by many years, BP decided to substantially
update, replace, and increase the capacity of
the field’s already vast subsea infrastructure.
In full, Quad 204’s work scope included a large-
scale modernization and redevelopment of the
subsea infrastructure and a plan to drill up to 20
new wells. The new Glen Lyon FPSO would be
connected to a combination of legacy and new
subsea infrastructure to restart production.
In a statement, Group Chief Executive Bob
Dudley said that Quad 204 was “one of the
largest recent investments in the UK,” with
the company claiming to have delivered more
than £ 2 billion ($2.5 billion) of investment to
Production was stopped in the Schiehallion
Area in early 2013 to allow for work on the
Quad 204 project to begin. Many systems
needed to be removed or replaced to different
degrees, as well as expanded.
Train described the redevelopment’s subsea
system as “one of the largest, if not the largest
in the world.” The company worked with Wood
Group Kenny on the subsea design engineer-
ing, various legacy equipment suppliers and
Technip for installation and flexible pipe supply.
Schiehallion Area has five drill centers, Central,
West, North, North West, and then, separately,
Loyal’s drill center. It currently has 52 wells,
and another 20 new wells are envisaged as
part of the Quad 204 redevelopment, bringing the field’s potential total up to more than
70 subsea wells. Of the planned 20 new wells,
part of a £ 1.3-billion (more than $1.6-billion)
drilling campaign, Train said that eight have
been drilled at press time.
Quad 204’s subsea infrastructure comprises
of production, water and gas systems and an
integrated subsea control system. The produc-
tion system has virtually all been replaced
except for several existing manifolds, jumpers
and xmas trees on the existing wells. Produc-
tion capacity has been expanded by 50% with
15 new production flowlines replacing the
original 10. The water injection system mainly
comprises the existing equipment along with
some expansion; namely, two additional mani-
folds and various jumpers to allow the tie-in
of the planned new wells. The gas lift system
was primarily left intact and upgraded to run
at higher flow rates to serve the additional
wells while the control system was completely
replaced to improve reliability and provide
For the new, substantially larger FPSO to
connect to the subsea infrastructure, all the
gas, water, and production risers were replaced,
along with two dynamic umbilicals, and the
mooring system completely replaced. The com-
pany claims that the risers have the largest
bend stiffeners in the world designed to protect
the risers as they interface with the FPSO tur-
ret and accommodated vessel movement in the
harsh west of Shetland environment.
Glen Lyon FPSO
Constructed at the Hyundai Heavy Industries shipyard in Ulsan, South Korea, the Glen
Lyon FPSO took four years to build. Anchored
by a weathervaning turret mooring system
that features 20 mooring lines almost 1 mi ( 1. 5
km) in length, replacing the 14-line mooring
system of the previous asset.
The Schiehallion FPSO was 230 m (755 ft)
long and 38 m ( 15 ft) across the beam, while
the new Glen Lyon asset is longer and wider at
270 m (886 ft) and 52 m (170 ft) respectively.
The main reason behind the increased size
is to accommodate the topsides process and
utilities systems required to process much
larger volumes of fluids that will be received
on the new FPSO.
Train said that so-called dry oil, hydrocarbons without any associated water, had already
been extracted, so Quad 204 would be produc-
ing wet oil with around 50-60% water cut. That
water would then have to be separated from
the oil, so the production facility on Glen Lyon
is designed especially with this consideration.
The higher water cut called for larger and additional separators, as well as more power, which
all adds up to more space and a larger FPSO.
Train said that a unique feature of Quad 204,
as a brownfield development, is that production, water injection and gas systems need to
be brought online simultaneously or within
a short period of start-up. The reservoir is
relatively low pressure and the high water cut
requires most wells to be gas lifted to produce.
A greenfield development is likely to produce
for a significant period before water and gas
systems are necessar y. This factor alone had a
major bearing on sequencing and integration
of design, equipment manufacture, installation
and the start-up sequence.
In replacing the Schiehallion FPSO, Train
said that the largest challenge presented was
the necessity to complete “a lot of destruct
before we could do any construct.”
The existing 18 risers were disconnected and
laid back on themselves before the 14 moorings
were disconnected and the FPSO removed
from the field. Once the FPSO was off station
the risers and equipment that remained had
to be recovered and returned onshore with
over 95% of materials recycled in an environ-
mentally sensitive manner. At the drill centers,
obsolete flowline jumpers and control leads
were removed to facilitate reconfigurations
and expansion of the infrastructure through
addition of manifolds for new well slots.
BP project managed the topsides hook-up
of the FPSO with Amec-Foster Wheeler as
the main construction contractor and the BP
Quad 204 by the numbers
• Location: 175 km west of Shetland in about 1,300 ft of water
• First oil: Schiehallion/ Loyal in 1998; Quad 204 in May 2017
• Life-of-field: 2035 and beyond
• Estimated resources: 450 MMboe
• Subsea: Seven new manifolds, the capacity has extended to beyond 75 wells. Of
the 21 risers, 15 are for producers, three are for gas risers, and three are for water
• Production: Claimed to be the world’s largest harsh environment FPSO, Glen
Lyon measures 270 m long by 52 m wide and weighs around 100,000 metric tons.
Deepsea Aberdeen will be used to drill the planned additional 20 wells in addition to
the original 29 wells. Glen Lyon can process and export up to 130,000 b/d and store
up to 800,000 bbl of oil. It is anchored by weathervaning turret mooring system and
features 20 mooring lines each of which are 1. 6 km long.
Through Quad 204, BP
extensively modernized the
subsea systems to increase
capacity and extend field life.