9. plug and abandonment (15.8.12)_revisjon til eksisterende

7/25/2019 9. Plug and Abandonment (15.8.12)_revisjon Til Eksisterende

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NORSOK Standard D-010 Rev. 4, August 2012

Page 1 of 35NORSOK standard

Below is a listing of the main changes

1. Definitions of suspension, temporary and permanent abandonment

2. Included more examples of well barrier schematics

3. Included illustrations for permanent abandonment scenarios (9.5.3)

4. Included shale formation as an annulus well barrier element (9.5.4)

5. Included flow charts for establishing permanent barriers (9.5.6 and 9.5.7)

6. Included requirements for XT removal

Table of Contents

9.1 General .......................................................................................................... 19.2

Well barrier schematics ................................................................................. 2

9.3 Suspension .................................................................................................... 2

9.3.1

General ................................................................................................... 29.3.2

Well barrier schematics ........................................................................... 3

9.4 Temporary abandonment .............................................................................. 59.4.1

General ................................................................................................... 5

9.4.2 Well barrier schematics ........................................................................... 69.5

Permanent abandonment ............................................................................ 15

9.5.1 General ................................................................................................. 159.5.2

Well barrier schematics ......................................................................... 17

9.5.3 Examples for different permanent P&A options .................................... 249.5.4

Formation as well barrier element ......................................................... 26

9.5.5 Sidetracking .......................................................................................... 26

9.5.6

Section milling to establish permanent barriers ..................................... 27

9.5.7

Alternative method to establish permanent barriers .............................. 29

9.5.8 Materials ............................................................................................... 309.6

Well control action procedures and drills ..................................................... 31

9.6.1 Well control action procedures .............................................................. 319.6.2

Well control action drills ........................................................................ 31

9.6.3 Well control requirements ..................................................................... 319.7

Suspension, plugging and abandonment design ......................................... 31

9.7.1 Design basis, premises and assumptions ............................................. 319.7.2

Load cases............................................................................................ 32

9.8 Other topics ................................................................................................. 32

9.8.1

Risks ..................................................................................................... 32

9.8.2

Removing equipment above seabed ..................................................... 33

9.9 Vertical Xmas tree (VXT) removal .............................................................. 349.10

Horizontal Xmas tree removal .................................................................. 35

9 Plugging, abandonment and suspension

9.1 General

This section covers requirements and guidelines for well integrity during plugging of wells inconnection with


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a) temporary suspension of well activities and operations,b) temporary or permanent abandonment of wells,c) permanent abandonment of a section of a well (side tracking, slot recovery) to construct a new

wellbore with a new geological well target.

The purpose of this section is to describe the establishment of well barriers by use of WBEs andadditional requirements and guidelines to execute this activity in a safe manner with focus on isolationof permeable formations/reservoirs/sources of outflow, both from each other in the wellbore, and fromsurface.

Requirements for isolation of formations, fluids and pressures for temporary and permanentabandonment are the same. However, choice of WBEs may be different to account for abandonmenttime, and ability to reenter the well or resume operations after temporary abandonment.

9.2 Well barrier schematics

Well barrier schematics (WBS) shall be prepared for each well activity and operation.

A final verified WBS for the well status upon completion of operations shall be in place.

Samples of well barrier schematics for selected situations are presented.

9.3 Suspension

9.3.1 General

Suspension of a production or injection well is defined as a well status, where the well is temporarilyplugged, XT is installed, and the well barriers are monitored.

Suspension of a well under construct ion or intervention is defined as a well status,where the well operation is suspended without removing the well control equipment.

Example: Disconnect due to WOW

Well barriers and WBE material(s) shall have sufficient integrity to meet the suspension period,including contingency. The suspended wellbore should be monitored throughout the suspensionperiod.

The following number of well barriers shall be in place to safely suspend the wellbore:

Suspension Formation

Two well barriers Potential source of inflow or reservoir exposed (hydrocarbons present)

One well barrier Formation with normal pressure (or less)


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9.3.2 Well barrier schematics

Suspended well, Hang off/disconnect of marine riser 9.3.2a

UPR

LPR

APR

Drilling

BOP

SSR

Well barrier elements WBEAC

table

Verification/Monitoring

Primary Well Barrier1. Fluid column 1 Time limited barrier

2.

