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Frontiers April 2005
17
nly when you stand alongside the
Thunder Horse production-drilling-
quarters (PDQ) platform can you
really appreciate the sheer scale and
complexity of this mighty floating structure.
Look up from the quayside and the PDQs
twin state-of-the-art drilling derricks tower
130m above you. Take a 60-second elevator
ride up to the PDQs deck and be greeted by
a topsides area the size of three football
fields, packed with equipment and systems
capable of treating and exporting a quarter of
a million barrels of oil per day. Then descend
through one of the 23m-wide columns to
below the water line and make a circuit
inside the rectangular pontoon of the hull
which forms the unseen base of this giant
semisubmersible youll cover more than
400m on a wide walkway surrounded by over
150 watertight ballast compartments.
one
As Frontiers went to press,
the production platform for
BPs Thunder Horse oil and
gas field the largest offshore
installation of its kind in the
world was in final preparation
for being installed in the deep
waters of the Gulf of Mexico.
Terry Knott talked with the
Thunder Horse project team
prior to sailaway to learn how
they met the challenge of
delivering this remarkable
engineering achievement
O
>>
PHOTO
AND
FRONT
COVER
BY
MARC
MORRISON 18
Frontiers April 2005
Impressive statistics abound for the
Thunder Horse PDQ, the largest production
semisubmersible ever built, which in
operation will have a displacement of
130,000 tonnes a significant step beyond
the previous largest production semi with
displacement of 85,000 tonnes in the Åsgard
field offshore Norway. But perhaps all things
on a grand scale are no less than should be
expected for a platform that for the next
25 years or more will
be the oil and gas
production hub for
the largest
hydrocarbon
discovery to date in
the Gulf of Mexico,
tapping into a
reservoir lying some
6000m beneath mud,
rock and salt, topped
by 1900m of ocean, which yields its
hydrocarbons at pressures over 1200 bar and
temperatures of 135C, conditions rarely
encountered anywhere in the offshore world.
Delivering offshore facilities on this scale
has been one of the greatest challenges on
the project, explains BPs Mike Janssen,
project general manager of the Thunder
Horse development, in which BP holds a
75% stake as field operator alongside partner
ExxonMobil. But the challenges of Thunder
Horse have not only been posed by scale.
In parallel with executing one of the largest
offshore projects yet undertaken, the project
team, supported by BPs technology experts
around the globe, have also successfully
managed a major technology innovation and
development programme to
enable us to handle the
combination of high
pressure, high temperature
(HP/HT) reservoir
conditions, very deep water
location, and the large
hydrocarbon volumes.
There were many
technology gaps to fill when
we started out, and weve
pushed beyond existing limits on many
fronts. The result is a world class engineering
achievement, a pioneering step akin to those
needed in the past to open up the North Sea
or the north slope of Alaska, which will be of
benefit to BPs future deepwater projects
and to the wider industry.
One example of the many fronts
Janssen refers to is the drilling and
completion of some of the industrys longest
deviated wells from the fields four drilling
centres the PDQ will be located over one
of the centres allowing wells to be drilled
from the platform, with subsea wells
grouped in three other centres up to 6.8km
distant, tied back to the PDQ by seabed
flowlines. Handling the HP/HT conditions
plus high flowrates of up to 50,000 barrels
per day (bpd) through individual wells has
demanded the development of over 100 new
components for completing and operating
the wells (Frontiers, August 2004). And from
the wells, hydrocarbons will rise up to the
PDQ at the surface almost two kilometres
above through steel catenary risers. The
risers are longer and stronger than any
before, up to 600mm in diameter, with walls
thick enough to resist both high internal and
external pressures another example of
technology development by the project.
Large and stable
But it is the PDQ, to be stationed in the field
some 240km southeast of New Orleans, that
is the visible heart of the Thunder Horse
Weve pushed
beyond existing
technology limits
on many fronts
Main components of the
Thunder Horse PDQs
hull and topsides
Flare boom
Topsides modules
(power generation,
production, gas
compression)
Twin drilling derrick
(top is 130m above
base of hull pontoon)
Living quarters
Helideck
Hull columns
Hull pontoon
(below water)
>> Frontiers April 2005
19
project, says Mike Baur, responsible as
facilities manager for the delivery of the
semisubmersible platform, valued in excess
of $1 billion.
