Ageing Platform Wells - 2H Offshore€¦ · 10 0 5 10 15 20 25 30 35 40 45. PEC reading [%] PEC reading [mm] Distance from top of Conductor [m] Platform XYZ - Well TRS-23 - 20" Casing

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Ageing Platform Wells – Investigation & Remediation

27th April 2017

D Roberts


Agenda

Introduction – number > cost

Platform well build

Corrosion mechanism – accelerators

Investigation

Remediation methods

Summary


253 Installations

Platforms

127 Un-manned Platforms

126 Manned

Platforms

5

34

27

14

20

% Platforms Per Age Range

Older conductors and surface casings may be subjected to corrosion with wall loss of 50% or more

0

20

40

60

80

100

120

140

160

No

. P

latf

orm

s

~ 253 platforms

in the North Sea

Platform Wells – North Sea Status

Source: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/482440/Installations_December_v1.xls

Centralisation of the conductor

within the platform guides often reduces

over time due to slackening of the

centralisers or a total loss.

Average age of an

operational North Sea platform is

28years

60 163 Gas Oil

Oil/Gas 10 Condensate 20 Learn more at www.2hoffshore.com

Structural Failure - Cost Effect


Platform Well Construction

Well built on the surface casing, conductor acts as a marine protector only.

Well built on the conductor – latched or may lift off when hot (Hybrid). The

GAP

HYBRID – no lockdown? More complex!


Corrosion mechanism

HAT

MSL

LAT

Mud circulation ports or subsea

breach

O2

HEAT

HEAT

Microbial &

Anaerobic

Corrosion

O2

Corrosion

AcceleratedO2

Corrosion

Debris caps top corrosion


4 Steps to be Considered

1. Calculate well “as-built” weight – Size of the initial forces

2. Measure remaining wall thickness – Quantity of steel carrying forces

3. Assess well criticality – re-model with reduced performance & added external & operational loads

4. Implement corrective method – Fix if required & re-model


Step 1. Well Load (Weight)

Option 1 Well Build Predictive Modelling

Reasonable well data, a load / displacement calibration point is useful. Learn more at www.2hoffshore.com

Direct Measurement

Option 2 Direct In-Situ measurement ASTM E837

Manufacturing stresses can influence readings!


Health Check

Wellhead

TOC

TOC

TOC

Packer

Do in-situ load and model match?

Has the well maintained its as-built load and GAP?

Are all the springs still working?

If structural spring fails the rest will take its share whether they are capable or not!


STEP 2. Remaining Wall Thickness Pulsed Eddy Current (PEC)

method – field proven

Ability to read thickness of “good steel” through thick corrosion / marine product ~ 20mm

Integrated camera

Multiple historic surveys gives corrosion rate

C-PEC measures simultaneously

0

20

40

60

80

100

120

0

5

10

0 5 10 15 20 25 30 35 40 45

PE

C r

ea

din

g [

%]

PE

C r

ea

din

g [

mm

]

Distance from top of Conductor [m]

Platform XYZ - Well TRS-23 - 20" Casing - 2012 PEC wall thickness measurements

D-PEC Nov2007

LFlu

id

level

2009

H

AT

Vertical

Position Clock Position [hours]