3.

4.

5.

6.

7.

Secondary Well Barrier

1. Casing cement 22 Last casing

2. Casing 2

3. Wellhead 5

4. BOP 4

5.

6.

7.

Notes:

Well Integrity issues Comments/Notes

9.3.2a Suspension, Hang of f/Disconnect

of main riser

MPR


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Suspended well, completed well w ith deep set mechanical plug 9.3.2b

Well barrier elements SeeWBEAC

table


Primary Well Barrier1. Formation at 9 5/8

casing windown/a

2. 9 5/8 Productioncasing cement (up toprod packer)

22

3. 9 5/8 Productioncasing

4. (up to prod packer)

2

5. Production packer 76. Deepset plug 6

Secondary Well Barrier1. Formation at prod

packern/a

2. 9 5/8 Productioncasing cement (aboveprod packer)

22

3. 10 x 9 5/8Production casing

2

4. 10 Production

casing hanger with sealassembly

5

5. Tubing hanger withseals

10

6. Tubing hanger crownplug

11

7. X-mas treevalves/connector

31

8. X-mas tree body 31

Notes:


9.3.2b Suspended well, Completed well

with a deep set mechanical plug

13 3/8" csg Xxx

mTVD

10 3/4"-9 5/8" XOV

Xxx mTVD

20" csg XxxmTVD

PT

Reservoir

7" csg Xxx mTVD

Surface casing

Intermediate casing

9 5/8" csg Xxx mTVD

Production casing

Liner

DHSV


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9.4 Temporary abandonment

9.4.1 General

Temporary abandonment is defined as a well status in which the well has been temporarily pluggedwhere the BOP or XT has been removed, and the well barriers are not continuously monitored.

It shall be possible to re-enter temporary abandoned wells in a safe manner for the planned durationof the temporary abandonment.

In general the following number of well barriers shall be in place to safely re-enter the wellbore.

Temporary P&A Formation



For temporarily abandoned wellbores, the selected WBE material(s) shall have sufficient integrity tomeet the abandonment period times two.

Prior to temporary abandonment, the future plans for the well shall be documented.

Temporarily abandoned subsea wells shall be protected from external loads in areas with fishingactivities, or other seabed activities. For deep water wells, temporary seabed protection can beomitted if there is confirmation of no such activities in the area and at the depth of the abandonedseabed installations.

For temporary abandoned surface completed wells, it shall be possible to monitor the pressure in theA annulus and in the tubing.

For temporary abandoned subsea completed wells that are planned to be abandoned for more thanone year, a yearly program for monitoring and observation shall be established and implemented.

The pressure in the tubing and A annulus shall be monitored if a subsea completed well is planned tobe abandoned for more than one year or not tied back to a production facility. The followingrequirements are to be met:

Production/injection packer and tubing hanger is pressure tested.

Tubing is pressure tested.

The DHSV is closed and pressure/function tested.

All valves in the X-mas tree have been pressure tested with zero leak rate/function tested and

are closed. For wells with horizontal X-mas trees, the tree cap and tubing hanger crown plug shall be

pressure tested.

If monitoring is not practicable, an acceptable alternative may be to install a deep set well barrierelement plug.


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Temporary abandonment, reservoir exposed 9.4.2a


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Temporary abandonment, reservoir exposed - Casing 9.4.2b


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Temporary abandonment, no permeable formation exposed - Liner 9.4.2c

Well barrier elements WBEACtable


Primary Well Barrier Open hole

1. Cement plug 2428

Set as deep as possible withverified cement in casing annulus

2. Casing cement 223. Formation at the shoe na

Secondary Well Barrier Open hole

1. Casing cement 22

2. Casing cement or mechanicalplug

2428

Shallow plug

3. Liner top packer 43 Grade: V1

4. Formation

Well Integrit y issues Comments/Notes

9.4.2c Temporary abandonment, no

permeable formation exposed - Liner


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Temporary abandonment, no permeable formation exposed Casing 9.4.2d



