Abstract:
Slugging involves pressure and flowrate fluctuations and poses a major threat to
optimising oil production from deepwater reserves. Typical production loss could be as
high as 50%, affecting the ability to meet growing energy demand.
This work is based on numerical simulation using OLGA (OiL and GAs) a one-
dimensional and two-fluid equations based commercial tool for the simulation and
analysis of a typical field case study in West Africa. Numerical model was adopted for
the field case. Based on the field report, Flow Loop X1 consisted of well X1 and well X2,
(where X1 is the well at the inlet and X2 is the well connected from the manifold (MF)).
Slugging was experienced at Flow Loop X1 at 3000 BoPD; 4MMScf/D and 3%W/C. This
study investigated the conditions causing the slugging and the liquid and gas phase
behaviour at the period slugging occurred.
The simulation work involved modelling the boundary conditions (heat transfer, ambient
temperature, mass flowrate e.t.c). Also critical was the modelling of the piping diameter,
pipe length, wall thickness and wall type material to reflect the field geometry.
Work on flow regime transition chart showed that slugging became more significant from
30% water-cut, especially at the riser base for a downward inclined flow on the pipeline-
riser system.
Studies on diameter effect showed that increasing diameter from 8” – 32” gave rise to a
drop in Usg (superficial velocity gas) and possible accumulation of liquids on the riser-
base position and hence a tendency for slugging formation. Depth effect study showed
that increasing depth gave rise to increasing pressure fluctuation, especially at the riser-
base.
Studies on the Self-Lift slug mitigation approach showed that reducing the internal
diameter of the Self-lift by-pass pipe was effective in mitigating slug flow.
S3 (Slug suppression system) was also investigated for deepwater scenario, with the
results indicating a production benefit of 12.5%.
In summary, the work done identified water-cut region where pipeline-riser systems
become more susceptible to slugging. Also, two key up-coming slug mitigation strategies
were studied and their performance evaluated in-view of production enhancement.
