Classification: Internal

Flexible risers at Kristin

Flexible Pipelines and Risers PSA Norway 12.12. 2007

Nils Terje Nordsve, StatoilHydro

2

Kårstø

DraugenNjord

Ormen Lange

NyhamnaKristiansund

Trondheim

Stjørdal

Brønnøysund

Sandnessjøen

Harstad

Åsgard

Tjeldbergodden

Mikkel

SLP/UK

Heidrun

Kristin

* *

Alve

NorneUrd

Skarv

Idun

HammerfestDrift Nord

3

• 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

Key data for Kristin

Photo: Trond Sigvaldsen

4

Kristin field layout

Grid North

P

R

P-211 Oil

export

N-101

P-101

S-101S-102

Kristin Semi

S-103/S-201

N

P-102/P-201

N-102/N-201

R-102

R-101

R-103/R-201

Fibre optical cable

S

To Åsgard FOC-1/B-401

Åsg

ard

Tran

spor

t P-

121

P-212 NP-212 S

P-212 Gas export loop

FORE

FORE

Åsgard C

S1

S2

S3 S4

FORE

AFT

STB

PORT

16”

Templateand wellslot ID’s:

Pigdirection

Not accessible

Permanent P&A

”S-4 target”

Tofte

Possiblesidetrack to existing N-3H well

10" ID prod (13% Cr.) w/ DEH12" oil export (CS)18" gas export (CS) Umbilical w/ 2" ID centre line3.5“ ID service line (CS)Fibre optical cable (FOC)Direct el. heating (DEH) risersFuture tie-in hubSSIVROV operated ball valveCheck valveDiverless hot tap teeTemporary pig launcher

Completed well

Completion ongoing

Drilled and cappedwell

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 thatall 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)

6

End fitting

Normal gas permeation

Water spray

Leakage detected early November 2006

by annulus vent monitoring system

Rapid pressure build up

Valve opens automatically to release gas when pressure gauge measures 0.5 barg

Gas

dif

fusi

on

or

leakag

e t

hro

ug

h p

oly

mer

lin

er

Air

pressure

1.7 barg

7

Kristin riser S-101 – early work done to identify damage

• Supposed reason was leakage of hydrocarbons from riser bore through the pressure sheath into annulus

• Riser S-101 was depressurized down to ambient pressure

– Frequent pressure relief of annulus continued after ambient pressure was achieved

• 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

7.5

m

20.5

m20

.5 m

RG

T w

ater

leve

l

17 m

1.0

m

Cast insert

Water spraying

(prod. risers only)

RGTs pressurised to ~

1.7 barg (P &GE risers)

8

S-101 – Test to determine location of damageTesting was carried out 20th to 21st November 2006

7.5

m

20.5

m20

.5 m

RG

T w

ater

leve

l

17 m

1.0

m

Cast insert

Damage

location

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 risersconfirmed:S-101, R-101, R-102 andP-211A

– Damage to riser S-102detected 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

Con

tact

pre

ssur

e

Wear depth

Riser RGT•Testing carried out for 0.13 to 2.0 MPa contact pressure

•Wear rate varies linearly with contact pressure

•TP-Flex wears faster than Rilsan (dry and wet)

•Both materials wear faster wet than dry

•Largest difference between Wet TP-Flex and dry Rilsan

14

Roughness typically measured with profile print-outs at three points for all bellmouths

15

Kristin vs. Åsgard B guide tube solution

Kristin, vertical + 5° bend Åsgard, straight 5° inclined

Hang-off at

Riser balcony

Contact force difference:

∆ load=sin 5°x50 tonnes=4.5 tonnes

KRIÅSG B

16

Wear protection collars at Værnes

17

Installation of wear protection collars

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

1

2

3

28/42

29/43

30/44

A

B

ROV handles

Locking mechanism

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

–First riser repaired 20th August 2007

• Complex project with short execution time

• Close co-operation between the

parties involved was required

Cheap

Safe

Fast

25

Damage to riser P-211A before cut-out for welding

26

Damage to the R risers before cut-out for weldingR-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 By welding

R-102

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?