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

Preview

Background on DP Drillship Operations

DP Watch Circles Emergency Disconnect

Drift-off Analysis Techniques

Operations

Conclusions

2

Drillship Operations

Drilling Riser

Blow Out Preventer Casing

DP Thrusters

Derrick

Heave Compensator Rig Floor

Riser Tensioners

3

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

4

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.

5

, ..... Drift off analysis results

\. ,J

n EDS 90 sec , ..... Time r " r " Yellow

POD > Red Alert

> Alert I Offset I Offset "- .,J "- ~ \. ~ I ~1 ~1

Tpod = t (sec) T RED= t- EDS Time (sec) T YELLOW = t- EDS Time (sec) - 90 sec

Watch Circles: Concept

6

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

7

320 310 300

Watch Circles: Compass View

8

600

500

400 'ui ... :::::l (.) X w

Drift Off Analysis - Vessel Excursion From Well Centre - Vessel Excursion - 10 ppg Mud Weight & 1455 k/p Top Tension

POINT OF DISCONNECT

469 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

a> 300 RED ALERT OFFSET ~ 281 - - - - - - - - - - - - - - - - - - - - - - - - -~ 2 C

2 200 ;:: 0 I

100

70sec I 1 I

187 0 L--~==--+-----+---+----+--+----+--

0 20 40 60 80 100 120 140 160 180 200 220 240

Time (sec)

257

260 280 300

Drift-Off Analysis Results

9

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: OSullivan, 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

10

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

11

_,. I\.) w ~ 0 0 0 0

0 0 0 0 0

I I I I I

1430 3/27

1230 3/28

1200 3/29

2200 3/30

2200 3/30

2100 4/1

2100 4/2

2200 4/3

2130 4/4

0300 4/6

0300 4/7

0900 4/8

1500 4/9

1500 4/10

0900 4/12

0900 4/13

I ~ I I ::0 "&'

,, ,, CD C C Q. 0 '< '< r :;E () () 3 r 0 0 r-t- 3 C C ,, "O "O >< r-t- CD CD CD

,, Q. Q. Q. >< ::0 "&' CD CD

Q. Q. 0 r :;E 3 r r-t 3

;::;:

Fixed vs. Dynam

ic (Fully Coupled)

Courtesy of W

ood Group K

enny 12

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.

13

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Slide Number 1Preview Drillship OperationsDrilling Riser ManagementEmergency DisconnectWatch Circles: ConceptWatch CirclesWatch Circles: Compass ViewDrift-Off Analysis ResultsDrift-Off Analysis TechniquesOperationsFixed vs. Dynamic (Fully Coupled) ConclusionsSlide Number 14