Flexible risers at Kristin, StatoilHydro

Classification: Internal
Flexible risers at Kristin
Flexible Pipelines and Risers PSA Norway 12.12. 2007
Nils Terje Nordsve, StatoilHydro
2
Drift Nord
Hammerfest
Harstad
Alve
Urd
Idun Norne
Skarv
Heidrun
Sandnessjøen
Åsgard
Kris
tin
*
*
Brønnøysund
Mikk
el
Njord
Draugen
Stjørdal
Tjeldbergodden
Trondheim
Ormen Lange
Kristiansund
Nyhamna
Kårstø
SLP/UK
3
Key data for Kristin
• Water depth: 320 m
• Reservoir pressure: 911 barg
• Reservoir temperature: 170 °C
• Production capacity
– Gas: 18.3 MSm3/sd
– Condensate: 20000 Sm3/sd
• Number of risers: 9
• Number of umbilicals: 5
Photo: Trond Sigvaldsen
4
Kristin field layout
Possible
sidetrack to
existing N-3H
well
N
Åsgard C
N-102/N-201
N101
P
”S-4 target”
FORE
Template
and well
slot ID’s: AF
S3T S4
ST
S2 S
B
1
FOR
E
Grid
North
P-102/P201
POR
T
P101
Kristi
n
Semi
To Åsgard
FOC-1/B-401
l
le
Oi
cab
11 t
2
cal
i
P or
t
p
p
ex re o
Fib
P-212
N
P-212
S
P-212 Gas export
loop
Åsgard Transp
ort
P-121
Permanent
P&A
Not
accessible
Pig
direc
tion
S-103/S201
S
R-103/R-201
Toft
e
S101
S102
R
FORE
R101
R-102
10" ID prod (13% Cr.) w/ DEH
12" oil export (CS)
18" gas export (CS)
Umbilical w/ 2" ID centre line
3.5“ ID service line (CS)
Fibre optical cable (FOC)
Direct el. heating (DEH) risers
Future tie-in hub
SSIV
ROV operated ball valve
Check valve
Diverless hot tap tee
Temporary pig launcher
16
”
Completed well
Completion ongoing
Drilled and capped
well
Drilling commenced
Planned well
Spare well slot
Not available well slot
5
Kristin risers – historical account until early November 2006
• The export risers were parked on seabed in October 2004
• The flexible risers were tied back to the platform in April to June 2005
• Annulus vacuum testing performed in May/June 2005 confirmed that
all risers were intact after installation
• First production took place 3rd November 2005 (through S-101)
• Problem with one riser detected early November 2006 (S-101)
Leakage detected early November 2006
End
fitting
by annulus vent monitoring system
Gas diffusion or leakage through polymer liner
Valve opens
automatically to
release gas when
pressure gauge
measures 0.5 barg
Water
spray
Air
pressure
1.7 barg
Normal
gas
permeation
Rapid
pressure build
up
6
7
Kristin riser S-101 – early work done to identify damage
•
The pressure in the riser was increased to 80 bar;
the riser remaining out of service
•
The pressure in the Riser Guide Tube was reduced
to ambient pressure
– Frequent pressure relief of annulus ended
=> The phenomenon was due to leakage in
the outer sheath
20.5 m
1.7 barg (P &GE risers)
Cast insert
20.5 m
– Frequent pressure relief of annulus continued
after ambient pressure was achieved
RGTs pressurised to ~
17 m
Riser S-101 was depressurized down to ambient
pressure
(prod. risers only)
RGT water level
•
Water spraying
1.0 m
Supposed reason was leakage of hydrocarbons
from riser bore through the pressure sheath into
annulus
7.5 m
•
8
S-101 – Test to determine location of damage
20.5 m
Cast insert
RGT water level
location
7.5 m
Damage
1.0 m
17 m
20.5 m
Testing was
carried out 20th
to 21st
November 2006
9
Kristin risers – damages detected
• Scheduled vacuum tests in November 2006 showed that all export risers were
intact
• Vacuum tests in December 2006
– Damage to four risers
confirmed:
S-101, R-101, R-102 and
P-211A
– Damage to riser S-102
detected May 2007
10
Consequences of damage
• Tensile armours are exposed
– Possible wear against RGT inner
surface
– Corrosion fatigue in aerated sea
water
• Riser calculated fatigue lives in aerated
sea water
– Production risers: Five to eight years
– Condensate export riser: 2.5 years
– Gas export risers: Six months
11
Potential causes – as evaluated at an early stage
• Possible material problem?
