Page 46 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

34 Reservoir Engineering

are applicable to a wider range of oil properties. The empirical correlations,
presented as a function of gas specific gravity, oil API gravity, reservoir
temperature, and pressure, are particularly convenient to use with hand-held
calculators. Gas gravity was found to be a strong correlating parameter. Since
gas gravity depends on es-oil separation conditions, Vazquez and Beggs chose
100 psig as a reference pressure, which resulted in a minimum oil shrinkage
for the separator tests available. Thus, gas gravity must first be corrected to
the value that would result from separation at 100 psig:
y, = y, [l + 5.912 x 10-5(y,)(T)log(p/l14.7)] (5-29)
where y, = gas gravity (air = 1) that would result from separator conditions of
100 psig
y, = gas gravity obtained at separator conditions of p and T
p = actual separator pressure, psia
T = actual separator temperature, OF
yo = oil gravity, OAPI
For both dissolved gas and oil formation volume factor, improved correlations
were obtained when the measured data were divided into two groups, with the
division made at an oil gravity of SOOAPI. The expression for dissolved gas
was presented:

R, = C,~~,P~=P{C,[~,/(T 460)11 (5-30)
+
Values for the coefficients are as follows.

Coefficient yo I 30 Yo > 30

Cl 0.0362 0.0178
c2 1.0937 1.1870
c3 25.7240 23.9310

For saturated oils (reservoir pressure less than bubblepoint), oil formation
volume factor was expressed as:

The values for the coefficients depend on oil gravity and are given by the
following:

Coefficient yo 5 30 Yo > 30

Cl 4.677 x 4.670 x
c, 1.751 x 1.100 x 10-5
c, - 1.811 x lo-* 1.337 x
Since the oil formation volume of an undersaturated crude depends on the
isothermal compressibility of the liquid, the oil formation volume as pressure
is increased above bubble-point pressure was calculated from: