November 2017, St. Andrews Decomissioning Conference...
Transcript of November 2017, St. Andrews Decomissioning Conference...
IOGP Report Decommissioning Of CGBS
November 2017, St. Andrews Decomissioning Conference
John Gillies
Joint Interest Project Manager
ExxonMobil International Limited
• International Association of Oil & Gas
Producers
• Members produce 40% of global oil and
gas in 80 countries
• Share knowledge and good practices
• Official “Observer” status at OSPAR
• Decommissioning Committee papers on
Subsea Bundles & Concrete Gravity Base
Structures (CGBS)
2
About IOGP
• 27 structures (12 each UK/Norway)
• Northern North Sea, >90m water
• 17 have been used for oil storage
• Typical 300,000 tonnes (>ten times
more than large jackets)
3
CGBS in OSPAR Area
Ownership (equity tonnage)
4
• Most clustered close to UK/Norway
median; International cooperation essential
• Non OSPAR ownership similar include
Canada, Russia, Australia, othersStatoil
Petoro
Total
ExxonMobil
Shell
Centrica
Taqa
CoP
CNR
Fairfield
Gassled ENI
Apache
Chrysaor
Mitsubshi
Hess
others
Construction Scale & Context
5
• 10 million tonnes installed 1970-1990
• ~20 times weight of all OSPAR derogation
jackets
• 0.5 million truck loads if recovered to shore
• Total aggregate ~1yr. production from UK’s
largest quarry
0
2
4
6
8
10
12
Installed weight by period
Regulatory Framework
• OSPAR 98/3 framework
• 4 derogation requests approved to date
(one oil storage), four pending
Full Removal
• Weight and geometry far exceeds available
lifting vessel, draft exceeds deepest ports
• Re-float feasibility not demonstrated:
1. Re establishing integrity
2. Seabed resistance & withdrawal suction
3. Stability during de-ballasting
• 1m thick, 20m diameter, 100 wire tendons 250 tonnes tension each
• Lifting: legs 8k-tonnes each; dual crane (Thialf, S7000)
Partial Removal
Leave In Place ?
• Leg Collapse ~ 250 years?
• Caisson substantially intact 600-1000 years?
• Collision risk <1:10,000 year event
• Toppling legs feasible with 500 tonne bollard pull
• Quantity and fate of contents
Progress Since 2013 Update
Significant knowledge added:
• Survey, sampling and attic oil removal
developed and proven
• Fate models developed
• Feasibility of leg cutting tested
• Leg lifting concepts developed