1 MSc in Subsea Engineering EG55F6 Risers Systems and Hydrodynamics Overview of Riser Engineering Dr Patrick O’Brien Honorary Professor of Engineering, University of Aberdeen & Group Director, MCS Kenny MSc in Subsea Engineering Presentation Overview 1. General Concepts & Field Layout 2. Riser System Types 3. Overview of Fundamentals of Riser Engineering 4. Riser Design Considerations EG55F6 Risers Systems and Hydrodynamics
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MSc in Subsea Engineering
EG55F6 Risers Systems and Hydrodynamics
Overview of Riser EngineeringDr Patrick O’BrienHonorary Professor of Engineering, University of Aberdeen & Group Director, MCS Kenny
MSc in Subsea Engineering
Presentation Overview
1. General Concepts & Field Layout
2. Riser System Types
3. Overview of Fundamentals of Riser Engineering
4. Riser Design Considerations
EG55F6 Risers Systems and Hydrodynamics
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MSc in Subsea Engineering
Key Messages
Dry tree vs wet tree: Tensioned vs Compliant
Riser TypesypTTRs, Flexibles, SCRs, Hybrids
Riser FundamentalsLarge displacement, effective tension, equations of motion, time vsfrequency domain
Riser Design ConsiderationsVessel motionsTouchdown response and buckling
EG55F6 Risers Systems and Hydrodynamics
Touchdown response and bucklingFlexible pipe design issues and failure modesSCR design issues: touchdown and top connection flex/stress jointInternal flow regime and insulationCross-section impact on global motionsCoupled vessel-mooring-riser response
MSc in Subsea Engineering
1 G l C t & Fi ld L t1. General Concepts & Field Layout
• Dry Tree vs Wet Tree• Tensioned vs Compliant
EG55F6 Risers Systems and Hydrodynamics
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RESERVOIR CONDITIONS
ENVIRONMENTAL
Riser System Selection
FIELD LAYOUT
SURFACE UNIT
PRODUCTION SCHEME
CONDITIONS
EG55F6 Risers Systems and Hydrodynamics
RISERSYSTEM
MSc in Subsea Engineering
System Architecture: Girassol Subsea
EG55F6 Risers Systems and Hydrodynamics
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Boomvang Nansen Fields
EG55F6 Risers Systems and Hydrodynamics
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Two Main Riser Types“Dry Tree” riser“Wet Tree” riser
Preliminaries:(Christmas) Tree ~ “manifold” type structure
EG55F6 Risers Systems and Hydrodynamics
( ) ypPoint at which reservoir fluid iscontrolled“Head” of the well
Tree at seabed ~ “Wet” TreeTree at sea surface ~ “Dry” Tree
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Feasibility of Dry or Wet Tree...
“A riser should be vertical below wellhead (or Tree)”Tree)
to allow equipment to be transmitted through the well
If Dry tree riser...Riser must be vertical (from surface to seabed)Cannot be connected directly to moving vessel
EG55F6 Risers Systems and Hydrodynamics
Cannot be connected directly to moving vesselIf Wet tree riser...
No need to be vertical (from surface to seabed)Can connect directly to vessel (Slack in Riser)
MSc in Subsea Engineering
Dry vs Wet Tree Fundamentals
How to cope with motions of vessel (Dry)Riser Supported Vertically by buoyancy canspp y y y yRiser connected to vessel by Tensioners
Tensioners (like springs) extend and compressRiser top response decoupled from vessel motions
Vessel Heaves, riser doesn’t
How to cope with motions of vessel (Wet)
EG55F6 Risers Systems and Hydrodynamics
( )Riser connected directly to vesselEnough slack/compliancy built into riser
e.g. use of Wave shape configuration
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Offshore Production Facility Types
EG55F6 Risers Systems and Hydrodynamics
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Floating Production Vessel Types
FPSO
SemiD d ft
Mini TLP
EG55F6 Risers Systems and Hydrodynamics
Deep draft
SPAR
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Independence Hub Semi
World’s deepest risers…2,438m
SCRs – 7 Initial- 9 Future
Umbilicals
EG55F6 Risers Systems and Hydrodynamics
Umbilicals –STU
MSc in Subsea Engineering
Technology Limits: Water Depth
Deepest Semisubmersible (Independence Hub approx 2,440m)( p pp )(Nakika 1,920m)
• Must have dual independent barrier between uncontrolled reservoir fluid and environment
Outer Annulus
Inner Annulus
13 3/8 “ Outer Casing
9 5/8” Inner Casing
5 ½” Production Tubing
– I.e. below wellhead
• Dry Tree– Single or Dual Casing Riser
• (from Seabed to Surface)
EG55F6 Risers Systems and Hydrodynamics
• Wet Tree– No need (below wellhead = below seabed)
MSc in Subsea Engineering
TTR Riser Design Issues
What is the wall thickness of casings?Withstand stresses (hoop axial bending )Withstand stresses (hoop, axial, bending,..)Extreme, fatigue, VIV loading
How many cans/tensioners required to support the risers?
