innovative riser configurations for ultra shallow water - … · innovative riser configurations...

Innovative Riser Configurations for

Ultra Shallow Water

Emad Libis, NOV FlexiblesClaus Dencker Christensen, NOV Flexibles

February 26, 2015

Agenda

�Intro�Motivation�Typical Challenges in Ultra Shallow Water�A Robust Solution�Validation�Further Enhancements�Summary and Conclusion

Slide 2

AOG • Innovative Riser Configurations for Shallow Water • Claus Dencker Christensen • Emad Libis

©2014 NOV | Proprietary and confidential. 3

FLEXIBLE RISERS, INTRO

� Intro� Motivation� Typical Challenges in Ultra Shallow Water� A Robust Solution� Validation� Further Enhancements� Summary and Conclusion

Intro, Biography

Emad Libis� MSc Structural Engineering 2012� National Oilwell Varco 2012 - Date

Pipe System Design EngineerExchange member, Specialist & Sales Unit

Main engineer, Asia-Pacific, System Design

Slide 4


Claus Dencker Christensen� MSc, PhD Structural and

Hydraulic Engineering 1996� Offshore Technology, DHI 1996 - 2006� National Oilwell Varco 2006 - Date

Technical Authority, System DesignPrincipal Engineer, System DesignLeads NOV Specialist & Sales Engineering Unit

Involved in all NOV Asia-Pacific projects since 2007

Intro, Flexible Risers

Pipe Designs:

Slide 5


Basic Configurations:


MOTIVATION


Motivation� Most easy accessible oil/gas reserves exhausted� Trunklines expensive for new fields� FPSO becomes economically preferable� Un-bonded flexible risers absorb FPSO motion� Most challenging new development:

� Extreme water depth (>1000 m)� Rough environment ultra shallow water (<<100 m)

Slide 7


Motivation, Typical Riser SystemsFlexible riser systems, examples:

Slide 8


Fixed-S ->Ichthys->

D=280m

TGT->

D=43m

Riser Turret Column -> Bal naves ->

D=79m

Okha->

D=79m

Lazy-S ->

Ichthys->

D=280m

Troll B,

Åsgaard B->

D=350m

Li vorno->

D=112m

Western Is l es->

D=160m

KMZ *4->

D=90m

Dai Hung->

D=111m

Alba->

D=140m

Gryphon->

D=112m

Ettri ck->

D=111m

Maari->

D=104m

Pierce->

D=85m D1 Fiel d->

D=91m

PM-3->

D=62m

Su Tu Vang->

D=54m

Orki d Pakma->

D=58m

Curl ew->

D=91m

Steep Wave ->Hadera->

D=73m

Dumbarton->

D=120m

Martin Li nge->

D=118m

Gryphon->

D=112m

Ettri ck->

D=111mWenchang->

D=125m

Enpi ng->

D=85m

Xi ji ang->

D=91m

Mariner->

D=109m

Rang Dong->

D=60m

Montara->

D=77m

Tethered Wave ->Visund, Njord,

Snorre,etc->

D=330m

Alba->

D=140m

Martin Li nge->

D=118m

Affl eck *1->

D=79m

Brunhi lde *2->

D=85m

Curl ew *3->

D=91m

Lazy Wave -> Kakap->

D=90m

Free Hanging Catenary -> Snorre A->

D=350m

Madura->

D=55m

Wave Height/Water Depth -> [%] 10% 12.50% 18% 25% 33% 50%

*1: Semi-sub, max. 14m offset

*2: Neighbour for Pierce

*3: Heavy Uraduct necessary (Lead), Turret at 80% vessel length, Max. 7" Riser

*4: Steep-S

Sy

ste

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om

ple

xit

y/P

rice

Environment Severity


TYPICAL CHALLENGES

� Motivation� Typical Challenges in Ultra Shallow Water� A Robust Solution� Validation� Further Enhancements� Summary and Conclusion

Typical Challenges 1:3

� Vessel “Far” position: Risers stretched

� Vessel “Near” position: Hogbend–Vessel InterferenceSagbend-Seabed InterferenceOverbending Sagbend

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Typical Challenges 2:3� Transverse environment: Interference with mooring or buoyancy

