Page 85 - Handbook Of Multiphase Flow Assurance

80 4. Hydraulic and thermal analysis

40
V SL =0.9 m/s, V SG =0.2 m/s
35

30
Pressure, [psia] 25
20

15
No Modification
10 Modification One
Modification Two
5
Modification 3
0
0 50 100 150 200 250 300 350
Time, [s]
FIG. 4.6 Effect of flowline arrangement on backpressure fluctuations.

Besides severe slugging or liquid loading control, the method may be extended to optimize
gas lift effectiveness as in riser-based gas lift systems. Method may help extend production of
tiebacks with terrain slugs or declining and water-producing fields by recovering loaded up
production stopped by severe slugging. Method may help reduce slug vibration by breaking
large slugs into smaller ones, or to homogenize multiphase flow at subsea boosting pump
intake. With no moving parts or electronics, the method is expected to have higher reliability.

Multiphase flow liquid holdup—Vertical vs horizontal
In steady state operation the holdup averaged over large length does not change in ver-
tical or horizontal flow, however local holdup can change in slug or churn flow. Multiple
correlations have been developed to calculate the liquid holdup value in either vertical or
horizontal configuration. Liquid holdup and entrainment in vertical flow are related to the
liquid loading of wells.
A correlation developed by Turner et al. (1969) based on Hinze (1955) flow equations by
balancing gravity and drag forces acting on a droplet and updated by Coleman et al. (1991)
allows one to estimate the minimum gas velocity in a well at which liquid entrainment will
be sufficient to lift the liquids to surface. The Turner correlation was found to have a closer
match to field data in Marcellus shale (Child and Brauer, 2017). It may be used with well-
head pressures over 1000 psi or 70 bar to find the minimum gas velocity u in feet per second
to lift water or oil.

1 1
σ 4 (ρ − ρ G ) 4
u = 1 912 L
.
1
ρ G 2
The density of gas is proportional to pressure, and densities of liquid may be assumed
3
3
as 45 lb m /ft for oil and 67 lb m /ft for salt water. As the typical surface tension for gas-oil is