EG55F6 Risers Systems and Hydrodynamics
Tapered sections (reinforcements at seabed and vessel interfaces)
Provides moment transition between flexible and rigid end connection
Design ConsiderationsPolyurethane fatigue and creep
Non-linear material propertiesSteel collar for load transfer
Steep Wave
EG55F6 Risers Systems and Hydrodynamics
Steel collar for load transferInterface arrangement
e.g. I-tubes, porch,Manufacturing tolerances
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Buoyancy Devices
TypesDistributed – lazy wave and steep wave configurations
Configuration achieved by buoyancy modulesManufacturers include
Trelleborg CRP LtdFlotechEmerson Cuming
Concentrated – lazy S and steep S configurationsConfiguration achieved by tether buoy
EG55F6 Risers Systems and Hydrodynamics
g y yManufacturers include
Trelleborg CRP Ltd
MSc in Subsea Engineering
Distributed BuoyancyDistributed
Steep-waveLazy wave Lazy PliantSteepLazy-wavePliant waveFloatation attached to result in desired riser configurationBuoyancy Supplied by discrete modules
Lazy Wave
Pliant Wave®
Steep Wave
EG55F6 Risers Systems and Hydrodynamics
Clamps required for buoyancy module to make connection to pipe
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Distributed Buoyancy
Design considerations– Usually syntactic foam– Net buoyancy requirement
output from configuration design– Clamping
EG55F6 Risers Systems and Hydrodynamics
gModule slippage can alter
configuration– Gradual loss of buoyancy over time– Clashing
MSc in Subsea Engineering
Distributed Buoyancy
Buoyancy Module2 half shellsHeld in place by clampHalf shells strapped together over clampProfiled to avoid overbending of riser
EG55F6 Risers Systems and Hydrodynamics
overbending of riser
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Distributed Buoyancy Issues• Numerical modeling of modules -
discrete or smeared• Accounting for parameters that reduce g p
3 O i f F d t l f3. Overview of Fundamentals ofRiser Engineering
EG55F6 Risers Systems and Hydrodynamics
MSc in Subsea Engineering
Beam Stressesy
x
∫= dAT σ
z
dxdMzVy =
E l B lli B
EG55F6 Risers Systems and Hydrodynamics
∫
∫−= dAyM z σAxial stresses much larger than shearstresses
Euler-Bernoulli Beam:
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Effective Tension
Global EffectsDerive effective tension from apparent weightAdditional hydrodynamic and mechanical loads add to effective tensionBuckling is a function of effective compression (negative effective tension); not true wall compression
Internal Cross-Section EffectsWork with true wall tension and compute true wall
EG55F6 Risers Systems and Hydrodynamics
pstressStress criteria developed from true wall tension and other stressesVon Mises derived from true wall tension
MSc in Subsea Engineering
Riser Large Displacements
EG55F6 Risers Systems and Hydrodynamics
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Convected Axes – Deformed Riser
EG55F6 Risers Systems and Hydrodynamics
MSc in Subsea Engineering
RdKFdKdCdM =+=++
Final Matrix Equations of Motion
~rb~~~~~ −−−−
Mathematically, system of 2nd order linear differential equationsEquations are nonlinear as mass and stiffness matrices are functions of displacement. Nonlinear stiffness includes terms that are a function of stress (effective tension)Rigid body terms accounts for large displacement and rotation
EG55F6 Risers Systems and Hydrodynamics
Solve in Time Domain or Frequency Domain
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Frequency Domain MethodDecompose into 2 equations:
dddDynamic:
Static:
~t
~t
~t
~t FdKdCdM =++
−−−
~rb
~c
~c dKFdK
−−+=