– TP-Flex™ is a new material
– Brittle behaviour?
– Bad wear resistance?
• Mechanical damage – due to inadequate Riser Guide Tubes?
– Surface roughness?
– Misalignment?
12
Material testing performed
• Fatigue of tensile armours
• Tensile testing of outer sheath
• Wear testing of outer sheath
Fracture
13
Preliminary wear test results of outer sheath materials
•Testing carried out for 0.13 to 2.0 MPa contact pressure
Riser
RGT
•Wear rate varies linearly with contact pressure
•TP-Flex wears faster than Rilsan (dry and wet)
•Both materials wear faster wet than dry
Contact pressure
•Largest difference between Wet TP-Flex and dry Rilsan
Wear depth
14
Roughness typically measured with profile
print-outs at three points for all bellmouths
15
Kristin vs. Åsgard B guide tube solution
Hang-off at
Riser balcony
ÅSG B
Contact force difference:
∆ load=sin 5°x50 tonnes=4.5 tonnes
Kristin, vertical + 5° bend
Åsgard, straight 5° inclined
KRI
16
Wear protection collars at Værnes
17
Installation of wear protection collars
A
1
2
3
28/42
29/43
30/44
B
1. Mount clamp anti-sliding clamp (A) on riser
2. Install collars consecutively; neck down
3. Mount extra locking clamp (B) on neck of lowermost collar
4. Hang clump weight on lowermost collar
5. Release and remove anti-sliding clamp (A)
6. Release collars from clump weight
7. Collars will then slide into the RGT driven by buoyancy
Locking mechanism
ROV handles
18
Wear protection collars on R-101 entering RGT
19
Experiences from installation of wear protection
• Practice makes perfect:
– From more than one hour per collar to typically four collars per hour
• Due to friction against the RGT the collars may stop on their way
upwards:
– Will eventually move during rougher seas
– Tilting the platform and/or adding buoyancy would help
• One some collars the locking mechanism opened
20
Examples of wear protection collars that have opened
P-211A
P-212S
21
16 collars missing on riser P-212N
22
Lost collar - Picture taken after recovery
23
Wear protection collar – locking mechanism
24
Dry riser repair
• Project with Aker Reinertsen
– Kick-off 28th March 2007
Cheap
– First riser repaired 20th August 2007
• Complex project with short execution time
• Close co-operation between the
parties involved was required
Safe
Fast
25
Damage to riser P-211A before cut-out for welding
26
Damage to the R risers before cut-out for welding
R-101
R-102
27
Damage to the S risers before cut-out for welding
S-101
S-102
28
Connection of patch to outer sheath
By Sikaflex
R-102
By welding
29
Application of heat shrink R-102
30
Temporary offloading of condensate during repair of P-211A
31
Summary of damages and repairs
• Damages were detected as follows:
– S-101: 5th November 2006
– R-101: 19th November 2006
– R-102: 25th November 2006
– P-211A: 16th December 2006 (vacuum test – OK in November)
– S-102: 11th May 2007
• Repair carried out:
– R-102 repaired 20th August 2007; second time 5th October 2007
– S-101 repaired 28th August 2007
– P-211A repaired 10th September 2007
– R-101 repaired 18th September 2007
– S-102 repaired 25th September 2007
32
New risers
• Contract with Technip:
– Delivery 01.09.2008
– 6 new risers (1 x condensate export, 1 x gas export, 4 x production)
• Outer sheath material:
– Rilsan for all risers
– Rilsan protective sheath in RGT area
– Cooling of production risers required for flow temperatures
exceeding 92°C
• Wear protection collars most likely to be used for new risers
33
Lessons learned so far
• Damage is due to wear rather than fracture
• Rilsan has better wear resistance than TP-Flex
• Wear resistance is better dry than wet
• Riser Guide Tubes are important
– Geometry
– Inner surface condition
• Riser configuration is important
• Locking mechanism of Wear Protection Collars is crucial
34
Concluding remarks
• Wear protection collars installed on all risers
• Problems with the locking mechanisms encountered
– Design changed
• Fast track repair project
– All suppliers have met schedule
– No HES incidents
• Work ongoing to clarify cause of damages
– Wear of outer sheath against inner surface of RGTs
– RGT geometry?
– Riser configurations?