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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