World-class welding technologies - Subsea 7

Planning and precision
combine on Pazflor
The successful installation by
Subsea 7 of three subsea separation
units (SSUs), operated by Total E&P
Angola, proved critical to the early
completion of the landmark Pazflor
project on Block 17, offshore Angola.
The challenging project involved the
world’s first deployment of vertical
SSUs to separate the oil, gas and
water produced from Pazflor’s
Miocene reservoirs.
Installing each SSU (weighing in excess
of 1,000t, including suction anchors)
required an unprecedented level of
precision in water depths around 800m
and a close working relationship with
Total and the SSU manufacturer, FMC,
to ensure the final design included
offshore installation requirements.
Operational requirements necessitated
exceptionally tight installation
tolerances of +/- 0.5° from horizontal
when installing the cluster of four
suction anchor foundations. To achieve
this target, Subsea 7 developed the
lifting arrangement, and interfaced with
FMC to accurately operate the levelling
system based on differential suction.
Early analyses showed a risk of
resonance of the subsea hardware
during lowering, potentially leading
to significant weather sensitivity. To
mitigate this issue, Subsea 7 developed
a real-time monitoring system receiving
acceleration data from sensors located
on the crane tip and on top of the
hardware as they were lowered.
Extensive dry and shallow water testing
in Norway allowed the team to test
the SSU installation before the units
were finally transported to Angola.
Working in close liaison with FMC,
Subsea 7 coordinated transportation
and designed a specific sea fastening
to minimise fatigue of the SSUs. Prior
to deployment on site by Subsea 7’s
installation vessel the Acergy Polaris,
the structure’s integrity was re-tested in
Luanda bay.
Connecting each SSU to the subsea
manifold was a complex and delicate
operation in which the ROV operators
had to first remove caps from the
SSU shallow water tests in Norway
manifold followed by the operation of
a jacking system to slide the 400t, sixstorey
high SSU towards the manifold to
mate three connections simultaneously.
The Seven Eagle performed the SSU
umbilical installation and the tie-in of the
first pair of four multi-phase pumps.
The landmark project, in which first
oil was achieved ahead of schedule
including the development and
installation of new technology,
underlines the importance of effective
interfaces between suppliers,
contractors and client.
Subsea 7 continues to develop new
deployment systems including fibrerope
and active-heave compensation
that are deemed essential in the
deployment and retrieval of sensitive
rotating machinery and processing
systems in ever-increasing water depths
of the future.
A Pazflor SSU being installed
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seabed-to-surface