Primary Well Barrier Open hole

1. Cement plug 2428

Set as deep as possible withverified cement in casing annulus

2. Casing cement 22

3. Formation at the shoe na

Secondary Well Barrier Open hole

1. Casing cement 22


2428

Shallow plug

3. Liner top packer 43 Grade: V1

4. Formation


9.4.2d Temporary abandonment, no

permeable formation exposed - Casing


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Temporary abandonment, non perforated well - Liner 9.4.2e


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Temporary abandonment, non perforated well - Casing 9.4.2f


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Temporary abandonment, impermeable formation w ith over pressure, non perforated9.4.2g


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Temporary abandonment, perforated well with BOP or XT removed - Liner 9.4.2h


table


Primary Well Barrier1. Casing (liner) cement 22

2. Casing (liner) 2 Liner above perforations.3. Liner top packer 43

4. Casing 2 Below production packer.

5. Production packer 7 50 m below TOC in casingannulus.

6. Completion string 25

7. Deep set tubing plug 6

Secondary Well Barrier1. Casing cement 22 Above production packer.

2. Casing 2 Common WBE, between liner toppacker and production packer.

3. Wellhead 5

4. Tubing hanger 10

5. Tubing hanger plug 11

Notes:


9.4.2h Temporary abandonment,

Perforated well with BOP or production

tree removed Liner


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Temporary abandonment, perforated well with BOP or XT removed - Casing 9.4.2i


table


Primary Well Barrier

1. Casing cement 22

2. Casing 2 Above perforations.

3. Production packer 7

4. Completion string 25

5. Deep set tubing plug 6


1. Casing cement 22 Intermediate casing.

2. Casing 2 Intermediate casing.

3. Wellhead 5

4. Tubing hanger 10

5. Tubing hanger plug 11


9.4.2i Temporary abandonment,

Perforated well with BOP or production

tree removed - Casing


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9.5 Permanent abandonment

9.5.1 General

This section covers requirements and guidelines for well integrity during permanent abandonment.

Permanently plugged wells shall be abandoned with an eternal perspective taking into account theeffects of any foreseeable chemical and geological processes.

The following number of well barriers to the external environment shall be fulfilled.

Permanent P&A Formation



The following individual or combined well barriers/isolations shall be a result of well plugging activities.

Name Function Requirement to depth position

Primary wellbarrier

First well barrier against apotential source of inflow. Toisolate a potential source ofinflow from flowing tosurface/seabed

The base of the barrier shall bepositioned at a depth where wellboreintegrity is higher than potentialpressure below, see 4.2.3.5.7 Testingof formation.

Secondarywell barrier

Backup to the primary wellbarrier, against a potentialsource of inflow.

As above.

Crossflow wellbarrier

To prevent flow betweenformations (where crossflow isnot acceptable). May alsofunction as primary well barrierfor the reservoir below.

As above.

Environmentalisolation plug*

To isolate the full cross sectionalwellbore. To prevent movementof wellbore fluids to theenvironment.

The selected position should bedocumented**.

*A well barrier may also function as an environmental plug.

**The environmental isolation plug should be of sufficient length to ensure containment.

Overburden formation should be assessed for abandonment requirements. Shallower permeablezones shall be plugged according to the same principle.

Multiple reservoir zones/perforations located within the same pressure regime can be regarded as onereservoir for which a primary and secondary well barrier shall be installed (see illustration).


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9.5.1.1 Permanent well barriers

Permanent well barriers shall extend across the full cross section of the well, include all annuli andseal both vertically and horizontally (see illustration). The well barrier(s) shallbe placed adjacent to an impermeable formation.

Casing cement shall be verified to ensure a vertical and horizontal seal. Ifcasing cement is verified by logging, minimum 30 m cumulative interval withacceptable bonding is required to act as a permanent external barrier. For theinternal permanent barrier requirement, refer to WBEAC 24. An internal WBEshall be positioned over the entire interval where there is a verified externalWBE (across all annuli).

