TOP 5 PROJECTS
Total adopts all-electric, subsea multi-phase
approach for mixed-crude CLOV development
In June, Total lifted frst oil from CLOV, its fourth deepwater development “pole” in block 17 offshore Angola. Like its pre- decessors Girassol, Dalia and Pazfor, CLOV routes production through a network of subsea fowlines to a spread-moored
FPSO. Total took onboard experiences from
these earlier projects to address certain issues, notably the treatment of two different
types of crude. But CLOV also features innovations designed to improve recovery and
operational effciency, as well as raising the
bar in terms of local construction content.
The development takes in the Cravo,
Lirio, Orquidea, and Violeta felds, with
proven and probable oil reserves of 505
MMbbl. The felds cover 381 sq km (147 sq
mi) in water depths of 1,100-1,400 m ( 3,609-
4,593 ft), 140 km ( 87 mi) from Luanda, and
40 km ( 25 mi) northwest of the Dalia hub.
Reservoir conditions vary, with different
temperatures, pressures, and oil qualities.
The Oligocene Cravo and Lirio reservoirs
produce 32-35°API crude which quality-wise
is one of the best in block 17. Orquidea and
Violeta’s Miocene produces 20-30° API oil,
which is more permeable and viscous.
Development drilling started in 2012. Total
and its partners Statoil, ExxonMobil, and BP
plan to tie a total of 34 wells back to the FPSO,
which has oil processing capacity of 160,000
b/d, storage for up to 1. 8 MMbbl, and gas handling capacity of 230 MMcf/d ( 6. 5 MMcm/d).
Engineering, procurement, and construction
contractor Daewoo Shipbuilding & Marine
Engineering (DSME) cut frst steel in July
2011 and completed the vessel two years later.
Construction required supply of about 88,000
steel plates, supplied by POSCO.
KBR performed detailed engineering and
design of the topsides in collaboration with
DSME.
The vessel is designed to process and
store the different types of crude simulta-
neously, while its hull incorporates tanks to
separate the produced oil from water. DSME
contracted VWS Westgarth to design and
supply ultra-fltration equipment with a ca-
pacity of 66,208 cu m/d ( 2. 34 MMcf/d), and
a sulfate removal package with treatment
capacity of 59,496 cu m/d ( 2. 1 MMcf/d).
Grenland Group provided the vessel’s Mi-nox deoxygenating system which can treat
up to 280,000 b/d of water used for injection,
while Sulzer engineered the electric motors
for the water injection pumps.
This is Total’s second all-electric FPSO and
its frst to be equipped with variable-speed
drive (VSD) systems to help control energy
consumption. The confguration is designed
to maximize energy effciency by generating only the quantity of electricity needed to
operate the facilities. Under a $113-million
contract, GE supplied four LM2500+ G4 SAC
aero-derivative gas turbines for power generation and fve gas compressors, while GE
subsidiary Converteam manufactured fve
VSD systems, including induction motors, for
the compressors. During normal operations
there is no faring, with recovery of heat from
the turbine exhausts and of vent gases.
CLOV’s processed crude is transferred
regularly to tankers via two 2-km ( 1.2-mi) long
reinforced rubber oil offoading lines (OOLs)
connected to an offshore loading buoy. Total
claims that the wider than normal diameter of
the OOLs (24-in.) allows the crude to be transferred directly in the allotted transfer time,
dispensing with the normal booster pumps.
According to Cyril de Coatpont, in charge of
CLOV’s subsea pipeline/oil offoading systems,
the pipes, which are designed for a service life
of up to 20 years, can cope with pressures up to
30 bar (435 psi). “They have to be reinforced to
be able to withstand the water ‘hammers’ that
can accidentally occur during offoading opera-
tions.” To meet these specifcations, OOL de-
signer and manufacturer Trelleborg in France
tightened the manufacturing procedures, in-
creasing the number of crossed metal frames
between the various layers of rubber that make
up the pipes.
CLOV’s produced gas is exported via a
subsea pipeline to the onshore Angola LNG
plant.
Countering pressure drop
FMC Technologies manufactured the sub-
sea production equipment under a $520-mil-
lion contract. This comprises 36 EVXT 10,000-
psi (689-bar) subsea tree/wellhead systems
with a tree bore size of 51⁄8-in. x 21⁄16-in., and sev-
en manifold systems. Aker Solutions, in col-
laboration with Framo Engineering, supplied
a 10.6-km ( 6.5-mi) multi-phase power and con-
trol umbilical that provides system functions
for the two Framo-engineered multi-phase
pump station (comprising two pumps, one for
standby duty only), installed on the seafoor in
a water depth of 1,170 m ( 3,838 ft). The pump-
ing system will be used to increase pressure in
wells extracting the more viscous oil from the
Orquidea and Violeta felds, allowing produc-
tion levels to be maintained after three years
of operations as reservoir pressure declines.
The multi-phase, helico-axial system ac-
commodates a mixture of oil, gas, and water
at high speeds. According to CLOV’s deputy
director Francois Bichon, this is the frst time
Total has adopted such a solution, and the
company plans to add two four-pump mod-
ules for its GiRI (Girassol expansion) project.
Jeremy Beckman
Editor, Europe CLOV is Total’s first FPSO with
variable-speed drive systems.
(Photo courtesy Bureau Veritas
and Total)
