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Exploring Variety

Why analyze Conductors & Risers?

Determine an operating condition or envelope

• Tension
• Weather limits

Design or select components

• Guide reactions
• High pressure risers
• Connectors & couplings

Determine a need

• Should vortex suppression strakes be fitted?
• How many centralisers are necessary?
• Should we plan for disconnection?

Reduce risk or uncertainty

• Safety critical - Mission critical

Where optimisation might save time or money offshore

• Limiting jackup offset
• Running a template
• Reduce the conductor size or grade

In difficult environments

• High currents off Trinidad
• 30 metre waves in the North Sea
• At the limit of jackup water depth

Novel configurations

Good engineering practice

Code compliance – “fit for purpose”

Certifying authority or government regulation

We don't just analyze the pipe - we look at the whole SYSTEM

Categorize! Where are ‘Risers’ used?

Types of Well

• Exploration
• Tieback
• Platform-Drilled
• Subsea

Activity

• Drilling
• Production
• Side-track
• Slot recovery
• Work-over
• Abandonment

Methods of producing from a well

• Conventional fixed structure
• Minimum weight structure (e.g. monotower, RACP)
• Compliant tower
• Jackup (MOPU)
• Floating vessel (FPSO or Semi-sub)
• Subsea (tied back by flowline to nearby facility)

Tools to drill, workover or abandon a well

• Drilling unit on platform
• Jackup (MODU)
• Floating vessel: Semi-sub, Drill ship

Combinations = endless possibilities

In all of the cases above, conductors or risers will be needed – and may need to be analysed.

What ‘Risers’ are we interested in?

What Wells Can Be Analysed? All wells, new or old can be analysed It all depends on what you want to find out

"Seabed to surface"

What exactly is a 'Conductor'
• ‘Conductor’ is short for ‘Well Conductor’
• It’s a tube…
• This connects an offshore well…
• With the means to work on it or use it. E.g. drilling, production, workover.
• A conductor is a STRUCTURAL element which transfers loads into the SEABED.

What exactly is a 'Riser'?
• A riser is a STRUCTURAL element which connects a well to surface, and may also have to withstand pressure
• Risers are usually, but not always, ‘single string’
• Some configurations have both a conductor and a riser present… (e.g. a subsea well)

Types of analysis – risers & conductors

Static & dynamic structural analysis

• Extreme event: storm loads
• Non-linear: radial gaps, soil springs
• Strength & stability
Vortex induced vibration (VIV) review
• Likelihood of VIV
• Need strakes?
• Fatigue damage

Fatigue assessment

• Wave
• VIV
• Driving Fatigue damage > Life

Thermal analysis

• Wellhead growth
• Casing loads & pre-tensions
• Hanger lift-off

Special types of analysis

• Trawl-board snagging
• Ship impact
• Docking pile assessment
• Under-balanced drilling
• Tree motion
• Platform installation tolerance
• ‘Splitter’ wells (multiple completions)
• High pressure surface risers: Drilling BOPs, Coiled tubing Injector, Hydraulic workover units
• Cement level sensitivity
• Corrosion sensitivity
• Flowline stress
• Casing helical buckling

Types of analysis – other tubular goods
• Platform production risers, caissons, J-tubes
• Pipelines, flowlines, expansion spools
• Renewable energy - e.g. related to foundation piling

Types of analysis – Structures
• RACPs i.e. Rig Assembled Conductor Platforms or Fixed Wellhead Platforms
• Templates
• Subsea protection structures
• Lifting frames & other temporary installation structures

Required Input Data: Standard

Rig/platform Data

• Water Depth
• Deck and Guide Elevations
• Surface Equipment Weights
• Interface Between Rig and Platform

Environmental Data

• Wave Height
• Wave Period
• Current Profile
• Corrosion Limits
• Marine Growth

Casing and Tubing Data

• Pipe Diameters
• Weight
• Grade
• Casing Tensions
• Setting Depths

Connector Data

• Type
• Capacities (Axial + Bending)