A permanent well barrier should have the following characteristics:

a) Provide long term integrity (eternal perspective)b) Impermeablec) Non shrinkingd) Able to withstand mechanical loads/impacte) Resistant to chemicals/ substances (H2S, CO2 and hydrocarbons)f) Wetting to ensure bonding to steelg) Not harmful to the steel tubulars integrity

Steel tubulars are not an acceptable permanent WBE unless supported by cement or a pluggingmaterial with similar functional properties as listed above (internal and external).

Elastomer sealing components in WBEs are not acceptable for permanent well barriers.

Cement in the liner lap is accepted as a permanent WBE when pressure tested from above (beforeinstallation of liner top packer).

Removal of downhole equipment is not required as long as the integrity of the well barriers isachieved.

Control cables and lines shall be removed from areas where permanent well barriers are installed, ifthey can create vertical leak paths through the well barrier. Completions should be designed tofacilitate the setting of annular cement plugs as a well barrier.

When completion tubulars are left in the well and permanent well barriers are installed in the tubingand annulus, the position and integrity of the barriers shall be verified.


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If it can be documented that placing one continuous cement (with compensating measures ref to EAC24) plug is as reliable as two independent cement plugs to establish an internal barrier(s), this may beacceptable.


Permanent abandonment - Open hole 9.5.2 a

Casing/

No source

of outflow

Liner/

reservoir




1. Cement plug 24 Open hole

Or (Primary well barrier, lastopen hole)

1. Casing cement 22

2. Cement plug 24 Transition plug across casingshoe


1. Casing cement 22

2. Cement plug 24 Cased hole cement plug installedon top of a mechanical plug

Environmental Isolation plug

1. Cement plug 24 Cased hole cement plug

2. Casing cement 22 Surface casing


9.5.2a Permanent abando nment, open

hole


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Permanent abandonment Perforated well, tubing left in hole 9.5.2 b


table



1. Liner cement 22

2. Cement plug 24 Across and above perforations


1. Casing cement 22

2. Cement plug 24 Inside and outside of the tubing


1. Cement plug 24


Well Integrit y issues Comments/Notes

9.5.2b Permanent abandonment,

perforated well, tubing left in hole


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Permanent abandonment Perforated well, tubing removed 9.5.2 c


table



1. Liner cement 22

2. Cement plug 24 Across and above perforations


1. Casing cement 22

2. Cement plug 24 Across the liner plug.


1. Cement plug 24



9.5.2c Permanent abandonment,

perforated well, tubing removed


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Permanent abandonment, Multi bore with slotted liners or sand screens with plug 9.5.2d



Primary Well Barrier - Reservoir

1. Cement plug 22 Across and above theperforations

Secondary Well Barrier - Reservoir1. Casing cement 22

2. Casing cement 2428

Across the liner plug


1. Cement plug 24



9.5.2d Permanent abando nment,

multibore with slotted liners or sand

screens with pl ug


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Permanent abandonment, Multi bore with slotted liners or sand screens without plug 9.5.2e



Primary Well Barrier Reservoir

1. Cement plug 22 Across and above theperforations

Secondary Well Barrier Reservoir1. Casing cement 22


2428

Across the liner plug


1. Cement plug 24



9.5.2e Permanent abando nment,

multibore with slotted liners or sand

screens without plug


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Permanent abandonment, Slotted liners in multiple reservoirs 9.5.2f



