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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 Explore when steel wires are better for deepwater lowering and when fiber ropes Vary – vessel type: crane vessel, OSV – object lowered: suction pile, template – sea conditions: Gulf of Mexico, Norway, Angola 2 Historical development of DWL 1990 - 1995 Tension leg platforms <500t / 1000m Crane vessels 1995 - 2005 Floating production facilities <500t / 2000m DWL systems 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 14 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] 15 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 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 Nylon stretcher of 100m has same effect as 1000m fiber rope 20 Operability Balder on template No Active Heave Compensation 100m nylon stretcher 200m nylon stretcher 300m nylon stretcher 21 Conclusions [1] Crane vessels do very well using steel wires. In specific situations, an elastic stretcher of limited length may enhance the operability. An OSV installing a suction pile has a reasonable operability only when using fiber ropes and active heave compensation 22 Conclusions [2] 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 23 Contact information Kees van Zandwijk cvanzandwijk@hmc-heerema.com Radboud van Dijk rvandijk@hmc-heerema.com Eelco Harmsen eharmsen@hmc-heerema.com Heerema Marine Contractors SE 24
