time. The low-pressure filling pump was moved from the pumping
skid to the flooding skid to enable one skid to perform both functions. These changes were designed to reduce the number of deployments and improve diagnosis of any performance issues with
the unit or ROV, leading to a reduction in vessel time and lower overall costs to the client.
Hydro-testing and MEG spool leak testing for the gas export sys-
tem was conducted in four stages, as follows:
• Hydro-testing the single hybrid riser (SHR), including the flex-
ible jumper, from the flexible end, and installation of main line
spools and subsea isolation valve (SIV)
• Hydro-testing gas export flowline, SHR, and flexible jumper as
one complete system
• MEG leak test and nitrogen purge of the spool, followed by
installation of a check valve at a discharge point on the subsea
pipeline and manifold (PLEM) connecting the rigid pipeline
with the existing gas export system
• Flushing the permanent cap and FLET pipework up to the main
isolation valve and leak testing the cap, both with dyed MEG.
Barrier leak testing of the live PLEM was performed using MEG
to ensure the system was safe for the spool installation, in parallel with new procedures agreed to with the client. Adaption to the
changing schedule and methodology was important to efficiency improvements as the project progressed.
The project’s two production loops
and four water injection systems were
hydro-tested independently after all
main system components had been
mechanically completed. The produc-
tion loops and water injection systems
were subjected to a 24-hour hydro-test
with a test medium of filtered, treated,
and dyed seawater. After the hydro-
test was accepted, the pressure in the
system was reduced to atmospheric pressure in a controlled man-
Custom manifolds allowed the vessel to perform leak tests with
the assistance of a remote logger and ROV. The manifolds allowed
three systems to be hydro-tested simultaneously and monitored independently. The approach reduced the number of deployments and
freed the vessel from a 24-hour monitoring period, allowing it to be
used for other filler works, which optimized total cost. The extended
testing period provided more test parameter information, which provided the basis for a faster decision on test results. Detaching the
vessel from the testing system enhanced safety.
Gas export dewatering
Gas export dewatering was carried out from the flexible jumper
FPSO end toward the gas export FLET. The flexible jumper end was
recovered onboard the main installation vessel (MIV). The dewatering pig launcher was preloaded with six dewatering pigs that were
propelled with compressed nitrogen from the FPSO flexible end to
the gas export FLET temporary pig receiver located subsea.
The dewatering nitrogen spread was located on the dewatering
vessel and connected to the MIV via a 2-in. hose, while the support
vessel assisted in operations at the receiving end.
Dewatering was accepted with all pigs in the receiver and a MEG
concentration above 95%, according to support vessel sampling.
When the 12-in. (273-mm) x 13.8-mi (22-km) pipeline was dewatered, it was packed with nitrogen at 13 barg above static head pressure at the receiving end (130 barg).
Key aspects of the dewatering operation (which consisted of
MEG swabbing, dewatering, drying, and packing) included producing nitrogen at a purity of 95% or greater and a dew point of - 40°C or
better at atmospheric pressure.
Equipment used for the dewatering operations was sized to maintain a minimum pig speed of 0.15 m/s at 135 barg. The pigs were
steel-bodied and capable of negotiating 5D bends in the pipeline.
Three were equipped with electromagnetic transmitters with a battery life of two months. All six were equipped with magnets to confirm passage.
Subsea MEG sampling
Prior to dewatering operations from the main installation vessel,
a pig receiver was installed, and FLET valve positions were aligned.
Pig signaling devices were installed at the upstream pig launcher
and the MEG sampling tool at the pig launcher 2-in. stab receptacle.
After launching the dewatering pigs, an ROV was deployed from
the support vessel at the receiving FLET to confirm receipt of the
pigs and to operate the MEG sampling tool. MEG samples were taken from four slugs, with special attention given to the last slug between pigs
five and six. The tool was then recovered by the support vessel, and MEG
was tested for changes in density. Additional MEG samples were stored in
sealed bottles for further analysis by
the client. This subsea sampling was
able to confirm MEG quality in the
field, giving the client assurance of a
Umbilical services included pre/
post load-out testing before or after
transfer to the installation vessel;
transpooling monitoring and lay moni-
The nitrogen dewatering spread is aboard the dewatering vessel,
ready for deployment.
The subsea MEG sampling skid
tested for changes in density.