The unique conditions of Thunder Horse
have combined to give the PDQ its shape
and scale, notes Baur. A semisubmersible
provides us with a large and stable installation
which can carry the high operating loads
imposed by the processing and drilling
requirements, while at the same time
supporting the additional loads of the dozen
or so massive risers weighing around
400 tonnes each that will hang off the hull,
and the 16 deepwater chain and wire mooring
lines that anchor the semi in 1844m of water.
The PDQ is also designed to survive a once-
in-a-hundred-years storm, and withstand the
hurricanes and high seasonal ocean currents
which occur in the Gulf of Mexico.
Take all these factors together, and the
result is this very large, robust platform, with
accommodation for 229 persons, unique in
both its size and the duties it will perform.
The PDQ processing facilities are
designed to handle incoming HP/HT
wellfluids and export 250,000bpd of oil,
5.6 million m
3
per day of natural gas, treat
140,000 bpd of produced water and inject up
to 300,000bpd of mixed produced water and
seawater into the reservoir for pressure
maintenance. This capability is provided by
three large topsides
modules
production,
compression and
power generation
which together weigh
around 18,000
tonnes, creating by
far the largest
topsides in the Gulf
of Mexico. The
installed power
generation capacity totals 100 megawatts
(MW) enough to supply a town of around
80,000 homes, and the biggest offshore
power generation plant in the world.
Oil and gas from the field, expected by
the end of this year, will be exported from
the PDQ in separate pipelines connecting
into the main Mardi Gras transmission
system, operated by BP, and thence to shore.
Global operation
The Thunder Horse field was discovered in
1999, with the basic execution plan for the
project and concept for the PDQ decided by
early 2001 (Frontiers, September 2001).
Detailed design of the PDQ began later that
year, the hull being designed by GVA of
Sweden, an established leader in
semisubmersible vessel design, while the
topsides modules were designed by
Mustang Engineering in Houston.
Construction of the topsides modules,
beginning early in 2002, was carried out by
J Ray McDermott in Morgan City, Louisiana
the fabrication yard was dedicated to
Thunder Horse and BPs other Gulf of
Mexico deepwater
projects, Holstein, Mad
Dog and Atlantis, which
were being progressed
simultaneously.
Construction of the
semisubmersible hull
began later in 2002 at the
Okpo fabrication yard of
Daewoo Shipbuilding and
Marine Engineering
(DSME) in South Korea.
Integration of hull and topsides the
completion of the PDQ was conducted at
Kiewit Offshore Services in Ingleside, Texas,
prior to the PDQ being towed to the field.
The diversity of contractors spread
around the globe presented its own set of
interface management and logistics
challenges, adds Baur. The scale of the job
meant we needed nine delivery teams,
working in different cultures, which created
many engineering interfaces far more than
usual for which we had to ensure that
technical specifications, dimensions and
weight, and delivery schedule were all tightly
controlled. Careful co-ordination between
teams resulted in no significant mismatches
the modules were installed on the 15,000m
2
deck at Ingleside to within an accuracy of
20mm, and the topsides weight came in a
few per cent below contingency budget.
Outstanding performance.
Though only one part of the overall
Thunder Horse development, the PDQ
ranks as a major project in its own right,
as exemplified by the manhours required
to deliver it, adds Kevin Devers, manager
of project engineering.
Design and fabrication effort for the PDQ
will amount to around 15 million manhours
by the time it sails from Texas, says Devers.
At peak, we had teams of 2700 people
working on hull fabrication and 1200 on the
topsides modules. As on all BP projects,
safety has been of prime importance, and at
the outset we initiated a safety awareness
and training programme across the
contractors and vendors involved, with the
result that in all these hours worked we have
achieved an excellent safety record.
Measured by the industry standard of
number of incidents per 200,000 manhours
worked, the PDQ has achieved a total
recordables incident rate of 0.43, and a
days away from work rate of 0.04, ranking
the project in the top industry quartile for
safety performance.
Building blocks
Baur and Devers attribute much of the
success in delivering the PDQ to the team of
seasoned veterans working on the project,
and the continuity achieved as they moved
through the design, construction and
integration stages of Thunder Horse.
One of those veterans is Steve Byatt,
a founder member of the Thunder Horse
team working on the design of the hull,
Construction of
the PDQ ranks in
the top industry
quartile for safety
performance
Construction of the PDQ hull took place in a vast dry dock at Okpo in South Korea. Contractor DSME
fabricated 330 separate structu