Note: M, C and K assumed time-invariantC t l h t i li it
EG55F6 Risers Systems and Hydrodynamics
Cannot apply where geometric nonlinearity significant in dynamicNote capacity for linearised dynamic aboutnonlinear static
MSc in Subsea Engineering
Frequency Domain Dynamics
~~
ti
~~t
ti
~~t Complexd,F:edd:eFF ωω
0000 −==
Substitute into dynamic equation
ti
~~t
ti
~~t edd:edid ωω ωω 0
20 −==
ti
~
ti
~eFed)KCiM( ωωωω 00
2 =++−
EG55F6 Risers Systems and Hydrodynamics
Solve directly for d0~
Solve matrix equation once for single frequency
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Wave Spectrum Discretisation
Equal area discretisationArea =Sη(ω n )dω = 1
2 a2n
ωn
Sη(ω )
ω, radians/second
Area =Sη(ω n )dω = 12 a2nArea =Sη(ω n )dω = 12 a2n
ωnωn
Sη(ω )Sη(ω )
ω, radians/second
EG55F6 Risers Systems and Hydrodynamics
dω
,
dωdω
,
η ω φ( ) cos( )t a k y ti ni
N
n i= − +=∑
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Fatigue Calculations: Time Domain vs Frequency Domain
Spectrum discretised into finite number of harmonics
Time DomainTime DomainRandom wave synthesised by superposition with random phasesGenerate time-history of wave loading and vessel motionsRun time domain analysis for 3 hour storm (54,000 timesteps)Statistical analysis of output timetraces to calculate fatigue damage
Frequency DomainSolve equations of motion once for each wave spectrum harmonic (50 harmonics)
EG55F6 Risers Systems and Hydrodynamics
harmonic (50 harmonics)Generate response spectrum directlyCalculate fatigue life from properties of response spectrum
• Internal Flow Regime and Insulation• Cross-section impact on global motions• Coupled vessel-mooring-riser response
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Riser Host Vessel Characteristics
1. Host Vessel vs Water Depth2. Host Vessel 6 DoF Motions3. Vessel Motions & Environmental Forces4. Mean Loads & Excursions5. High Frequency Forces & Excursions6. Low Frequency Motions & Excursions7. Host Vessel Motion Data for Riser Design8. Coupled vs Uncoupled Motion Analysis9 H t V l M ti Ch t i ti
3. Flexible Pipe w/ insulationProven design & track record
4. Integrated Production Bundle (IPB)Integrated Gas Lift, heating and services
EG55F6 Risers Systems and Hydrodynamics
g , gEvolving technology – based on flexible pipe
5. Integrated Production Umbilical (IPU)Integrated Gas Lift, heating and servicesEvolving technology – based on SCR
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Riser Concepts (continued)6. Single Leg Hybrid Riser (SLHR) – Single Pipe
With or without wet insulationCombines steel and flexible pipe
7. Single Leg Hybrid Riser (SLHR) – Pipe-in-PipeDry insulation
8. Hybrid Bundle Riser (SLHR)Wet insulated bundle
EG55F6 Risers Systems and Hydrodynamics
9. Top Tensioned Riser (TTR)
MSc in Subsea Engineering
Integrated Production Bundle (1)External Plastic Sheath
Thermal Insulation
Tubes forHot Water or/and Gas Lift
EG55F6 Risers Systems and Hydrodynamics
Flexible Riser Structure
Technip Patent
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Integrated Production Bundle (2)
EG55F6 Risers Systems and Hydrodynamics
Courtesy Technip
MSc in Subsea Engineering
Riser Solutions – Flow Assurance
EG55F6 Risers Systems and Hydrodynamics
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Integrating Riser Design & Flow Assurance
Key items of integrationInsulation and its impact on riser drag-to-weight ratioRiser slugging and its impact on riser dynamics and ultimatelyRiser slugging and its impact on riser dynamics and ultimately fatigue damage
Deep Water Steel Catenary Riser ExampleHow does riser shape influence slugging?How does slugging affect fatigue life?
