Richard Rickett, General Manager Engineering and Procurement - March 2015 Case Study
Case Study : Diverless Fast Track Repair of Mooring System
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 DOF Subsea 3
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 Planned $$ Emergency $$$$$ Regular Inspection Repair prior to failure Failure Inspect damage Repair 3-6 months on station / off-station DOF Subsea 4
Case Study - Maari Oil Field 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. DOF Subsea 5
Maari field consists of : Subsea wells, flowlines & control umbilicals Maari wellhead platform FPSO Raroa, 8 leg mooring system Water depth approx. 100m DOF Subsea 6
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 links Wire : 110mm spiral strand uncoated wire rope DOF Subsea 7
Mooring wire anomalies 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 Timeline Feb Mar Apr May June July Aug Sep Oct Nov Dec
Anomalies identified in this area Cut & add chain Cut & reterminate DOF Subsea 9
Engineering of Solution 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 Timeline Feb Mar Apr May June July Aug Sep Oct Nov Dec 10
Engineering of Solution DOF Subsea 11
Fabrication 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) Timeline Feb Mar Apr May June July Aug Sep Oct Nov Dec
Execution - Skandi Hercules 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) DOF Subsea 13
Execution Schilling UHD ROVs 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 DOF Subsea 14
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 Feb Mar Apr May June July Aug Sep Oct Nov Dec
Repair Methodology Identify location for Upper Chain Section cut subsea Lift chain section into cutting stand Cut chain with ROV carbide blade cutter cut location DOF Subsea 16
Repair Methodology Recover FPSO end upper chain section and upper wire section Store chain section in vessel chain lockers DOF Subsea 17
Fit recovery clamp to wire Recover wire to deck & secure Cut & remove damaged wire Clean wire end Re-terminate with new wire socket Repair Methodology DOF Subsea 18
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 DOF Subsea 19
Repair Methodology Deploy chain and ACCD tool to seabed DOF Subsea 20
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 DOF Subsea 21
Repair Methodology Deploy chain and ANC ACCD tool to seabed Connect 20m tether lines between HYD and ANC DOF Subsea 22
Repair Methodology Connect hydraulic downline Connect crane to chain end Stroke tool (varied 5-30m) & recover chain DOF Subsea 23
Repair Methodology Once sufficient slack is pulled through, lower chain end link into H-link Insert H-link pin Attach locknut. DOF Subsea 24
Repair Methodology Release load from ANC tool, remove tethers Slide ACCD tool off carriages Recover ACCD tool to deck, recover carriages to deck DOF Subsea 25
Repair Methodology Remove pins to release ACCD ANC tool Lift chain off tool Recover ACCD ANC tool to deck DOF Subsea 26
Repair Methodology All tooling is recovered, leaving only H-links and anchor shackles in the chain leg DOF Subsea 27
Challenges - Range of Weather Leg 2 : 7.5d ops + 6.5d WOW, FPSO in place. Leg 3 : 4d ops + 1d WOW Leg 1 : ~4d ops + 1d WOW Leg 4 : 2.5d ops, no weather downtime. DOF Subsea 28
Challenges Visibility at the Seabed DOF Subsea 29
Challenges - first leg repaired with FPSO in place DOF Subsea 30
Performance - Timeline Engineering awarded Tooling review Vessel contract signed Skandi Hercules mobilised in Singapore Constructability Review 2013 Final risk assessment Jul Aug Sep Oct Nov Award 31/07/2013 Engineering Tool fabrication Tool testing Mobilisation in Taranaki, New Zealand Offshore works 1 month Complete 14/11/2013 Learning curve DOF Subsea 31
Performance - Safety 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 DOF Subsea 32
Key Success Factors Proper detailed Engineering assessment Competent and experienced team, onshore and offshore Preparation testing, trial fits, site integration tests Right assets DOF Subsea 33
Conclusion 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 34
Acknowledgements DOF Subsea wish to recognise and thank OMV New Zealand Limited for permitting the use of the material contained within this presentation. DOF Subsea 35
Questions? Thank you DOF Subsea 36