Development of a New Deep-Water Riser Systempossibility.no/utc2008/ps/B3 - Development of a new...

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Development of a New Deep-Water Riser System

Daniel KarunakaranSubsea 7

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IntroductionGrouped SLORTM is an ‘open bundle’ riser solution developed by Subsea 7 and 2H Offshore

Array of close standing SLOR’s/COR’s connected together by a buoyant guide frame

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Single Line Offset Riser - SLORTM

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ExxonMobil Kizomba A & B SLORTM

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SLORTM and CORTM DesignSLORTM and CORTM

Excellant fatigue performance

Decoupled from vessel motion

Pre-installable

Low vessel

payload

Gas lift capability

Field proven

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Multiple single SLORTM

• Spacing

• Clash avoidance - flexibles

• Wake interference of air cans

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Grouped SLORTM Design

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Grouped SLORTM DesignRiser and air can

- Single line or pipe-in-pipe

- Slender air can

Guide Frame- Light weight truss with

buoyancy tanks

- Tethered to suction pile

- Integral receptacles with bearing pads

GUIDE FRAME

CENTRAL FLANGED CONECTION

TETHER

BUOYANCY TANK

SLOR STEM RECEPTACLE

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Grouped SLORTM - ConfigurationTypical 4 SLOR’s/COR’s

- 5 to 6m air can diameter

- 10 to 25m air can length with compartments

- 100 to 150Te base tension

- 50Te tether base tension

- Suction pile foundations

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Grouped SLORTM Design Development• Pipe sizing

• Air can sizing

• Optimization - F/L routing Vessel interface Clearance

• Stability / splay optimization

• Storm / fatigue analysis

• Special joint / forging design

• Installation planning

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Grouped SLORTM - QualificationFinite Element Analysis (FEA)

- Assumed CD of 2.0

- Frame Offset < 2% water depth for deep water (800m), <6% for ultra-deep water (2000m)

- Guide frame typically 150m away from vessel

- Frame bearing loads <10Te, well within capacity of bearing pads

- Riser stroke < 4m

690

700

710

720

730

740

750

-30 -20 -10 0 10 20 30

Distance from Frame Centreline (m)

Elev

atio

n fr

om M

udlin

e (m

)

SLOR Frame

No Current

CD=2.0100yr Current

CD=10100yr Current

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Grouped SLORTM - QualificationComputational Fluid Dynamics (CFD)

- Confirm hydrodynamic coefficients employed in FEA

- Drag coefficient (CD) < 2.0

- Air can spacing of 1.0 diameter gives best response in terms of VIV, wake effects and galloping

- CFD further verified using model tow test

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Grouped SLORTM - QualificationTow Model Test

- Conducted in MARIN’s test centre in Holland

- Model towed at speeds up to 0.7m/s

- Incidence of model to flow is varied

- Air can separation increased from 0.5D – 2.0D

- CD ~ 1.0 to 1.5 for air can spacing of 1.0 time diameter

- No possibility of clashing between air cans

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Full Grouped SLORTM Model Test•MARIN (in Netherlands) was engaged to conduct the model test of Grouped SLOR involving for a water depth of 800m

•Model scaling of 1:73 is adopted

•Model test results gathered should be applicable for deeper water depth

•Results indicate VIV response of risers in Grouped SLOR is smaller than single SLOR

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Grouped SLORTM – Installation AssessmentInstallation of Guide Frame

Installation of Riser- Towing : Tug boats- Reel-lay vessel : Seven

Oceans- J-Lay vessel : Seven Seas

Mating of SLOR/COR with Guide Frame

Installation of Flexible Jumper

Seven Oceans

Seven Seas

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Grouped SLORTM – Installation AssessmentRiser Installation by J-Lay

- Subsea 7 Vessel – Seven Seas

- Assembling of double joints

- Lower riser components via the moon pool using the A&R wire

- Cross-haul operation to transfer riser to main crane and auxiliary crane for connecting riser bottom assembly

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Conclusions•Well developed riser solution for deep and ultra-deep water environments.

•Concepts are qualified

•Eliminate clearance issue with good fatigue performance.

•Installation flexibility.

•High usage of local content.

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Contact Information:

Daniel Karunakaran,Subsea 7

Daniel.Karunakaran@subsea7.com