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8/4/2019 Presentation Offshore
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Presented by: Erfan Ahmad
MSc Structural Engineering
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Overviewwhat is an offshore oil structure?
Offshore platforms are used for exploration and processing of oil and gas from underseabed.
The first offshore platform was built in 1947 off the coast of Louisiana in 6m depth. Since then 12,000 platforms in various depths have been constructed around the
world.
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Types of offshore oil structure Fixed structureBuilt on concrete or steel Legs or both. Examples:
Gravity platforms: Made of reinforced concrete, very large and massive Weight.
It is impractical for water depths beyond (300)m.
Jacket platform: It is frame structure made of tubular steel.
Depth normally (400 to 500)m
Compliant Tower: Consist of slender flexible Towers steel and a pile Foundation supporting.
Depth normally (460 to 910)m
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Types of offshore oil structure Floating PlatformsIt is cable tensioned, use for deeper water
Examples:
Tension Leg platforms (TLPs) It is floating facilities ,tied down to the seabed by vertical
Steel tubes.
Depth normally (1500)m
Semi Submersible (FPS) It is stays in place by long Catenary-Shaped mooring lines.
Depth normally (2000)m
Spa Platforms
First built off the USA coast in 1997. Concept of a large diameter single vertical cylinder
supporting deck.
Depth normally (2300 to 3000)m
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Accidents in offshore oil platforms Collision with vessels (Mumbai (Bombay)High
North Platform). Location: Mumbai High, IndianOcean
Fire or blowout (GSF Adriatic IV Jack-Up) Location:Temsah, Mediterranean Sea, Egypt
Extreme Weather (West Gamma Jack-up) :Location:German Bight, North Sea
Overturning (Parker 14-J Jack-up Barge)
Location: Chandeleur Area, Gulf of Mexico
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Accidents in offshore oil platforms
Fatigue (Alexander L. Kielland Semi-Sub) Location:
Ekofisk Field, Norwegian Continental Shelf
Other incident(crane load lines broke):(Petronius A Platform) Location: Viosca Knoll, Gulfof Mexico
Design and construction errors (Maersk VictoryJack-Up) Location: Gulf Saint Vincent, SouthAustralia
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Statistics of accidents in offshore oil platforms
Comparison of the number of incidents in differentgeographical sectors of the UKCS.
17 incidents in1998
14 incidents in 1999
29 incidents in 2000
20 incidents in 2001
10 incidents in 2002
35 incidents in 2003
20 incidents in 2004 to august 31st
Number of accidents and accident frequencies
(per unit-year). N is No; of occurrences, F isaverage annual frequency)
Fixedplatform
Floatingplatform
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Robustness and collapse What is robustness?
It is the ability of a structure to sustain damage which is not disproportional to thetriggering event.
It is quantified through progressive collapse analysis
It is not easy to measure because it depends on many factors Magnitude of the accidental load
Position and direction of load
Duration of load
Structural form
Specific resistance of elements
Post-collapse behaviour of elements (brittle or ductile)
Energy absorption
Materialdependent
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Robustness in offshore structures What are the current methods used in design? Strength design
e.g. installation resists collision without deformation- ship deformsand dissipates major part of energy
Ductility design
e.g. installation deforms and dissipates major part of energy- shipremains virtually undamaged
Shared energy design
Both ship and installation deform and contribute substantially to
energy dissipation
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Objective of dissertation To analyse robustness of 3D offshore oil steel structure when member of the
structure is damaged by external load.
Vessel
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methodologyBackground of offshore oil platforms
Define accidental scenario
Robustness and progressive collapseAnalysis of a fixed platform structure
model analysis
Discussion and Conclusion
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Expected outcomesObtain force displacement
Buckling in tubular members
Strength of connections
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Time scheduleliterature Review
case studies
Model analysis
discussion of result
conclusion
literature Reviewcase studiesModel analysisdiscussion of resultconclusion
start date 25/07/201114/08/201127/08/201125/09/201108/10/2011
number of date to complete 211430147
stop date 14/08/201127/08/201125/09/201108/10/201114/10/2011
Time Schedule
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