7/18/2019 NDC Presentation _ Stability for Jackups a New Challenge

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Stability for Jackups

 

A Different

Challenge

Oct 9 2013

Presented by Arun Pushkarna

Asset Integrity Manager

National Drilling Company Abu Dhabi

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Before We Start 

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Let’s Journey Back in Time

Early Assyrian Warship, possibly 8th Century BC

Triremes designed for low Centre of Gravity, high freeboard

Stability awareness existed at that time

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Journey in Time … contd

• Earliest oceangoing

vessels appeared in 2000B.C

• 250 BC: Archimedes

propounded the Laws of

Flotation

• 1746 – 49: Bouguer & Euler

established hydrostatic

stability criteria

• 1860: John Rusell formed

Institute of NavalArchitects

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Journey Continues

• 1867: 2350 Seamen & 137passengers died

• 1876: Compulsory Plimsoll mark on

British ships

• 1890: Marking of loadlineaccording to measurement

mandatory

• 1930: Loadline rules formulated

based on freeboard

• 1966: IMO adopted Loadline Rules

based on subdivision and damage

stability

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IMO Code on Intact Stability

Preamble

“…..the safety of a ship in a seaway involves complex

hydrodynamic phenomena which up to now have not

been adequately investigated and understood…..

….. It is recognized that development of stability

criteria, based on hydrodynamic aspects and stability

analysis of a ship in a seaway, poses, at present,

complex problems which require further research”

4013 Years ……..and Counting!!!

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Let’s Agree on the Definition

StabilityThe ability of a ship to regain

its upright equilibrium position,

after the removal of external

 factor which caused the vessel

to heel at an angle.

Ships are stable when upright 

Ships by design need to be afloat 

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Ships Vs Jack Up Rigs

SHIPS

• Appeared in 2000 B.C

• Spend 99% of time afloat;

1% drydocked

• Water supported• Ships have certified,

licensed Officers

• Has taken 4000 years for

developing stability

JACKUPS

• Appeared in year 1954

• Spend 98% time jacked up;

2% time afloat 

• Soil supported• Few regulatory

requirements

• In our Lifetime…???

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IMO Codes on Stability

Guidance for MODUs

contained in

• Code for Intact

Stability

• MODU Code

Conditions covered by

Codes

 –  Operating Conditions

 –  Severe Storm Condition

 –  Transit Condition

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So……

Are we on Solid Ground?

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2002: This Unit Met Stability Criteria

Jacking system slipped and the hull fell heavily on one side causing

the Port side to drop down with catastrophic consequences

Was the Rig “Stable”?

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2009: So Did This

This rig was preloading when the leg penetrated in soil

causing serious leg and hull damage

Was it “Stable”?

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Three Months Ago

• Tragic consequences ofloss of soil stability

• Damage caused

uncontrolled flooding

• Rig sank in a short time• It was a MODU and

Stability compliant unit 

Why did it get lost?

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The Jackup Difference

• Jackup Rigs are designed to be supported on legs

• Most of their lifespan is in elevated mode

• Risks of loss of “stability” is equally high on location

• Staff frequently experienced but not certified

• No prescriptive standards to appreciate risks

• Soil understanding almost nil

• Codes do not address the requirements

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IMO Requirements

All personnel on mobile offshore

units

As soon aspracticable

MOU

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IMO: OIM Requirements

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What Needs to Change

• Understanding of soil strength

imperative to foundationstability

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Generally Overlooked

• Attachments to legs e.g.,ladders, pipes, etc

• Marine Growth on legs

and drag due to same

• Helicopter landing loads

• Mooring loads for Supply

vessels

• Unbalanced leg loads due

to high drilling fluid

changes

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The Challenges Remain

• Guidance is strongly inclined totransit condition.

• Assumptions of storm calculations

never placed on board

• Guidance to soil testing/preloadingonly weakly referenced in

Operating Manual

• Competency requirements now

defined but lacking details

• No development paths exist 

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Stark Reminder: Unsinkable Titanic (1912)

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Let’s Hope It’s…….

….A New Beginning