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� High Downwards Vertical Velocity: Riser snatch over-bending under turret

Typical Challenges 3:3� Large motion of Hogbend/MWA: Overbending touchdown/hog-bend

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SOLUTION

� Intro� Motivation� Typical Challenges in Ultra Shallow Water� A Robust Solution

Study Case, Step-By-Step1) Basic System Selection (Interference, Touchdown)2) Riser Stiffness Cover (Over-bending Sagbend, BS, Touchdown)3) Restricted-S (Increase Pliancy of Stretched Riser)

� Validation� Further Enhancements� Summary and Conclusion

Solution, Study Case

Example: Most extreme shallow water system known => Wave Height / Depth = 0.42

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Variable Value Water Depth ~43 m Max. Wave Height ~18 m Max. Current Velocity ~2 m/s Number of Risers 7 in one mooring sector Number of Umbilicals 1 in same mooring sector Max. Riser ID ~9” Vessel Type Weathervaning FPSO, Size: Aframax Vessel Draft Range ~7 m -14 m Mooring type Bow-mounted Turret Mooring System 3 x 4 groups mooring legs Max. Vessel Offset (Downstream) ~19 m Max. Vessel Offset (Upstream*) ~5 m


Solution, Rejected Systems 1:2Failed solution attempts: Camel Back (Double Wave) , Tethered Wave (Single Wave)

Slide 15


Start of lifeStart of life

WaterfilledWaterfilled

EmptyEmpty

End of lifeEnd of life

WaterfilledWaterfilled

EmptyEmpty

Solution, Rejected Systems 2:2Decent solution attempt:Lazy-S (MWA Buoy)

Slide 16


� Deep water: Risers control (move) MWA Buoy� Shallow water: MWA Buoy controls (moves) risers

MWA Buoy sometimes move opposite FPSO� Therefore: Advantage if MWA Buoy does not move

Solution, Basic System Slide 17

Fixed-S with heavy risers selected:� Helps control interference with vessel� Helps control interference with mooring� Less bending of risers� No buoyancy module interference


Maximize pliancy of the configuration:� Minimise distance from structure to the turret centreline� Maximise height of structure

Solution, Restricted -SSlide 18

TurretCL

TurretCL


Solution, Restricted -STo gain enough system pliancy:� Place MWA top high in the ”Vessel Exclusion Zone”� Restricted-S is feasible and robust

Slide 19


Solution, Riser Stiffness CoverControl Overbending of Flexibles:� Use ” Riser Stiffness Cover” to avoid over-bending

Slide 20

Parameter 9” Riser 9” Riser With RSC MBR Storage [m] 2.66 2.66 Bending Stiffness at 20°C [kNm2] 160 445

Riser Stiffness Cover is an extruded layer typically made from a very robust, durable and stiff polymer. Typically:

HDPE Grade 100


Solution, HDPE G100 StatusTested and Proven:

Fatigue Notch Sensitivity

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Materiale Temperatur,°C

23 0 -20 -40

HDPE 28 kJ/m2 24 kJ/m2 25 kJ/m2 26 kJ/m2

MDPE 18 kJ/m2 15 kJ/m2 10 kJ/m2 3 kJ/m2

PA11 87 kJ/m2 100 kJ/m2 5 kJ/m2 5 kJ/m2

Solution, Seabed Guide Structure� Avoid damaging risers by contact� Reduce forces on interfacing structures

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VALIDATION


Validation, Main ResultsMain Results, Examples:

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Validation, ExternalSlide 25


�Physical model tests by client�Full independent dynamic analysis by MCSK, Australia�3rd Party Verification, Bureau Veritas / ABS


FURTHER ENHANCEMENT


Further Enhancement� Restricted-S solved this challenge� Even bigger challenges requires new solutions:

Reverse Hang-off :

Slide 27


Sliding-S:

Further EnhancementSliding-S Animation

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SUMMERY AND CONCLUSION


Summary and ConclusionExamples of challenges in ultra shallow water has been demonstrated.

� A robust Restricted-S solution has been presented� Solution validated with physical model tests� Further enhancements to the solution presented� Riser Stiffness Cover is essential

Slide 30


Examples: Riser Stiffness Cover

Thank you for your attention.

Questions?

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