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RISER DESIGN

Hugh Howells2H Offshore Engineering Ltd

Marine Risks Workshop

International Association of Oil & Gas ProducersSopwell House, St Albans, UK

16th-18th March 2003

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Riser Design ProcessInterfacesImplications of Deep WaterWhy things go wrongTechnology extension v New technologyMonitoring

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ring Deepwater Riser Systems

Production, Export and Service RisersProduction, Export Production, Export and Service Risersand Service Risers

Steel CatenarySteelSteel CatenaryCatenary

Free StandingFree StandingFree Standing

Vertically TensionedVerticallyVertically TensionedTensioned

FlexibleFlexibleFlexible

Drilling and Completion Risers

Drilling and Drilling and Completion RisersCompletion Risers

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Collate InputsFluid properties, vessel motions,

attachment position, extreme and long term waves and current, soils, field

layout,

AnalyseSizing, storm, clearance, VIV, first and

second order fatigue, installation

Confirm DetailsFabrication methods, stress concentrations,

strakes/fairings, and if necessary:

Re-define ConfigurationWall thickness, top tension, take-off angle, orientation, spacing, vessel motionsLearn more at www.2hoffshore.com

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ring Interfaces

Risers are probably the most interface intensive component of a deep water production system:

Fluid properties - coatings, fatigue performanceField layout/flowlines - orientation, spacing, loadingVessel type and size, motions, attachment position, loadingMooring patternWellhead/Foundation – loading

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ring SCR Interfaces

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Top Tensioned

Riser Interfaces

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Complexity Increaseswith Depth

TLPTLP SparSpar

Environmental noveltyUnique vessel characteristicsSteel weight TensionStrokeDeflectionsInterface loads Clashing potentialProcess flowIsolation and safetyInterface complexityCAPEX

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Belief that proven technology is being usedNovelty not adequately recognisedInsufficient front end workInterfaces not clearly defined and managedCross-discipline implications not addressed

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Cost of Change

Extent of Change

FEED Detailed Design In Service

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Evolution of Technology - Issues

Its been used before, therefore its OKSystem limits - when does extension become difficultCan’t be first mindsetHigh price of new technology

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New Technology for Deepwater

SLOR and COR production and export risers

Threaded risers and flowlines

High pressure SBOP drilling risers

STORM production system

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SCR’s - Established Technology?

Offshore Magazine, February 2003 -Referring to SCR’s on Shell Bonga

“Bonga is also extending frontiers, as the region’s first development incorporating steel catenary risers. However, detailed engineering revealed phenomena previously unknown in the industry with unavoidably high rectification costs.”

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Free Standing Risers – Relatively Novel

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Single Line Offset Riser

Production, Gas InjectionWater Injection

CORTMConcentric Offset Riser

ProductionRiser Base Gas LiftActive HeatingN2 or Vacuum Insulation

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Single Line Hybrids -CORTM/SLORTM

Vessel flexibilityField layout flexibilityProcess flow flexibilityPre-installationLess complex than bundleThreaded constructionDeep and ultra deep solution

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Learn more at www.2hoffshore.com

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Threaded Connection Fatigue

2H Offshore Fatigue Testing DataThreaded Riser Flowline (TRF) Phase III Testing

10

100

1000

1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08Number Of Cycles (N)

Stre

ss R

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(S)

Unfailed Samples With Axial Mean Stress (150Te Tension) Unfailed Samples With Zero Axial Mean StressUnfailed Re-Test Samples With Zero Mean Stress Failed Samples With Axial Mean Stress (150Te Tension)Failed Re-Test Samples With Axial Mean Stress (150Te Tension) Failed Re-Test Samples With Zero Mean StressTarget DnV B with SCF 2.0 Target DnV B Curve with SCF 3.0Mean DnV B Curve Mean DnV E Curve

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H2S – Effect on Fatigue Performance

Significant reduction in fatigue performance if H2S present (Factor of 20 on life at 60deg C)

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Use an 18-3/4in ‘sledgehammer’ to drill a big hole from an expensive vessel - high cost well !!

