WH Fatigue reducing Well construction

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
WH Fatigue problems sources are:
1. Equipment design
2. Equipment application
1.
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Inherent equipment design challenges:
Ultimate well pressure barrier also the main
load carrier for external mechanical loads:
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BOP loads
Riser induced lateral loads (rig movements)
VIV (Vortex induced vibrations)
Accidental loads
Increasing WH loads:
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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
2.
Equipment installation & utilisation risks:
• Cementation dependent installation process; not a
predictable & reliable load transfer; depends on:
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Slurry quality (consistency & contamination) ?
Slurry placement, loss to softer formations => TOC?
Cement curing temperature
Hole geometry / conditions / cleanliness
Conductor movement during cement setting
Imperfect installation will significantly reduce:
 Bending & Fatigue life capacity of well
 Axial/lateral load capacity
 Contingency preparedness
•
Accidental loads much higher than operational
loads (drift off & drive-off)
However:
By application of new installation methods, the
inherent installation risks CAN now be mitigated.
Alternative top hole well construction:
1. Install CAN (ConductorAnchor Node)
Method (by vessel):
• Self weight penetration
• Suction
2. Install Conductor by:
• Driving (Vessel + hammer)
• Jetting (Rig)
• Drill & cement (Rig)
High and testable load capacity:
Example:
@ ∆P=2 bar; (CAN D= 6m)
~600 ton axial
Main functions of CAN :
1. Provide mechanical load support to WH / Conductor
(Capacity ‘’booster’’)
2. Remove cement dependency
(Warrants meeting design requirements)
FE Model: CAN system analyses results:
Hotspot # 1:
WHH/
Cond. weld
Hotspot # 4:
WH/20’’ weld
Hotspot #2:
Cond/1st
Conn. weld
Hotspot #3:
30’’Conn.
Hotspot #5:
20’’Conn.
Cases studied:
1. Stand alone conductor:
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Full soil support and
12m free standing
2. CAN supported conductor
2012-01-30
Slide 5
Hotspot analyses; Main Conclusions:
Conductor Soil support to seabed
Hot spot # 1: Housing/Conductor weld
Reduced soil support
Slide 6
Hot spot # 2: Cond./1st Connector weld
1E+11 * lifetime
Reduced soil support
Hot spot # 3: 1st Connector
1E+13 * lifetime
Reduced soil support
2012-01-30
PPT1169-05_revA.ppt
Slide 7
~1000 * lifetime
Hot spot # 4 : WHH / 20’’ weld
~50 * lifetime
Hot spot # 5 : 1st 20’’ connector
~10 000 * lifetime
Reduced soil support
~500 * lifetime
2012-01-30
PPT1169-05_revA.ppt
Slide 8
FEM Fatigue life results:
Notes:
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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.
Trends: Use high capacity Well Head with
heavy duty, large dimension conductor:
«-- the larger diameter does
not necessarily translate into
better fatigue performance»
(2H Offshore Engineering)
Lessons learnt (1):
1. Conductor Hanger design importance:
Slots for ‘’peeling’’ at extreme bending loads
36’’ Friction type Conductor Hanger
(Design / analyses: Dr. Techn. Olav Olsen)
Lessons learnt (2): Effects of elevator rings!
30’’ Conductor Hanger mounted between elevator rings:
Conclusion:
Never use elevator
rings on upper
conductor joint!
CAN Conductor & developments:
BOP Support System:
Technology
Sea bed BOP Supporter will remove BOP /
Riser induced WH-bending moments (JIP next year):
BOP
1. BOP set down on Well Head
and 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
Conductor
For safer support of:
2. BOP Supporter Pistons
actuated:
- Transfers pre-set part of
BOP weight directly to CAN
- Adapts to BOP frame
- ROV operated
CAN
Reinforcement
for BOP
Stabiliser
Bending moment
=> Fatigue life
problem area
• BOP, plus
• X-mas tree, and
• Capping unit
CAN technology experience:
CAN installations:
Gemini CAN: 1 100 m WD
Cygnus CAN: 860 m WD
Jette CAN: 125 m WD
CAN size: D= 6 m; H= 12 m
Flat top design
Conductor installation options:
Peon:
370 m WD
Dovregubben:
270 m WD
CAN size:
D= 6 m; H= 12 m
Cooper:
250 m WD
Cooper size: D= 6m; H= 8m
1.
2.
3.
4.
5.
6.
7.
Gemini:
Cygnus:
Peon:
Dovregubben:
Jette:
Jette:
Cooper:
Jetted
Jetted
Toe Drive
Drill & cement
Drill & cement
Drill & cement
Drill & cement
Equipment availability (as for WH):
• Available off the shelf for:
• Exploration wells: Reuse rental item
• Production wells: Sales item
Clean and
reuse at next
location
Well architecture; CAN facilitates optimised well design:
Example CAN enabled new well architecture:
CAN
Conventional
200m
Sea bed
30’’
300m
Drilling time:
1. Drill 36’’ hole + conductor set:
3 days
2. Drill 9 5/8’’Pilot Hole:
2 days
3. Drill 17 ½ ‘’ hole + 13 3/8’’ set:
5 days
Total:
10 days
Cuttings disposal volumes:
 36’’; 0.7m3/m =>
70m3
 17 ½ ‘’; 0,16m3/m =>
80m3 = 150m3
20’’
30’’
Drilling time:
 Drill 26’’ hole + 20’’ set:
2 days
 Drill 9 5/8’’Pilot Hole:
0 days
 Drill 17 ½ ‘’ hole + 13 3/8’’ set: 5 days
Total:
7 days
Cuttings disposal volume:
 26’’; 0.35m3/m =>
35m3
 17 ½ ‘’: return to rig => 0m3 = 35m3
20’’x13 3/8’’
String
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
Cement volumes (w/sea bed return):
 Conductor (200% excess) =
70m3
 Surface casing: (20’’x13 3/8’’) = 50m3 = 120m3
800m
Cement volumes (w/sea bed return):
 Conductor:
0m3
 Surface casing (20’’):
15m3 = 15m3
13 3/8’’
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Pre-installed, tested conductor
Rig time & cost savings
Environmental footprint reduction
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!