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Challenges of ‘Deep’ Water To Jackup Conductors And Risers
Alex RimmerEngineering Team Leader, 2H OffshoreSubsea Europe14-15th November 2011
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Overview
What is ‘deep’ water for jackup rigs?Jackup conductor/riser arrangementsWhat are the limitations in ‘deep’ water?How do we overcome the limitations in ‘deep’ water?
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What Is ‘Deep’ Water For Jackup Rigs?
>>80M
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Jackup Conductor/Riser Arrangements
JackupAccess/tensioning deckConductorSurface wellheadSurface casingSurface BOPOvershotDiverterCasingsPull-up tensionerPush-up tensionerTemplateMudline suspension (MLS)Subsea housing/wellheadFull-bore HP drilling riser
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What Are The Limitations In ‘Deep’ Water?
System doesn’t scale well – increased jackup & riser deflectionsLimited ‘deep’ water experience in harsh environmentsHigh pressure typically requires large BOP – very stiff
L
L
BM BM
<<80m >>80m
limit
limit
50 Year Wave + Current
Large jackup motion
Small jackup motion
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Rotary Table
Diverter
Top of Overshot MandrelOvershot PackerOvershot Mandrel
Annular BOP
BOPBOP Adapter
CTU Deck
Tension Joint
Bottom of hull
MSL
Lower Stress Joint
Wellhead Connector
Tree
WellheadTemplate
Mudline
30 x 1.5" Conductor (1st ST2 Connector)
(Bottom of Model)
Tension Ring
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Conductor and Riser Design IssuesConductor/riser joints through tensioner (>1.0 σy, fatigue, >connection capacity)Conductor/riser joints above subsea wellhead (>1.0 σy, fatigue, >connection capacity)Connections to wellhead, tree and BOP (> capacity)Conductor joints below subsea wellhead (>1.0 σy, connection capacity)*Overshot lateral load (~40-60Te)Lateral load on tensioner and/or tension deck (~80-120Te)Overshot rotational lockup (0.5-5deg) induced load
* Generally improved compared with semi-submersible for subsea well with HP riser
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How Do We Overcome The Limitations In ‘Deep’ Water?
Reduce conservatism in analysis methodologies
Riser operational procedures
Design changes to riser and vessel
Integrity Management
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Reduce Analysis Conservatisms
>30% improvement in response achievable
Original
BM
Reduced Conservatism
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Riser Operational ProceduresDe-pressurise (plug/water fill) – improve system capacityDisconnection of overshot mandrel
L
BM
50 Year Wave + Current
Large deflections/rotations
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Design Changes
RiserVIV suppression – strakes, fairingsSecondary tensioner systemsFlanged riser connectionsFlange bolt material grade and preload increaseLocalised wall thickness and material gradeIntegrally forged jointsFlexible overshot mandrel
VesselIncrease rig load capacities
Vertical - cantilever/tension deckLateral - tension deck/overshot
Floating diverter
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Integrity Management
Instrument riserDefine integrity management planDefine key performance indicators (KPI) to assess response against
Green = no action requiredOrange = evaluate responses furtherRed = inform operator
immediately
Determine if measured responses match predicted responses
Validate analysis modelsCalibrate riser models if requiredRedefine KPI’s if required
Rotary Table
Diverter
Top of Overshot MandrelOvershot PackerOvershot Mandrel
Annular BOP
BOPBOP Adapter
CTU Deck
Tension Joint
Bottom of hull
MSL
Lower Stress Joint
Wellhead Connector
Tree
WellheadTemplate
Mudline
30 x 1.5" Conductor (1st ST2 Connector)
(Bottom of Model)
Tension Ring
Upper riser monitoring
strain, rotation, tension
Mid-riser monitoring
lateral motions
Lower riser monitoring
strain, lateral motion
Vessel monitoring
overshot strain, lateral
motion, wave, current
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Conclusions
Conventional jackup conductor and riser arrangements do not scale well to ‘deep’ water (>>80m)
Large dynamic jackup motionsHigh dynamic loading on riserLimited flexibility in riser components
Jackups in depths of ~130m with 7000psi pressures are possible through
Improved analysis methodologiesOperational proceduresDesign changes to riser and vesselIntegrity management of installed riser
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