Why hasn’t this approach changed ?Standard practice - conservatismHigh investment in BOP hardwareRig contracting strategiesSlow development of better casing programs

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Height = 14.5mWeight = 250Te

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ring Deck Space & Top Tension

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Small Bore Riser For Deep Water

Small bore lightweight riser (13-16in)High pressure with surface BOPSubsea Shut Off Device (SSOD)Efficient casing program

Slim, slender or expanded

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HP Drilling Riser with SSOD

•13-5/8in Surface BOP with 4 rams and 1 annular

•13-5/8in SSOD with one ram

DP Drilling Vessel

•One Blind Shear Ram

•18-3/4in subsea BOP with 4 rams and 2 annular BOPs

•One Blind Shear Ram

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Benefits of Small Bore Approach

Reduced riser tension and buoyancy volumeReduced riser and BOP costReduced deck load and storage areaFaster riser installation and retrieval (x10)Eliminate kill, choke and booster line complexityImproved cutting transportFaster drilling (reduced hole size)Reduced consumablesReduced cuttingsBetter well controlImproved BOP maintenance

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Spar forHP Risers or

Large Depths

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TM

HP Drilling RiserHP Drilling RiserSurface BOPSurface BOP

SubseaSubsea wellheadswellheadsHorizontal TreesHorizontal TreesManifoldManifold

Free standing RisersFree standing RisersSLOR/CORSLOR/COR

A deep and ultra deep solutionA deep and ultra deep solutionSemi Production Semi Production PlatformPlatform

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stormTMSummary of Features

True deepwater solutionRiser & well system focusVessel independentSimplified interfacesProven technologyDepth insensitive – ultra deep applicationFast track schedule and start up

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Monitoring for Novel Systems

ObjectivesConfirm response predictionsDetermine margin in design and confidence in long term performanceConfirm need for ongoing monitoring

Keep Costs DownBe selectiveLow cost devices

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Observed /PredictedResponse

SCHIEHALLION SHEAR7 COMPARISONAll Logged Events - QC'd Sheared Current Profile

Stress Ratio Current Speed Comparison

0.01

0.1

1

10

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Mean Current Speed (m/s)

Obs

/Pre

dict

ed S

tres

s R

atio

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SCHIEHALLION SHEAR 7 COMPARISONAll Logged Events - Sheared Profile Comparison

0

5000

10000

15000

20000

25000

30000

35000

40000

0001

0051

0101

0151

0201

0251

0301

0351

0401

0451

0501

0551

0601

0651

0701

0751

0801

0851

0901

0951

1001

1051

1101

Event No.

Cum

ulat

ive

Dam

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Observed Cumulative Damage Predicted Cumulative Damage (Cut-Off=0.4)Learn more at www.2hoffshore.com

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ring Low Cost Monitoring Device

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ring Targets for Risk Reduction

Use experienced people to identify novelty and its effectsAdopt multi-discipline approach to FEED

Appreciate each others challengesEnable early changes in related disciplines

Simplify interfaces / maintain flexibility Extension of existing technology may be more challenging than proving of new technology/systemsUse monitoring of novel systems to prove design assumptions and predictions

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RISER DESIGNHugh Howells2H Offshore Engineering LtdIntroductionDeepwater Riser SystemsDesign ProcessInterfacesSCR InterfacesTop Tensioned Riser InterfacesComplexity Increaseswith DepthWhy things go wrongImplications of ChangeEvolution of Technology - IssuesNew Technology for DeepwaterSCR’s - Established Technology?Free Standing Risers – Relatively NovelSingle Line Hybrids - CORTM/SLORTMThreaded Connection FatigueH2S – Effect on Fatigue PerformanceDrilling - Current PracticeDeck Space & Top TensionSmall Bore Riser For Deep WaterHP Drilling Riser with SSODBenefits of Small Bore ApproachSpar for HP Risers orLarge DepthsstormTMstormTM Summary of FeaturesMonitoring for Novel SystemsObserved /PredictedResponseConfirm Fatigue DamageLow Cost Monitoring DeviceTargets for Risk Reduction