Copy (2) of 2h Riser Design

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RISER DESIGN

Hugh Howells

2H Offshore Engineering Ltd

Marine Risks Workshop

International Association of Oil & Gas Producers

Sopwell House, St Albans, UK

16th-18th March 2003



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Introduction Riser Design Process

Interfaces Implications of Deep Water

Why things go wrong Technology extension v New

technology

Monitoring



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Deepwater Riser Systems

Production, Export

and Service Risers

Production, ExportProduction, Export

and Service Risersand Service Risers

Steel Catenary

SteelSteel CatenaryCatenary

Free Standing

Free StandingFree Standing

Vertically Tensioned

VerticallyVertically TensionedTensioned

Flexible

FlexibleFlexible

Drilling and

Completion Risers

Drilling andDrilling and

Completion RisersCompletion Risers



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Design ProcessCollate Inputs

Fluid properties, vessel motions,attachment position, extreme and long

term waves and current, soils, fieldlayout,

Analyse

Sizing, storm, clearance, VIV, first andsecond order fatigue, installation

Confirm Details

Fabrication methods, stress concentrations,strakes/fairings, and if necessary:

Re-define Configuration

Wall thickness, top tension, take-offangle, orientation, spacing, vessel

motions



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Interfaces Risers are probably the most interface

intensive component of a deep waterproduction system: Fluid properties - coatings, fatigue

performance

Field layout/flowlines - orientation,spacing, loading

Vessel type and size, motions, attachment

position, loading Mooring pattern

Wellhead/Foundation – loading



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SCR Interfaces



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Top

TensionedRiser

Interfaces



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gComplexity Increases

with DepthTLPTLP Spar Spar

Environmental novelty

Unique vessel characteristics

Steel weight

Tension

Stroke

Deflections

Interface loads

Clashing potential

Process flow

Isolation and safety

Interface complexity

CAPEX



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Why things go wrong Belief that proven technology is being

used Novelty not adequately recognised

Insufficient front end work

Interfaces not clearly defined and

managed

Cross-discipline implications notaddressed



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Implications of Change

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 OK System limits - when does extension

become difficult

Can’t be first mindset

High 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, detailedengineering 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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SLOR

TM

S ingle Line O ffset R iser

Production, Gas Injection

Water Injection

CORTM

C oncentric O ffset R iser

ProductionRiser Base Gas Lift

Active Heating

N2

or Vacuum Insulation



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Single Line Hybrids -

CORTM /SLORTM

Vessel flexibility Field layout flexibility

Process flow flexibility

Pre-installation Less complex than bundle

Threaded construction

Deep and ultra deep solution



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Threaded Connection

Fatigue2H Offshore Fatigue Testing Data

Threaded Riser Flowline (TRF) Phase III Testing

10

100

1000

1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08

Number Of Cycles (N)

S t r e s s R a n g e ( S )

Unfailed Samples With Axial Mean Stress (150Te Tension) Unfailed Samples With Zero Axial Mean Stress

Unfailed 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 Stress

Target DnV B with SCF 2.0 Target DnV B Curve with SCF 3.0

Mean DnV B Curve Mean DnV E Curve



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H 2 S – Effect on Fatigue

Performance Significant reduction in fatigue

performance if H2S present (Factor of 20

on life at 60deg C)



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Drilling - Current Practice Use an 18-3/4in ‘sledgehammer’ to drill a big

hole from an expensive vessel - high costwell !!

Why hasn’t this approach changed ? Standard practice - conservatism

High investment in BOP hardware

Rig contracting strategies Slow development of better casing programs



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Height = 14.5mWeight = 250Te



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Deck Space & Top Tension



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Small Bore Riser

For Deep Water Small bore lightweight riser (13-16in)

High pressure with surface BOP Subsea Shut Off Device (SSOD)

Efficient casing program

Slim, slender or expanded



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HP D illi Ri i h SSOD



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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 2annular BOPs

•One Blind Shear Ram





Benefits of Small Bore

Approach Reduced riser tension and buoyancy volume

Reduced riser and BOP cost

Reduced deck load and storage area

Faster riser installation and retrieval (x10)

Eliminate kill, choke and booster linecomplexity

Improved cutting transport

Faster drilling (reduced hole size)

Reduced consumables

Reduced cuttings

Better well control

Improved BOP maintenance




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Spar for

HP Risers or Large Depths




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TM

HP Drilling Riser HP Drilling Riser

Surface BOPSurface BOP

SubseaSubsea wellheadswellheads

Horizontal TreesHorizontal Trees

ManifoldManifold

Free standing RisersFree standing RisersSLOR/CORSLOR/COR

A deep and ultra deep solutionA deep and ultra deep solutionSemi ProductionSemi Production

PlatformPlatform

TM




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Summary of Features

True deepwater solution Riser & well system focus

Vessel independent

Simplified interfaces

Proven technology

Depth insensitive – ultra deep

application

Fast track schedule and start up





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Monitoring for Novel

Systems Objectives

Confirm response predictions Determine margin in design and

confidence in long term performance

Confirm need for ongoing monitoring Keep Costs Down

Be selective

Low cost devices

O /





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Observed /Predicted

ResponseSCHIEHALLION SHEAR7 COMPARISON

All 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 1

Mean Current Speed (m/s)

O

b s / P r e d i c t e d S t r e s s R a t i o




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SCHIEHALLION SHEAR 7 COMPARISON

All Logged Events - Sheared Profile Comparison

0

5000

10000

15000

20000

25000

30000

35000

40000

0 0 0 1

0 0 5 1

0 1 0 1

0 1 5 1

0 2 0 1

0 2 5 1

0 3 0 1

0 3 5 1

0 4 0 1

0 4 5 1

0 5 0 1

0 5 5 1

0 6 0 1

0 6 5 1

0 7 0 1

0 7 5 1

0 8 0 1

0 8 5 1

0 9 0 1

0 9 5 1

1 0 0 1

1 0 5 1

1 1 0 1

Event No.

C u m u l a t i v e D a m

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Observed Cumulative Damage Predicted Cumulative Damage (Cut-Off=0.4)




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Use experienced people to identify novelty

and its effects

Adopt multi-discipline approach to FEED

Appreciate each others challenges

Enable early changes in related disciplines

Simplify interfaces / maintain flexibility

Extension of existing technology may be

more challenging than proving of new

technology/systems

Use monitoring of novel systems to prove

design assumptions and predictions

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