Richard Rickett, General Manager Engineering and Procurement - March 2015

Case Study

Case Study :Diverless Fast Track

Repair of Mooring System

3DOF Subsea

Introduction

• ~ 300 floating production units in use around the world

• Design = maximise uptime = minimise disconnection/reconnection=> need to withstand fairly extreme weather conditions

• Analysis based on historical environmental data• However - weather is inherently unpredictable and expected limits can be exceeded

• Potential early deterioration of mooring system components or at worst, failure of single or multiple mooring lines.

• Very few have facilities to detect early warning signs of deterioration or impending failure

• Regular inspection campaigns carried out to confirm integrity of mooring system

• Not uncommon for the early signs of failure to be detected during routine inspection

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Mooring System Early Failures

• Many single line failures• Several examples of multiple line failures (wire, chain and/or connections)• Major component failures (yoke, wire, chain, connections)• Vessel drift-off• Subsea hardware and risers damaged or broken, catastrophic failure

RegularInspection

Repair prior to failure

Failure

Inspect damage

Repair

Planned $$ Emergency $$$$$

3-6 months

on station / off-station

• Located 80km off the coast of South Taranaki, New Zealand, at the entry to the Cook Strait

• Largest crude oil field in New Zealand• Contributes significantly to the economy and

development of the Taranaki region.

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Case Study - Maari Oil Field

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Maari field consists of :

• Subsea wells, flowlines & control umbilicals• Maari wellhead platform• FPSO Raroa, 8 leg mooring system

Water depth approx. 100m

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Each mooring leg comprises :

• Driven anchor pile• Lower 118mm chain section 50m• Lower 110mm wire section 200m / 400m / 500m• Upper 118mm chain section 400m• Upper 110mm wire section 200m

Chain : 118mm studless linksWire : 110mm spiral strand uncoated wire rope

• In February 2013, a 5-year ABS inspection programme was carried out by DOF Subsea Diving Support Vessel Skandi Singapore

• Survey included an ROV survey of the 8 mooring legs• Bird-caging of spiral strand wire mooring rope was observed on mooring legs 1, 2, 3 & 4• Considered likely to effect the capacity of the mooring legs• Subsequent to the inspection, the Upper Wire Section on mooring leg No. 2 parted• Temporary mooring leg installed in Aug 2013 by others

Mooring wire anomalies

Timeline Feb Mar Apr May June July Aug Sep Oct Nov Dec

Anomalies identified in this area

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Cut & add chain

Cut & reterminate

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• Letter of Intent for engineering signed end July 2013• Procedure and tooling review held early August• Method statement developed, design loads calculated – 65-150 tonnes• Design based on 3m significant wave height limit• Concept developed based on an existing (lower capacity) tool previously accepted by the

classification society :

Existing tool (10t pull capacity) New concept (150t pull capacity)

• Orders for long lead hydraulic parts placed immediately

Engineering of Solution

Feb Mar Apr May June July Aug Sep Oct Nov DecTimeline

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Engineering of Solution

• Fabrication of tool awarded to a New Zealand company (New Plymouth)

• Close to port of mobilisation• Fabrication commenced end Aug 2013• Tool completed in 4 weeks• Load and function testing completed 7 weeks after

contract award)

Fabrication

Feb Mar Apr May June July Aug Sep Oct Nov DecTimeline

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• Built : 2010• Length : 108 m• Beam : 24 m• DP : Class 2• Bollard Pull : 350 t• Chain locker capacity : 1150 m3• Triple drum main winch : 500 t• Heave compensated crane : 140 t• 2 off safe Deck rail cranes : 5t• A-frame : 250 t• Clear Deck Area : 1,070 m2• Accommodation : 90 personnel• ROVs: inbuilt 3,000 m work class ROV + overside

work class ROV (Schilling UHD)

Execution - Skandi Hercules

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• Depth rating : 3,000 m• Power : 150 HP• Payload capacity : 400 kg• Through frame lift : 3,500 kg• Manipulators :

• 7-function Titan T4• 5-function Rigmaster

Execution – Schilling UHD ROVs

Feb Mar Apr May June July Aug Sep Oct Nov Dec

Mobilisation - Skandi Hercules

• Vessel contract signed mid August 2013• Hercules mobilised in Singapore 3 weeks later• Constructability Review held early September• Vessel arrived in New Plymouth NZ end September• Final risk assessment held early October

Timeline

• Identify location for Upper Chain Section cut subsea• Lift chain section into cutting stand• Cut chain with ROV carbide blade cutter

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Repair Methodology

cut location

• Recover FPSO end upper chain section and upper wire section

• Store chain section in vessel chain lockers

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Repair Methodology

• Fit recovery clamp to wire• Recover wire to deck & secure• Cut & remove damaged wire• Clean wire end• Re-terminate with new wire socket

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Repair Methodology

• Reconnect chain to repaired Upper Wire Section• Deploy chain until end is reached• Fit end of chain through ACCD stroking tool skid and secure in place

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Repair Methodology

• Deploy chain and ACCD tool to seabed

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Repair Methodology

• Recover other end of mooring line to deck• Attach new length of chain section• Lay end of chain into ANC ACCD tool• Fit H-link to end of chain

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Repair Methodology

• Deploy chain and ANC ACCD tool to seabed• Connect 20m tether lines between HYD and ANC

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Repair Methodology

• Connect hydraulic downline• Connect crane to chain end• Stroke tool (varied 5- 30m) & recover chain

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Repair Methodology

• Once sufficient slack is pulled through, lower chain end link into H-link• Insert H-link pin• Attach locknut.

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Repair Methodology

• Release load from ANC tool, remove tethers• Slide ACCD tool off carriages• Recover ACCD tool to deck, recover carriages to deck

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Repair Methodology

• Remove pins to release ACCD ANC tool• Lift chain off tool• Recover ACCD ANC tool to deck

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Repair Methodology

All tooling is recovered, leaving only H-links and anchor shackles in the chain leg

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Repair Methodology

Challenges - Range of Weather

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Leg 2 : 7.5d ops + 6.5d WOW, FPSO in place.Leg 3 : 4d ops + 1d WOWLeg 1 : ~4d ops + 1d WOWLeg 4 : 2.5d ops, no weather downtime.

Challenges – Visibility at the Seabed

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Challenges - first leg repaired with FPSO in place

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Jul Aug Sep Oct Nov

2013 Final risk assessment

Constructability Review

Skandi Hercules mobilised in Singapore

Vessel contract signed

Tooling review

Engineering awarded

Engineering

Tool fabrication

Tool testing

Mobilisation in Taranaki, New Zealand

Offshore works 1 month

Performance - Timeline

Complete14/11/2013

Award31/07/2013

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Learning curve‐‐‐‐‐‐‐‐

Performance - Safety

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• 1 non-work related injury (rolled ankle climbing out of bunk while vessel in harbour)• 1 first aid case – small cut to finger while cleaning under shelving• Significant amount of deck work• All work performed without divers

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Key Success Factors

• Proper detailed Engineering assessment

• Competent and experienced team, onshore and offshore

• Preparation – testing, trial fits, site integration tests

• Right assets

Conclusion

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Fast track repair of FPSO mooring legs can be carried out safely and effectively, without the use of divers, and with the FPSO in place.

DOF Subsea wish to recognise and thank OMV New Zealand Limited for permitting the use of the material contained within this presentation.

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Acknowledgements

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Questions ?

Thank you