HIBERNIA, JEANNE
D'ARC BASIN, CANADA
Hibernia is
located in the Jeanne d'Arc Basin, 315km east of St John's, Newfoundland,
in water 80m deep. The field consists principally of two early
Cretaceous reservoirs - Hibernia and Avalon - located at average
depths of 3700m and 2400m, respectively. Hibernia oil is a light
sweet crude, with a density of about 32° to 34° API and a sulphur
content, by weight, of 0.4-0.6%. The field contains approximately
three billion barrels of oil in-place, and recoverable reserves
are estimated to be at around 615 million bbl.
DEVELOPMENT
OF HIBERNIA
It was decided
that the Hibernia field would be developed using a special gravity-base
structure, strong enough to withstand a collision with a one-million-tonne
iceberg (expected to occur once every 500 years) and a direct
hit from a six-million-tonne iceberg (expected just once every
10,000 years).
GRAVITY BASE
STRUCTURE
In September
1990, HMDC awarded the gravity base structure (GBS) contract design
to Newfoundland Offshore Development Constructors (NODECO). The
detailed design was subcontracted to Doris Development Canada
(DDC).
The Hibernia's
novel 450,000t gravity base structure design consists of a 105.5m
concrete caisson, constructed using high-strength concrete reinforced
with steel rods and pre-stressed tendons. The caisson is surrounded
by an icewall, which consists of 16 concrete teeth. Structurally,
the 1.4m-thick icewall is supported by a system of X and V walls,
which transmit the loads to the interior tiewall. The X and V
walls have a thickness varying from 0.7m to 0.9m and the tiewall
has a thickness of 0.9m. Put together, these walls form the icebelt.
The caisson is closed at the bottom and top by horizontal slabs
and the base slab has a diameter of 108m. The upper top-surface
slab is about 5m above sea level.
Inside the
gravity structure are storage tanks for 1.3 million bbl of crude
oil.
Four shafts
run through the GBS from the base slab to support the topsides
facilities: namely the utility shaft, the riser shaft and two
drill shafts. Each of the shafts are 17m in diameter and extend
to a total height of 111m.
The utility
shaft houses the mechanical outfitting required to operate the
GBS system. It includes pipework, heating and air-conditioning,
and electrical controls. The two drill shafts each house 32 drill
slots to accommodate the wells, which will reach depths of more
than 3700m below sea level, down into the oil reservoirs.
TOPSIDES
The topsides
have a design capacity of 23,900m³/d (150,000 b/d), based
on the 98 million m³ (615 million barrel) estimate. The topside
facilities consist of five super-modules (processing, wellhead,
mud, utilities, and accommodation for 185 people) as well as seven
topside mounted structures (helideck, flareboom, piperack, main
and auxiliary lifeboat stations, and two drilling modules).
The wellhead
module for Hibernia was fabricated at Bull Arm, while the remaining
components were made in construction sites located around the
world - two in Italy and the remaining two in South Korea. Four
of the topside mounted structures (flareboom, helideck, main and
auxiliary lifeboat stations) were also fabricated at Bull Arm.
The other three topside mounted structures (components of the
two drilling rigs and the piperack) were fabricated in Newfoundland
and New Brunswick, with some of the components being built in
Alberta.
MATING
The 37,000t
integrated topsides facility was transported by barges to the
Hibernia deepwater site and positioned above the partially submerged
GBS shafts to form the completed 600,000t production platform.
This was then towed to its final site and 450,000t of solid ballast
was added to secure it in place.
OFFSHORE
LOADING SYSTEM
Oil stored
in the GBS will be exported by means of an offshore loading system
(OLS) consisting of subsea pipelines, a subsurface buoy and flexible
loading hoses, feeding a purpose-built shuttle tanker.
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A topside drilling cabin. |
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