Pipeline Design & Installation Systems Rigid pipeline subsea tie-backs – new operational challenges

Paul Georgeson – Operations Support ManagerWood Group Kenny

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- Overview

- Materials

- Inspection

- Monitored data

- Maintenance

and repair

Agenda

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Assets

FlowlinesPipelines

2013-172013-17

820820820820 km

2,400 2,400 2,400 2,400 km

Source: Douglas Westwood

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Areas

Source: Geological Survey of Queensland

Operational regions

- predominantly Carnarvon

basin

- expanding into:

- Browse

- Bonaparte

- possibly Canning and the

Bight

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ChallengesConsiderations for operations

- New depths, cold seawater, hydrates

- Scarp crossings (through, around, over)

- Pipelines passing through new regions

- Design lives > 30 years

- FLNG operating regimes

- Aggressive fluids - CO2, H2S

- High temperatures

Scarp crossing

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Tem

pera

ture

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Materials

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Corrosion

- water (wet gas) + CO2 = carbonic acid (pH 3.8)

- increased temperature and pressure = increased reaction rates

Erosion

- Velocities in excess of 30 m/s

Has led to

- change of materials from carbon steel to a CRA

- chemical injection

- pH stabilisation - change nature of the produced fluid

- corrosion inhibitors - barriers via injected film formers

Material selection - internals

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Lined and clad pipe and spools, various CRA materials primarily 316L, 625, 22cr

Weld materials, can be driven by contractor experience / preference:

- 622 root, 686 fill and cap

- 625

- 309L

- 22 Cr

Design considerations:

- Qualification / historical design temperatures of CRA material

- Overmatching challenge for some nickel weld consumables at high temperature

Corrosion resistant alloys

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Hydrates

- Driving key decisions around external coatings for wet gas flowlines

- Rapid cooling -> hydrates

Wax

- Keep temperatures above wax appearance temperature

Top of line corrosion

- Prevent condensation and water drop out by keeping hot

Has led to

- Keep it hot -> insulated lines, MLPP

- Let it cool -> continuous MEG injection, MEG regeneration plants

Material selection - externals

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Inspection

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Operations – In-line inspection (ILI)

- confirm internal pipeline condition via in-line inspection

- work with regulators / licence requirements

- manage challenges with schedule and plant considerations

such as liquids arrival (flow assurance)

- utilise subsea corrosion / erosion monitor data and

production chemistry data to justify ILI timings

Pre operations

- sample during dewatering for water chemistry and

bacteria / biocide residuals

Corrosion / erosion

Source: Rosen

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Expansion

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Planned buckle ‘design’

- DIs – displacement initiators (dumb or mechanical)

- ZRBs – zero radius bends

Expansion

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Considerations – pre start-up

- Pre start-up inspections, checking for:

- burial around touch down points

- third party interaction

- Possible interventions to remove

seabed material built up around touch

down points

- Recording details of spans either side of

DI

Expansion

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Expansion

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Operations to specify data collection

- global positional data - specifically

buckle shape (x, y, z) survey data

- seabed heights adjacent to pipe and

at set distance from top of pipe

- lateral displacement at DI

- axial movement at DI

- conditions of DI surfaces due to

movement

Expansion

Pipeline crossing DI

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Operations considerations

- global location check campaign to

campaign (drafting, GIS, cloud point

data, etc)

- compare positional data at DI to

operational conditions at the time of

survey / inspection

- run FEA models of buckle shape (x, y, z)

from survey / inspection data – check

stresses and strains

Expansion

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Asymmetry in the expansion / contraction

Drivers:

- Temperature transient

- Seabed slope

- End tension

- Liquid hold up

Axial walking

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Operations to specify data collection

- check location of structure on

foundation - end terminations

designed to move

- check position of spool / flowline

interface flange / connector

- future intervention if required

Axial walking

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Operations

- record complete operational history of start-up / shut downs and link to

structure locations

- understand spool loads based on position of structure (and associated

connector) and location of spool / flowline connector

- model future movements to ensure they remain within design parameters

or plan for any intervention requirements

Axial walking

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Monitored data

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Managing data is key, especially with long design lives

Make systems as automated as possible

- Define integrity operating windows (IOWs)

- Production chemistry

- MEG system + pH stabilisation / corrosion inhibitors

- Water chemistry

- Erosion / corrosion monitoring systems

- Velocities / temperatures / pressures

Regular reporting / dash boards summarising data and asset condition

Data management

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Data recovered from interventions

- monitoring of spans / structures / spools

- collect data for pipelines / riser motions in operations where there are fatigue

concerns

Understand met ocean conditions

- impact of currents, solitons, tides, cyclones on subsea assets

Understand influence of operations on assets

- impact of production regimes, slugging, flow rates on motions / vibrations

Data collection from interventions

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Maintenance and Repair

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Reaching critical mass for:

- formation of a ‘repair club’

- equipment sharing

- tool pool

Still CRA repair challenges

Storage and location of CRA and CS pipe will be important

Smaller pipelines may be as critical as the production system (4 - 8” MEG / Utility lines)

Significantly high pressures in smaller lines, worth spending time considering spares /

repairs options

Pipelines

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- Number of operational challenges which are pushing industry boundaries

- Pre-start up data capture critical to understanding asset baseline condition and

managing future decisions

- Management and analysis of inspection and monitored data will be key in early field

life, ensure all calibration work undertaken (project to ops)

- Legislative framework to be managed

- Longer term larger interventions will be critical and require significant planning

- Challenge to industry to ensure Operators get the support and value required

In summary..