DRAUGEN SURFACE CASING CORROSION · 2018-01-17 · Initial Reservoir Pressure 165 bara, hydrostatic Reservoir Fluid light under-saturated oil, ... 177 Barg Formation Strength GLV

Copyright of Norske Shell A/S

DRAUGEN SURFACE CASING CORROSION

Well Integrity Seminar 2014

Oddvar Husby

Well, Reservoir and Facilities Management Lead

1June 2014

Use this area for cover image(height 6.5cm, width 8cm)


DRAUGEN

2

� 6 platform producers, 5 operational

� 8 subsea wells, 7 operational

� Water injection, 2 templates

Draugen 6407/9, PL093

Water depth 251 m

Reservoir Type shallow marine, upper shore face sandstone reservoir

Structure low relief N-S trending anticlinal structure

Areal extend 20 x 6 km

Max Vertical closure 50 m

FWL 1640 TVDSS

Reservoir Upper Jurassic Rogn/Garn

Porosity 28-32 %

Permeability 5+ Darcy

Initial Reservoir Pressure 165 bara, hydrostatic

Reservoir Fluid light under-saturated oil, with no associated gas cap

A/S Norske Shell (44.56%)

Chevron Norge AS (7.56%)

Petoro AS (47.88%)June 2014


COMPLETION A-1, A-2, A-3, A-6

Standard completion:

� 7” x 5.5” tubing

� 10 ¾ x 9 ⅝” production casing

� 13 ⅜” intermediate casing

� 18 ⅝” surface casing – load bearing

� 26” conductor

� Open hole with 6 ⅝” slimpack screens,

300 µ

� 1 GLV: PTC high reliability valve

� Below SSSV;

� Part of primary barrier

3June 2014

PSV

KWV PWV

PUMV

PLMV

A

A GLIS

SOV

B SOVs

B SOV

C

SSSV

177 Barg

Formation

Strength

GLV

246,4 Barg

Formation

Strength

Packer

Slimpack

Screen

(281m)

Well 6407/9 A1

Platform Well - Gaslifted (via A ann)


DRAUGEN CONDUCTOR/SURFACE CASING SCHEMATIC

� All wells located within the GBS

(Gravity based structure)

� Water level in GBS follows sea level

� Fluids in D-annulus holds a

temperature of 40 – 50 ⁰C

4June 2014


A5 WELL DROP EVENT 2002

December 2002:

� Shut in the well for coiled tubing rig up

� Thermal contraction did not take place -the well hung up near surface

� Sudden release of well

� Initial 26 cm drop, total of 44 cm over 7 days

Root causes:

� Port left open on conductor

� Splash zone corrosion of surface casing

� Centraliser mounted in proximity of top conductor

� Hang up of centraliser

� Shock load on the well

5June 2014

Xmas Tree Platform

Water level in shaft

~50 m

2. Hang up at top conductor, 10 cm above cold position

4. Failure of 18 5/8” casing

3. Release at hang up point

1. Shut in well, thermal contraction


A5 RECOMMENDATIONS AND ACTIONS

1. Prevent further corrosion on A-5

� Experience transfer from Brent-field

� Separate water-air interface with vegetable oil

2. Seal the port in the conductor

3. Inspect the other Draugen wells

� Wells A-1, A-2, A-3, A-4 and A-6 inspected, no wear found

� Conductor ports confirmed closed

4. Recommend to keep conductors water filled

5. Consider implementing corrosion protection on surface casing

6. Consider periodic wall thickness monitoring

7. Study contributing factors to wellhead growth

6June 2014


PEC INSPECTION PROGRAM

The Pulsed Eddy Current (PEC) tool

(developed by Shell) measures average

wall thickness (over a footprint of 4cm)

without need for direct contact with the steel

7June 2014

2003: Inspection of platform wells showed

casings and conductors in good order,

except for A-5 that showed significant wall

loss (up to 60% at failure point)

2008: D-PEC surveys carried out, lower

sections (around sea level depth) completed

and OK. Upper sections not surveyed due

to access problems or time restrictions


A-4 PEC RESULTS 2013

8June 2014


A-6 PEC RESULTS 2013

9June 2014


PHOTOS AND BOROSCOPE VIDEO SNAPSHOTS

10

Conductors photos from the weather deck

Surface casing corrosion; Photos from Upper Mezzanie deck; Corrosion products preventing access

June 2014


A4 LEAK

11

� A4 leak in the 18-5/8” casing,

0.5 - 1 m from top of the

conductor

� Discovered during D-annulus

top up;

� Detected by boroscope;

June 2014


RESULTS – PEC MEASUREMENTS 2013

PEC and Boroscope Measurements carried out on conductor and outer 18-5/8”

