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Instrumentation and Measurement 53

Void fraction Volume fraction

GVF 0.80
e = 0.50
g
e = 0.15 OVF 0.05
o
e = 0.35 WVF 0.15
w

Fig. 2.8 A cross-section of the pipe showing a stratified flow pattern with calculated gas,
oil, and water void fractions with the corresponding gas, oil, and water volume fractions.

and 0.7 is defined as multiphase flow (gas condensate, volatile oil,
water cut over 30%). Below 0.3 could be considered liquid single
phase (black oil with low gas/oil ratio (GOR), heavy oil, high water
cut >70%).
2 Another important factor is gas volume fraction (GVF vol ), which is
estimated as the ratio of the total gas flow to the total rates of water,
oil, and gas. The e g and GVF vol are unequal and different levels of
thresholds. When GVF vol is higher than 0.90, it is considered gas
single phase (dry gas or wet gas), between 0.5 and 0.89 is defined
as multiphase flow (gas condensate, volatile oil, water cut over
30%). Below 0.5 could be considered as liquid single phase;
however, GVF vol and GVF area are related through the following
expression 2.5:
If gas and liquid travel at different velocities:

Vr ¼ V g V l slip velocityð Þ (2.3)
So slip ratio can be calculated as:

(2.4)
k ¼ V g =V l
Assuming that the gas velocity is five times the liquid velocity, then k¼5.0
and the fraction of gas occupied in the pipe is e g ¼0.8.
The GVF vol is

e ∗ k
GVF vol ¼ (2.5)
1 e + e ∗k

GVF vol ¼95% and the fluid is gas single phase.