Primary Well Barrier1. Cement plug 24 Through liner and across casing

shoe / open hole

Secondary Well Barrier1. Casing cement 22

2. Cement plug 24 Across the liner top


1. Cement plug 24 Squeezed into perforatedcasing/annulus above potentialreservoir


1. Casing cement 22

2. Cement plug 24


1. Cement plug 24 Cased hole



9.5.2f Permanent abandonment, Slotted

line in multiple reservoirs


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Permanent abandonment, Slotted liners in multiple reservoirs Intermediate casing cemented to

previous casing shoe 9.5.2g



Primary Well Barrier1. Cement plug 24 Through liner and across casing

shoe / open hole

Secondary Well Barrier1. Casing cement 22

2. Cement plug 24 Across the liner top


1. Cement plug 24 Squeezed into perforatedcasing/annulus above potentialreservoir


1. Casing cement 22

2. Cement plug 24

Environmental Isolation

1. Cement plug 24 Cased hole



9.5.2g Permanent abandonment, Slotted

line in mult iple reservoirs Intermediate

casing cemented to previous casing

shoe


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9.5.3 Examples for different permanent P&A options

The following illustrations show permanent P&A options.

Example A

The last open hole section of a wellbore can be abandoned permanently by setting an open hole

cement plug across/above the reservoir and an additional cement plug from the open hole into the

casing (the minimum requirements are illustrated in figures below):

The requirement is to have sufficient wellbore (formation) integrity at the base of both well barriers.

Secondary

100 m

Verification:

Tag OH plug.

P&A open hole and inside

casing plugs

Plug lengths:

minimum 100 m

min50m

min30mo

fverifiedloggedcement

min50m

Primary

100 m

Verification:

Pressure test plug

inside casing

min50mi

nOH

andmin50mi

nsidecsg


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Example B

The last open hole section of a wellbore or a perforated casing/liner can be abandoned permanentlyby setting two back to back cement plugs from the reservoir (or as close as possible to the reservoir),providing the casing cement is verified in the annulus.

The internal cement plug lengths shall cover the cumulative logged interval in the annulus.

Reservoir/perm.

fm with

overpressure

Secondary

50 m

Verification:

Tag and

pressure test

primary plug

50 m inside

casing

P&A two back to back cement

plugs

2 x 30 m verified

logged cement

Primary

100 m

Verification:

Volume control(Set on pressure

tested fundament)


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Example C

A wellbore can be abandoned permanently by setting a mechanical plug to serve as a fundament for asingle cement plug.

The internal cement plug length shall cover the cumulative logged interval in the annulus

Primary

Verification:

Pressure tested

fundament

P&A Single cement plug

with mechanical plug

foundation

Secondary

Reservoir/

perm. fm with

overpressure

Verification:

Tag cement plug2 x 30 m

verified

logged cement

Formation as annulus well barrier element

Bonded and impermeable in-situ formation (e.g. shale, salt) is accepted as an annulus well barrierelement if qualified according to WBEAC 52 (Shale Formation).

9.5.4 Sidetracking

The original wellbore should be permanently abandoned prior to a side-track/ slot recovery. A wellbarrier can be shared to function as well barrier for more than one well bore.


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9.5.5 Section milling to establish permanent barriers

The following method can be applied when section milling is required to establish well barriers.

Log casing annulus

to verify bonded

formation/cement

Verified with

sufficient length to

act as barrier?

Sufficient length

with bond to act as

foundation?

Place cement plug

from fundament

and minimum 50m

across window

Install and test

mech plug in

bonded area

WOC and tag

Place second

cement plug from

top of first plug

and 50 m into

casing

WOC and leak

test to 70 bar

above leak off

Yes No

Yes

Install and test

mech plug in

casing as close as

possible to source

of inflow

Perforate and performlow pressure cement

squeeze to establish an

external fundament

(other means to

establish fundament

can be used)

Section mill and

underream/wash to

expose formation

No

Mill 100 m Mill > 50 m

Evaluate situation.

Consider further section

milling

Place cement plug

from fundament to

50 m into casing

WOC and leak

test to 70 bar

above leak off

Establish

secondary barrier

in same manner

as primary

(another 50 msection mill above

bonded area etc)

No

Yes

Primary and

secondary barriers

established

Re-establishing

annulus barrier not

necessary

Establish internal

barrier


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Example

For wells with poor casing cement or no access to the last open hole section,section milling (removal of casing) is an alternative method for placing cementin contact with formation to form permanent barriers.

