Page 84 - Handbook Of Multiphase Flow Assurance

Hydrodynamics of multiphase flow 79

Comparisons of multiphase flow correlations and related experimental work is provided
by Shea et al. (1997), and Carrascal (1996).
Slugging in itself is detrimental as it can reduce the production rate. Slugging also re-
duces production by increasing backpressure on the well. One reference to an example of
a severe slugging flow reducing production by 20% was shown in Montgomery (2002).
Slugging also causes periodic impacts at elbows which may affect mechanical integrity
(Hill and Wood, 1994).
Extremely long liquid slugs can be created when downward sloping pipelines lead to riser
pipes in deepwater operations. These “severe slugs” can cause serious upsets in separation
processes, high pipe vibration and stresses during the arrival stage, and paraffin deposition
problems near the riser base.

Designing out severe slugging

Production system may be designed to minimize severe slugging by routing the flow
predominantly uphill. This is the common design technique used by offshore operators.
However, in onshore production in shale wells it may be more beneficial to route the flowing
the lateral portion of the well downhill, in a so-called toe-up configuration. Although this
approach in shale causes more flow instability, it allows liquids to accumulate at the well heel
location which then may be lifted to surface using artificial lift methods.
A novel method to control slugging was recently proposed (Makogon et al., 2011,
US8393398). The system has no automation or moving parts and was shown in pilot-scale
tests to help reduce slugging. It may be installed during initial construction or retrofitted to
an existing system. After the concept model of severe slugging control method showed that
slugging was eliminated in a multiphase flow simulator, the pilot tests quantified the range
of the method performance in a 3-in. diameter 20 m pipeline—14 m riser or lateral-vertical
flow geometry.
The effect is shown in the charts below in Fig. 4.5 indicating flow regime maps without and
with the method installed.
Not all combinations of gas and liquid velocities were affected equally, but in multiple
cases the method was effective.
Flow stability was achieved at lower superficial gas velocities. Backpressure fluctuations
were reduced or eliminated as data in Fig. 4.6 shows. An example of complete elimination
shows backpressure fluctuation without and with the method implemented.

10 10
Severe
Slugging Severe
Transition Slugging
Transition
Stable Stable
V SL [m/s] 1 V SL [m/s] 1

0.1 0.1
0.1 1 10 0.1 1 10
V SG, 0 [m/s] V SG, 0 [m/s]
FIG. 4.5 Effect of flowline geometry on severe slug suppression.