PETRONIUS, GULF
OF MEXICO, USA
The Petronius
field is located in Viosca Knoll, block 786, approximately 130
miles (208km) south-east of New Orleans. It lies in water depths
of 1754ft (535m). The field was discovered in 1995 and contains
estimated recoverable reserves of 80-100 million barrels of oil
equivalent. Petronius has been developed by a compliant tower
- the largest free-standing structure in the world. The cost of
the project has been put at $500 million. Texaco (the operator)
owns 50% of the field and the remaining 50% is owned by Marathon.
DEVELOPMENT
The field
is being depleted by 17 wells including ten producing wells and
seven water-injection wells. The estimated peak injection is 72,000
barrels of water per day.
DESIGN
Unlike conventional
platforms that are designed to resist forces, the compliant tower
is designed to flex with the forces of waves, wind and current.
The design specified a height of 1,870ft and a weight (including
two tower sections, a foundation template, piles and conductors)
of 43,000t. The tower accommodates 21 well slots.
The jacket
supports topsides of 7,500t. This houses the necessary process
equipment for a production capacity of 60,000 barrels of oil per
day and 100 million ft³ of gas per day.
CONTRACTS
The $140 million
contract for construction of the compliant tower was awarded to
J Ray McDermott. McDermott also handled the installation of the
entire structure, while the Houston-based McDermott Engineering
performed engineering design work. Gulf Island Fabrication, based
in Houma, won a $50 million deck fabrication and integration contract,
while WH Linder & Associates won the $10 million contract
for engineering design work of the topsides and the procurement
support.
The topsides
are 210ftx140ftx60ft-tall and contain all processing equipment,
water-injection facilities, export pipeline pumps and miscellaneous
utilities for the platform operation. The topsides also support
a full drilling-rig spread.
INSTALLATION
In 1997, the
subsea templates were put into place and the mooring foundation
piles were driven into the seabed. The mooring system is based
on 12 piles, three located at each corner leg, which extend from
the tower legs through the mudline, 450ft into the seabed. These
piles provide the foundation capacity and they were designed to
allow the tower to stay within an envelope of a 25ft sway (7.6m),
with a 10ft (3m) rotation sway at the surface.
The 4000t
North Module was installed at the end of November 1998. However,
during the subsequent offshore lift to install the 3600t south
module on 3 December 1998, one of the two 18,000ft, 2.25in working
lift cables broke and unsheathed on the DB50. This resulted in
the $70 million module falling to the seabed and damaging the
installation barge itself. But as the lift happened 1400ft away
from the tower itself, the accident did not affect the integrity
of the jacket.
After the
incident, Texaco assembled a project team tasked with reducing
the construction time from the original 27-month period. The replacement
module containing production equipment, waterflood equipment and
crew quarters, was built in 12 months at Gulf Island Fabrication
in Houma.
In May 2000,
Texaco installed the second deck module. The installation contractor
Saipem lifted the 3,850t deck module and set it on the existing
tower. Saipem's S7000 derrick barge used one of its two 7,700t-capacity
cranes to perform the lift.
EXPORT
Oil will be
exported via a 14in, 20-mile pipeline. Gas will be exported through
a 12in, 12-mile gas pipeline.
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Building of the Petronius module, at Houma. |
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