Methodology of InvestigationPerform slugging analysis with multiphase transient flow assurance software
EG55F6 Risers Systems and Hydrodynamics
Link flow assurance output with riser dynamics software and compute response
Key FindingsSlugging can have significant fatigue damage and depends of type of slugging and inclination of flowline into riser
MSc in Subsea Engineering
Flow Assurance & Riser Dynamics
Riser Insulation:Increases outside diameter of pipe at lower density levels
Drag-to-weight RatioDrag is a destabilising horizontal force and is proportional to riser diameterWeight (in water) is a vertically downward stabilising forceDrag-to-weight (DTW) ratio is a measure of hydrodynamic stabilityRiser values vary from 2m2/tonf to 8 m2/tonf
EG55F6 Risers Systems and Hydrodynamics
Insulation increases the DTW valueLimit on amounts of insulation for catenary risers
Effective Tension is important for buoyant and top tensioned risers
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Flow Assurance & Riser Dynamics
Riser Slugging:Impact of riser shape on sluggingImpact of riser shape on sluggingImpact of riser slugging on riser fatigue
Force terms from:changes in pressure and densitycentripetal due to slug velocity along curved riser
EG55F6 Risers Systems and Hydrodynamics
risercoriolis due to fluid motion in the moving riser frame of reference
MSc in Subsea Engineering
Slugging CharacterisationWADO - Slugging Example - PPL Data
WADO - SCR Touchdown Point Fatigue Enhancements10" Catenary Riser Profile
-1250
-1000
-750
-500
-250
0
TOPSIDES
RISER_1ARISER_1C
RISER_1B
RISER_2RISER_2C
RISER_2B
RISER_3
RISER_3
RISER_3
RISER_3
RISER_2D
RISER_1D
Riser section identification
Force terms computed from fluid pressure and density changes centripetal and
EG55F6 Risers Systems and Hydrodynamics
-2500
-2250
-2000
-1750
-1500
0 250 500 750 1000 1250 1500 1750 2000 2250
Distance from FPSO, m
changes, centripetal and coriolis forces due to slug / riser motions
MSc in Subsea Engineering
Coupled vs Uncoupled Motions•Coupled Motion Analysis (Hydrodynamic coupling)
•(QTFs, wave forces RAOs, current & wind force coefficients, radiation damping & added matrices)•Required if inertia, damping, stiffness of risers & mooring significantly affectRequired if inertia, damping, stiffness of risers & mooring significantly affect response of host facility
EG55F6 Risers Systems and Hydrodynamics
•Uncoupled•RAOs, offsets, sinusoidal drift•Full vessel time history (Spar generally)
Prescribed Motions
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Installation Vessels - SCRs
J-Lay
EG55F6 Risers Systems and Hydrodynamics
Reel Lay
MSc in Subsea EngineeringInstallation, Schedule, Cost Drivers
Steel Riser and FlowlineInstallationS-lay
used up to moderately deep water, modified stinger for very deep waterlimit is curvature induced at stinger
J-laydeep to ultra-deep water riser installation, typically expensive option
Reel-layFaster than J-Lay with more controlled shop (2G - horiz) instead of offshore (5G) welding
EG55F6 Risers Systems and Hydrodynamics
More complex weld testing and fracture mechanics– Large diameter may imply high reeling strains – max strain and low cycle
fatigue challenges– Requires nearby spool base to be economical (WoA challenge)
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MSc in Subsea EngineeringRiser & Flowline System SelectionImpact on Cost and Schedule
Flexible Pipe– Tradeoff = procurement cost vs. installation cost
Steel Flowlines and SCRs– Often lowest procurement cost in deepwater– Deepwater pipelay vessel : J-Lay or reeled lay typical for deepwater
applications, S-Lay for shallow-moderate depth
Riser Towers– Typically most expensive riser installation option
B dl i t ll ti t i ll b t t
EG55F6 Risers Systems and Hydrodynamics
– Bundle installation typically by tow-out– SLHR installation may be pipelay vessel or MODU installation
MSc in Subsea EngineeringInstallation Challenges and VesselCapacity
● Installation ChallengesUltra-deepwater high tension loadsLarge diameterLarge diameterPositioning for TDP & clashing during transferRigging/handling of pull-in/abandonmentWeather fatigue during installationVessel on-site vs. abandonment & recovery (A&R)
Ri F d t lRiser FundamentalsTension / Bending, Effective TensionLarge displacementsTime Domain vs Frequency Domain
Extreme vs FatigueVessel motions
Touchdown bucklingTh l id ti
EG55F6 Risers Systems and Hydrodynamics
Thermal considerationsRiser Design and Flow AssuranceDrag-to-Weight RatioInstallation
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Key Messages
Dry tree vs wet tree: Tensioned vs Compliant
Riser TypesypTTRs, Flexibles, SCRs, Hybrids
Riser FundamentalsLarge displacement, effective tension, equations of motion, time vsfrequency domain
Riser Design ConsiderationsVessel motionsTouchdown response and buckling
EG55F6 Risers Systems and Hydrodynamics
Touchdown response and bucklingFlexible pipe design issues and failure modesSCR design issues: touchdown and top connection flex/stress jointInternal flow regime and insulationCross-section impact on global motionsCoupled vessel-mooring-riser response