[mm] 2 4 6 8 10 12

0 16.5 12.5 17.2 16.9 15.1 16.5

-100 16.8 12.4 17.0 16.7 13.8 16.4

-200 16.7 10.4 16.4 16.7 11.3 16.1

-300 16.5 10.5 14.3 16.5 12.2 15.9

-400 17.1 9.6 13.3 16.4 11.1 16.4

-500 16.9 9.7 12.9 16.3 12.5 16.6

-600 16.5 10.2 13.9 16.3 15.3 16.7

-700 16.9 9.1 13.4 16.0 16.5 16.4

-800 16.6 8.6 11.9 16.1 16.4 16.7

-900 16.9 8.4 11.9 16.3 16.5 16.8

-1000 16.5 7.9 12.0 16.4 16.4 16.7

-1100 16.1 8.0 13.5 16.2 14.2 16.6

-1200 14.9 8.1 13.0 16.2 16.5 16.3

-1300 13.9 8.5 13.8 16.3 16.7 16.1

-1400 14.7 8.6 14.0 16.3 16.9 16.6

-1500 15.8 9.1 13.3 16.3 17.0 17.4

-1600 16.5 9.5 12.8 16.3 16.9 16.8

-1700 15.3 11.7 13.2 16.4 16.8 16.8

-1800 16.4 11.6 16.7 16.5 16.7 16.4

-1900 16.4 12.0 16.9 16.4 16.6 16.5

-2000 16.7 12.7 17.0 16.4 16.6 16.5

-2100 16.8 13.7 17.0 16.3 16.6 16.5

-2200 16.8 16.0 16.9 16.3 16.5 16.7

-2300 16.6 16.8 16.9 16.2 16.2 16.3

-2400 15.5 16.5 17.1 16.3 16.5 16.6

-2500 15.2 16.5 16.0 16.3 16.5 16.5

-2600 15.7 16.6 16.9 16.2 16.5 16.5

-2700 16.4 16.5 16.9 16.1 16.6 16.5

-2800 16.8 16.6 16.9 16.2 16.5 16.4

-2900 16.8 16.7 16.7 15.9 16.2 16.3-3000 17.1 17.2 17.5 16.7 17.1 17.0


STEP 3. Assess Well Criticality Casing supported

Revisit well model

Insert corroded section/s

Review stress analysis


Account for the Well’s Slump

Well finds a new equilibrium

Significant load changes

May still be within limits

If slumped distance not known assume next string in is now structural.


Operational load sources

Weight of surface equipment – full stack up.

Thermal changes not to be underestimated! Any cold injections in particular

• All future lifecycle operations considered through to abandonment

Well kill operation adding 100 Te!


External load sources

Conductor supported wells

Include wave & current loading

Insert corroded section/s, define guides & clearance, soils

Well loads from static applied as distributed axial load in dynamic global model.

x

y

20" Surface Casing

30" ConductorProduction Deck

WellGuide Level 2 Weight

CentralisersMean Sea Level

Guide Level 3

Wave Loading

Guide Level 4

Guide Level 5

Guide Level 6

Guide Level 7

Mudline

P-Y Soil Springs

Surface Tree

Wellhead

Current

Profile


STEP 4. Corrective/Preventative Methods

Baseline PEC wall thickness & revisit at later date, corrosion problems not always obvious.

Corrosion inhibition

Rapeseed oil top up (N.Sea)

Biocide

Coatings / wraps (external)

Measure & record GAP and Wellhead elevation for significant events.

Low Severity



Stabilisation

Conductor guide reinstatement

Conductor & surface casing retro-fit centralisers

Increases fatigue life & reduces VME stress

Medium Severity

Conductor guide installation - Claxton Learn more at www.2hoffshore.com


Load transfer using shims/clamp

Conductor integrity?

Soil integrity?

D-Annulus access preserved

Grouting D-Annulus

Floating grout retainer for holed conductors

Access to D-Annulus lost

Corrosion inhibition over grouted interval

Hot or cold?

Restricting its movement not necessarily a good thing!

Medium Severity

Re-modelling required? Reinstate tension?



Platform Supported

No conductor integrity required

Platform strength – limited number of wells

Ideal for abandonment

Ideal to support well for repair work

Short term solutions



Reinforcing Conductors / Casings

Complex

Well supported / lifted during repair

Replacement

Full well integrity restored

Very complex

High Severity


Examples of CSim

Total Picture

Local Modelling of

Complex Geometries

Accurate Determination of Loads in Internal

Tubulars

Global Analysis of Riser and Conductor Systems

3

Wellhead fatigue assessment

for obsolete designs or complex interactions. Platform conductor

clamp design.

Platform conductor production mode

stability and fatigue assessment.

Identify design/remediation

requirements for centralisation.

Boundary Conditions Boundary

Conditions

Combining applications improves accuracy & moves closer to real life.


Summary The well model is invaluable to predict problems and catch the wells

EARLY.

Identify and repair critical wells APPROPRIATLY & COST EFFECTIVELY.

Prevent FURTHER CASULATIES and MONITOR

Well movement measurements during intervention & operations are invaluable. Is it moving as it should?

The wrong fix can cause other failures but if it’s not broken – don’t fix it!



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Documents

Ageing Platform Wells - 2H Offshore€¦ · 10 0 5 10 15 20 25 30 35 40 45. PEC reading [%] PEC reading [mm] Distance from top of Conductor [m] Platform XYZ - Well TRS-23 - 20" Casing