Emergency Disconnect Procedures: Industry Approaches to DP Drift-Off - - PowerPoint PPT Presentation

Emergency Disconnect Procedures: Industry Approaches to DP Drift-Off Analysis

James N. Brekke, P.E.

Account Manager, Offshore Energy Project Development American Bureau of Shipping BSEE Standards Workshop – May 8, 2015

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 Background on DP Drillship Operations  DP Watch Circles – Emergency Disconnect  Drift-off Analysis Techniques  Operations  Conclusions

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Drillship Operations

Drilling Riser Blow Out Preventer Casing DP Thrusters Derrick Heave Compensator Rig Floor Riser Tensioners

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zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Drilling Riser Management

 Objective:

 Protect the vessel, riser and well  Establish limits on operations

 Scope:

 Riser deployment  Riser tensioning  Emergency disconnect  Riser recoil  Storm hang-off

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zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Emergency Disconnect

 What is emergency disconnect?  How often does it happen?  Allowable limits:

 Conductor pipe – bending stress  Wellhead – bending moment  Riser bottom flex joint – limiting angle  Riser top flex joint – limiting angle, moonpool contact  Riser slip joint – stroke limits  Riser tensioners – stroke limits

 How are these managed? Watch Circles and Drift-Off Analysis.

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Drift off analysis results

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Watch Circles: Concept

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zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Watch Circles

 Thresholds that are color-coded yellow and red  Established using drift-off analysis  Based on scenarios of drift-off under total loss of power, drive-off,

degraded thrusters, or other events

 Offset definitions:

 Point of disconnect (POD) – offset at which any allowable limit is

first exceeded

 Red – offset at which the emergency disconnect sequence (EDS)

must be activated. Drillpipe would be sheared during EDS.

 Yellow – offset at which preparations begin prior to EDS

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320 310 300

Watch Circles: Compass View

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Drift Off Analysis - Vessel Excursion From Well Centre

• Vessel Excursion - 10 ppg Mud Weight & 1455 k/p Top Tension

POINT OF DISCONNECT

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• a> 300

RED ALERT OFFSET ~

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Drift-Off Analysis Results

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zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Drift-Off Analysis Techniques

 Fully coupled analysis (state-of-the-art)

 Riser analysis fully coupled with vessel analysis  Includes riser restoring force, riser dynamics

– Ref: O’Sullivan, Soles, Dib, “Fully Coupled EDS/Drift-off Analysis for a Harsh Environment Deepwater Site” OMAE 2004 – 51631

 Uncoupled techniques

 Vessel drift-off analysis without riser, static riser analysis  Vessel drift-off analysis without riser, dynamic riser analysis

 Fixed offset

 Constant watch circle sizes, typically based on % water depth

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zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Operations

 Dynamic Watch Circles (updates on the rig every 6 hours)

 Prevailing or forecast weather  Changes in riser top tension or drilling mud weight  Can use coupled or uncoupled drift-off analysis

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Fixed vs. Dynamic (Fully Coupled)

Courtesy of Wood Group Kenny

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zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Conclusions

 Use of fully-coupled drift-off analysis makes a difference;

providing a more realistic solution

 Regular updates of watch circles also make a difference,

accounting for:

 Prevailing weather  “What-if” forecast weather  Changes in top tension and mud weight

 Fully-coupled drift-off analysis is referenced as part of marine

drilling riser assessments in ISO 13624-1 and ISO 13624-2.

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