¼ : (2:68) Oil gravity: 35 8API
p z @p
Gas-specific gravity: 0.77 (air ¼ 1),
Since the second term in the right-hand side is usually
small, gas compressibility is approximately equal to the estimate densities and viscosities of the crude oil at
reciprocal of pressure. 120 8F, 2,500 psia, and 3,000 psia.
2.3 For the gas composition given below, determine
apparent molecular weight, specific gravity, pseudo-
Summary critical pressure, and pseudo-critical temperature of
the gas:
This chapter presented definitions and properties of crude
oil and natural gas. It also provided a few empirical cor-
relations for determining the value of these properties. Component Mole Fraction
These correlations are coded in spreadsheet programs
that are available with this book. Applications of these C 1 0.765
fluid properties are found in the later chapters. C 2 0.073
C 3 0.021
i-C 4 0.006
References n-C 4 0.002
i-C 5 0.003
ahmed, t. Hydrocarbon Phase Behavior. Houston: Gulf 0.008
n-C 5
Publishing Company, 1989. C 6 0.001
American Petroleum Institute: ‘‘Bulletin on Performance C 7þ 0.001
Properties of Casing, Tubing, and Drill Pipe,’’ 20th N 2 0.060
edition. Washington, DC: American Petroleum Insti- CO 2 0.040
tute. API Bulletin 5C2, May 31, 1987. H 2 S 0.020
beal, c. The viscosity of air, water, natural gas, crude oils
and its associated gases at oil field temperatures and 2.4 Estimate gas viscosities of a 0.70-specific gravity gas at
pressures. Trans. AIME 1946;165:94–112. 200 8F and 100 psia, 1,000 psia, 5,000 psia, and
beggs, h.d. and robinson, J.R. Estimating the viscosity of 10,000 psia.
crude oil systems. J. Petroleum Technol. Sep. 2.5 Calculate gas compressibility factors and densities of a
1975:1140–1141. 0.65-specific gravity gas at 150 8F and 50 psia,
brill, j.p. and beggs, h.d. Two-phase flow in pipes. 500 psia, and 5,000 psia with the Hall–Yarborough
INTERCOMP Course, The Hague, 1974. method. Compare the results with that given by the
Brill and Beggs correlation. What is your conclusion?
carr, n.l., kobayashi, r., and burrows, d.b. Viscosity of 2.6 For a 0.65-specific gravity gas at 250 8F, calculate and
hydrocarbon gases under pressure. Trans. AIME plot pseudo-pressures in a pressure range from 14.7
1954;201:264–272. and 8,000 psia. Under what condition is the pseudo-
dean, d.e. and stiel, l.i. The viscosity of non-polar gas pressure linearly proportional to pressure?
mixtures at moderate and high pressures. AIChE 2.7 Estimate the density of a 0.8-specific gravity dead oil
J. 1958;4:430–436. at 40 8C.