(surface) casing in November/Desember 2013

� A small leak discovered in 18-5/8” casing on A-4

� PEC og borsoscope access difficult because of corrosion products present in the annuli,

no measurements in large parts of the casings

� Samples taken of water in the annuli for analysis, indicate significant amounts of salts –

presence of untreated sea water that could cause microbiological corrosion

� Solid samples have been collected and analysed – mainly corrosion products with

minor additives (<5%), such as calcite (CaCO3), Halite (KCl), Sylvite (KCl)

12June 2014

DepthWall thickness loss

A1 A2 A3 A4 A5 A6

0-10 m 23 % 8 % 24 % 11 % N/A 43 %

10-35 m 10 % N/A N/A 7 % N/A N/A

35-65 m 4 % 6 % 7 % 6 % 21 % 5 %


RESULTS – AXIAL LOAD SAFETY FACTORS

Surface casing Conductor

Axial SF Wall loss Axial SF1 Wall loss

A-1 1.82 23 % 6.31 11 %

A-2 2.61 9 % 6.26 11 %

A-3 1.77 24 % 6.21 11 %

A-4 2.27 12 % 6.75 15 %

A-5 N/A2 21 % > 6 10 %

A-6 1.28 43 % 6.04 12 %

13June 2014

� Results are for corroded pipe body; connection performance has not been analysed.

� Results assume well shut-in sufficiently long to reach undisturbed geothermal temperature gradient.

� Axial SF at interventions, e.g. scale squeeze, will be significantly lower

1Assuming that the conductor takes all of the surface casing load

2The permanent platform suspension structure protects the surface casing from axial load


RESULTS – CORROSION MECHANISM

Direct causes

� Oxygen induced corrosion

� Splash zone introduced by regular

water-top ups: Relatively stable water

level with good access to oxygen

� The difference in corrosion between

wells is not fully understood

Indirect causes

� Insufficient understanding of risk

� Unclear responsibilities

� Well design

14June 2014

Estimated D-annulus water level


OVERVIEW OF ACTIVITIES UNDERTAKEN

1. Short-term mitigating actions

� Procedures for well operations

� Secure wells A-4 and A-6 with clamps

2. Capture learning

� Incident investigation

� Update operational procedures and practices

3. Understand and mitigate corrosion mechanism

� Rape seed barrier in all wells

� Monitoring, inspection and maintenance program to ensure effectiveness of the corrosion inhibition

4. Further map the corrosion extent

� Data acquisition, review additional or alternative measurements

� Clean-out of D-annulus to ease access for new inspections will be evaluated

5. Long term solution for securing the wells

� Team nominated to develop a plan for long term solutions for all wells at risk

� The plan must be aligned with the abandonment plan for the field

15June 2014


DRAUGEN A6 CLAMP INSTALLATION – DECEMBER 2013

16June 2014


PRELIMINARY REPAIR OPTIONS FOR A-6

� Proposal 1 – Grout filled section of conductor

� Proposal 2 – Grouted enclosure over section of surface casing

� Proposal 3 – Composite wrapped surface casing with support on conductor

� Proposal 4 – Composite wrapped surface casing with support on main deck

June 2014 17


SUMMARY

� A-5 well drop event led to focus on surface casing corrosion

� PEC and boroscope inspection programme from 2003

� Severe corrosion of A-6 surface casing discovered in 2013

� Corrosion inhibition through barrier fluid on top of water filled D-annulus

� Repair of A-6 surface casing under planning

June 2014 18


Q & A

June 2014 19


CONCEPT 1 - GROUT FILLED SECTION OF CONDUCTOR

Advantages:

� Economic

� Standard Furmanite components

Disadvantages:

� Grout adhesion

� Weight and size

June 2014 21


CONCEPT 2 - GROUTED ENCLOSURE OVER SECTION OF SURFACE CASING

Advantages:

� Axial Support

� Standard Furmanite components

Disadvantages:

� Length of enclosure

� Weight and size

June 2014 22


CONCEPT 3 – COMPOSITE REPAIRED SURFACE CASING WITH SUPPORT ON CONDUCTOR

Advantages:

� Restores structural integrity

� Flexibility in composite length

Disadvantages:

� Large gripper assembly

� Grippers reliance on friction

23June 2014


CONCEPT 4 – COMPOSITE REPAIRED SURFACE CASING WITH SUPPORT ON MAIN DECK

Advantages:

� Restores structural integrity

� Flexibility in composite length

Disadvantages:

� Large gripper assembly

� Grippers reliance on friction

24June 2014

DRAUGEN SURFACE CASING CORROSION · 2018-01-17 · Initial Reservoir Pressure 165 bara, hydrostatic Reservoir Fluid light under-saturated oil, ... 177 Barg Formation Strength GLV

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