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Ptil Seminar 06.12.12:

Subsea Wellhead fatigue

Learning and experience sharing,

preventing major accidents

WH Fatigue reducing Well construction:

We CAN do much better with available means!

www.neodrill.no

http://www.fp.fo/Default.aspxhttp://www.fp.fo/Default.aspx

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WH Fatigueproblems sources are:1. Equipment design2. Equipment application

1. Inherent equipment design challenges:

Ultimate well pressure barrier also the main

load carrier for external mechanical loads: BOP loads

Riser induced lateral loads (rig movements)

VIV (Vortex induced vibrations)

Accidental loads

Increasing WH loads: Much higher BOP loads (250 => 400 ton)

New tensioning systems & higher riser tensions

Equipment standards render design improvements

difficult to undertake

Enormous consequences of design changes

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FE Model: CAN system analyses results:

2012-01-30 Slide 5

Hotspot #2:Cond/1st

Conn. weld

Hotspot # 4:WH/20 weld

Hotspot #3:30Conn. Hotspot #5:

20Conn.

Hotspot # 1:WHH/

Cond. weld

Cases studied:

1. Stand alone conductor: Full soil support and

12m free standing

2. CAN supported conductor

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Slide 6

Hotspot analyses; Main Conclusions:

Conductor Soil support to seabed

Reduced soil support

Hot spot # 1: Housing/Conductor weld

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Reduced soil support

Hot spot # 2: Cond./1st Connector weld

Hot spot # 3: 1st Connector

Reduced soil support1E+11 * lifetime

1E+13 * lifetime

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Reduced soil support

Hot spot # 4 : WHH / 20 weld

Hot spot # 5 : 1st 20 connector

~1000 * lifetime

~50 * lifetime

~10 000 * lifetime

~500 * lifetime

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FEM Fatigue life results:

Notes: The CAN support case gives a predictable & safe operating condition for the WH equipment!

The case Without CAN soil to mudline is an ideal case, as it will not be possible to provide

perfect soil support to mudline for conventionally cemented conductors over time.

Experience show:

Initially most wells will be between having Soil to mudline and 12 m soil shortfall

during drilling operations The conductor free-point will be gradually worked downwards due to BOP movements.

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Lessons learnt (1):

36 Friction type Conductor Hanger(Design / analyses: Dr. Techn. Olav Olsen)

1. Conductor Hanger design importance:

Slots for peeling at extreme bending loads

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Lessons learnt (2): Effects of elevator rings!30 Conductor Hanger mounted between elevator rings:

Conclusion:Never use elevator

rings on upper

conductor joint!

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2. BOP Supporter Pistons

actuated:

- Transfers pre-set part of

BOP weight directly to CAN

- Adapts to BOP frame

- ROV operated

1. BOP set down on Well Headand connected to same by

WH Connector: (250-350 ton

set down weight)

Axial BOP load transferred to

CAN through WH Connector

and Conductor hang-off

gimble.

Sea Bed

CAN

Reinforcement

for BOP

Stabiliser

Conductor

BOP

CAN Conductor & BOP Support System:Technology developments: Sea bed BOP Supporter will remove BOP /

Riser induced WH-bending moments (JIP next year):

For safer support of:

BOP, plus X-mas tree, and

Capping unit

Bending moment

=> Fatigue lifeproblem area

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Peon: 370 m WDDovregubben: 270 m WD

CAN size: D= 6 m; H= 12 m

Cooper: 250 m WD

Cooper size: D= 6m; H= 8m

CAN installations:

Gemini CAN: 1 100 m WD

Cygnus CAN: 860 m WD

Jette CAN: 125 m WDCAN size: D= 6 m; H= 12 m

Flat top design

Conductor installation options:1. Gemini: Jetted

2. Cygnus: Jetted

3. Peon: Toe Drive

4. Dovregubben: Drill & cement

5. Jette: Drill & cement

6. Jette: Drill & cement

7. Cooper: Drill & cement

CAN technology experience:

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Equipment availability (as for WH): Available off the shelf for: Exploration wells: Reuse rental item

Production wells: Sales item

Clean andreuse at next

location

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30

30

20

20x13 3/8

String

CAN

300m

13 3/8800m

Drilling time:

Drill 26 hole + 20 set: 2 days

Drill 9 5/8Pilot Hole: 0 days

Drill 17 hole + 13 3/8 set: 5 days

Total: 7 days

Cuttings disposal volume:

26; 0.35m3/m => 35m

3

17 : return to rig => 0m3= 35m

3

Cement volumes(w/sea bed return):

Conductor: 0m3

Surface casing (20): 15m3

= 15m3

Drilling time:

1. Drill 36 hole + conductor set: 3 days

2. Drill 9 5/8Pilot Hole: 2 days

3. Drill 17 hole + 13 3/8 set: 5 days

Total: 10 days

Cuttings disposal volumes:

36; 0.7m3/m => 70m

3

17 ; 0,16m3/m => 80m

3= 150m

3

Cement volumes(w/sea bed return):

Conductor (200% excess) = 70m3

Surface casing: (20x13 3/8) = 50m3 = 120m3

Conventional

Sea bed200m

Example CAN enabled new well architecture:

Pre-installed, tested conductor

Rig time & cost savings Environmental footprint reduction

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Closing remarks:

Cement is an unreliable means of Conductor / WH installation!

Bigger is not always better!(Larger conductor OD higher fatigue life capacity!)

Better well foundation added well costs! (Saves rig time & troubles!)

Method of installation of WH-Systems is the key to satisfying

ALARP requirements (also for production wells)!

The industry has the means to attain much higher fatigue life

time and load capacity from all present Well Head systems!

(Especially if removing bending moments from the WH!)

Yes, we CAN