Combined efforts on
TOTAL’s CLOV FPSO
MARIN carried out model tests, real-time simulations and a­
full-scale monitoring campaign considering different operational
and design aspects of the CLOV FPSO, installed off Angola.
Dimitri van Heel, Janou Hennig & Pieter Aalberts, d.v.heel@marin.nl
Photograph: Igor Sachs - TOTAL E&P Angola
T
OTAL operates the Block 17 oil
field, which is located approxi­
mately 80 miles off the coast of
Angola. CLOV is the fourth FPSO installed
in this area and like the other FPSOs, it is
spread moored to the seabed. An offshore
offloading buoy (SPM) is installed in the
same field.
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report
Tug optimisation study During the
start-up period drill ships may be operating
in the vicinity of the FPSO and their pres­
ence constitutes a possible risk to offloading
operations at the FPSO or SPM. In a study
executed by MSCN, simulator runs were
conducted to determine the number of tugs
needed for operations at CLOV. The simula­
tions focused on emergency situations in
adverse weather conditions (strong currents,
squalls) and looked at the tug assistance
­required to resolve the situations and keep
the export tanker clear from any objects in
the area.
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Model tests Seakeeping, towing stability
and mooring tests, tug optimisation and
hull integrity have all been examined
over the last three years. In 2011, MARIN
carried out model tests on the CLOV FPSO
on behalf of DSME, examining seakeeping,
towing stability and mooring. Apart from
the wide range of model tests and para­
meter variations, some challenges were
­encountered in realising asymmetrical
weight distributions at relatively low pitchroll coupled moments of inertia. While
the model dimensions and scale could be
called standard, a slight change in the
weight distribution could lead to a signifi­
cant change in the FPSO model’s motion
behaviour; this order of magnitude corre­
sponds to the shift of a small ballasting
weight by a centimetre. DSME and MARIN
were able to quantify the effect on motion
RAOs and the MARIN project team made
sure that the weight calibration was to the
point by using very accurate measurement
and calibration methods.
Real-time simulations are the best way
to guarantee that emergency actions are
carried out in a realistic manner. The deci­
sion-making process and limitations caused
by ship specific characteristics and the
­environment are all taken into account. The
outcome of the simulations was combined
with results from earlier studies. By combin­
ing these results with the normal operation
schedule, a picture was compiled of the
­optimum tug fleet needed to guarantee safe
and efficient operations at the offloading
terminals. The lessons from this study were
carried forward to the simulator training
sessions that are still regularly performed
for mooring masters and tug captains.
in an easily understandable format.
After successful implementation of this
­system on the USAN FPSO in 2009, TOTAL
also decided to implement the system on
the CLOV FPSO. The hull monitoring system
- comprising a number of strain type sensors,
Exe certified junction boxes and main
­cabinet - was installed on board during the
construction of the FPSO by DSME in Korea.
Since the departure of the FPSO in October
2013, the system has been continuously
monitoring the fatigue loads. Currently, the
hull monitoring system software is being
configured at MARIN and will be installed
mid-2014 during the final commissioning of
the FPSO offshore Angola, which enables
the operator to keep a continuous eye on
the lifetime consumption of the FPSO.
Improving hull integrity by monitoring The fatigue assessment of an FPSO hull
CLOV FPSO model tests
is a difficult but important design aspect of
the permanently moored offshore structure
(see separate article). The Advisory Hull
Monitoring System (AHMS) developed within
the Monitas JIP is an advanced hull monitor­
ing system, which includes automatic and
extensive analyses of the monitoring data. It
explains reasons for potential deviation of
the actual lifetime consumption from design
predictions and translates the monitoring
data into operational guidance and advice
Real-time simulations
report
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