balder gulf mexico

Subsea installation in
extreme water depths
– a contractor’s view
Kees van Zandwijk
Heerema Marine Contractors SE
1
Objective of the paper
ƒ Explore when steel wires are better for
deepwater lowering and when fiber ropes
ƒ Vary
– vessel type: crane vessel, OSV
– object lowered: suction pile, template
– sea conditions: Gulf of Mexico, Norway,
Angola
2
Historical development of DWL
ƒ 1990 - 1995
Tension leg platforms
<500t / 1000m
Crane vessels
ƒ 1995 - 2005
Floating production facilities
<500t / 2000m
DWL systems
ƒ 2005 - today
Subsea production units
2000t? / 3000m?
New DWL investments?
3
Reach deeper at less capacity
T
T
T
h
2h
Wire length = 2 x 6 x h = 12h
Capacity = 2 x 6 x Twire = 12Twire
T
Wire length = 2 x 3 x 2h = 12h
Capacity = 2 x 3 x Twire = 6Twire
4
Traction winch for steel wires
F = 60 T
traction winch
F = B * eμα
B = 3 T
storage reel
gas spring
5
Capacity of steel wires vs. depth
Effectiveness [%]
0
0
20
40
60
80
100
‐500
‐1000
Water depth [m]
‐1500
steel wires
fiber ropes
‐2000
‐2500
‐3000
‐3500
‐4000
6
Traction winch for fiber ropes
7
CAPEX of DWL system
CAPEX steel wire vs. fiber rope
steel wires
fiber ropes
0
1000
2000
3000
4000
Water depth [m]
8
Fiber ropes enable use of OSV
Steel wire DWL system
Fiber rope DWL system
1500t
500t
500t
500t
9
OPEX to consider three aspects
Day rate of installation vessel x Net duration of activity
OPEX = Operability of activity
10
Balder installing suction piles
11
Deepwater lowering
1. Over-boarding
2. Passing the waterline
3. Lowering to depth
4. Landing on the seabed
12
LiftDyn analysis of operability
Balder
with
suction pile
OSV
with
suction pile
Balder
with
template
150t
150t
1700t
0m
1000m
2000m
3000m
Structure landing speed < 0.5 m/s
13
Three typical wave spectra
Norwegian Sea
Aasta Hansteen
West of Africa
Angola Block 31
Tp [s]
Tp [s]
Tp [s]
Hs [m]
Gulf of Mexico
Perdido
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Hs [m]
Determine operability
versus wave spectra
Gulf of Mexico
Perdido
Norwegian Sea
Aasta Hansteen
West of Africa
Angola Block 31
Non‐
operable
Non‐
operable
Non‐
operable
Operable
Operable
Operable
Tp [s]
Tp [s]
Tp [s]
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Operability Balder on suction pile
No Active Heave Compensation
16
Operability OSV on suction pile
No Active Heave Compensation
17
Operability OSV on suction pile
With Active Heave Compensation
18
Operability Balder on template
No Active Heave Compensation
19
Elastic stretcher
ƒ Nylon versus fiber rope:
– Nylon strength 3x weaker Æ 3x more A
– Elasticity of nylon 30x lower Æ 30x lower E
– Æ k = EA/L of nylon 10x lower than fiber rope
ƒ Nylon stretcher of 100m has same effect
as 1000m fiber rope
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Operability Balder on template
No Active Heave Compensation
100m nylon
stretcher
200m nylon
stretcher
300m nylon
stretcher
21
Conclusions [1]
ƒ Crane vessels do very well using steel
wires. In specific situations, an elastic
stretcher of limited length may enhance
the operability.
ƒ An OSV installing a suction pile has a
reasonable operability only when using
fiber ropes and active heave
compensation
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Conclusions [2]
ƒ An investment in a steel wire or fiber rope
DWL system should consider:
– type of installation activities (also non-DWL
activities)
– water depth of operation
– wave regime
– installation vessel
Sometimes fiber ropes are better,
sometimes steel wires
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Contact information
Kees van Zandwijk
[email protected]
Radboud van Dijk
[email protected]
Eelco Harmsen
[email protected]
Heerema Marine Contractors SE
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