Milling window:

minimum 100 m

P&A section milling

Verification:

Tag

Verification:

Pressure test

min 50 m

min 50 m

min 50 m Milling window:

minimum 50 m

Verification:

Pressure test

cement plug

inside casing

min 50 m

max 50 m

min 50 m

min 50 m

Reservoir/

perm. fm with

overpressure

Reservoir/

perm. fm with

overpressure

Verification:

Pressure test

cement plug

inside casing

Milling window:

minimum 50 m


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9.5.6 Alternative method to establish permanent barriers

The use of alternative methods to establish the barriers shall be verified and documented.

Log casing annulus

to verify bonded

formation/cement

Verified with

sufficient length to

act as barrier?

Re-establishing

annulus barrier not

necessary

Sufficient length

with bond to act as

foundation?

Establish internal

fundament if

required

Yes No

Yes

Install and test

mech plug in

casing as close as

possible to source

of inflow

Perforate and perform

low pressure cement

squeeze to establish an

external fundament

(alternative methods to

establish a fundament

can be used)

Establish annulus

communication (perforate

interval)

No

Place continuous plug from

fundament to 50m above top perf

Establish internal

barrier

Circulate the casing annulus to

create a clean, water-wet interval

for bonding

Establish secondary barrier in

same manner as primary

Primary and

secondary barriersestablished

Squeeze cement perforations

Leak test to 70 bar above leak off

Drill or clean out and re-log to

confirm 50 m annulus seal

Set internal cement plug across

interval with annulus seal.

ALTERNATIVE METHODS


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Example

For wells with poor casing cement or no access to the last open hole section, analternative method for placing cement in contact with formation to form permanentbarriers can be used.

External verification may be omitted once a geological specific interval track record isestablished and documented.

Min 50 m

Min 50 m

Min 50 m

Internal Verification:

Tag and pressure test

Internal Verification:

Pressure test

External Verification:

Logging

External Verification:

Logging

Fundament:

Internal and external

required

P&A alternative method

9.5.7 Materials

The materials used in well barriers for plugging of wells shall withstand the load and environmentalconditions the well barriers may be exposed to for the planned abandonment period. The suitability ofthe selected plugging materials shall be verified and documented. Degradation of the casing shouldbe considered.


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9.6 Well control action procedures and drills

9.6.1 Well control action procedures

The following table describes incident scenarios in which well control action procedures should beavailable (if applicable) to deal with the incidents should they occur. This list is not comprehensive and

additional scenarios may be applied based on the actual planned activity.

Item Descrip tion Comments

1. Cutting of casing. Trapped gas pressure in casingannulus.

2. (SSW) Pulling casing hanger seal assembly. Trapped gas pressure in casingannulus.

3. Re-entry of suspended or temporary abandonedwells.

Account for trapped pressure underplugs due to possible failure ofsuspension plugs.

9.6.2 Well control action drills

The following well control action drills should be performed:


1. Pressure build-up, or lost circulation in connection witha cutting casing operation.

To verify crew response in applyingcorrect well control practices.

2. Loss of well barrier while performing an inflow test.

9.6.3 Well cont rol requirements

Cutting/perforating the casing and retrieving seal assemblies shall be performed with active pressurecontrol equipment in place to prevent uncontrolled flow from annuli between casings and into thewell/riser

9.7 Suspension, plugging and abandonment design

9.7.1 Design basis, premises and assumptions

All potential sources of inflow shall be documented.

All well barrier elements used for plugging of wells shall withstand the load and environmentalconditions they may be exposed to for the abandonment period.

The following information should be gathered as a basis of the well barrier design and abandonment:

a) Well configuration (original and present) including depths and specification of permeableformations, casing strings, cement behind casing status, well bores, side-tracks, etc.

b) Stratigraphic sequence of each wellbore showing reservoir(s) and information about theircurrent and future production potential, where reservoir fluids and pressures (initial, currentand in an eternal perspective) are included.

c) Logs, data and information from cementing operations in the well.


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d) Formations with suitable well barrier element properties (i.e. strength, impermeability, absenceof fractures and faulting)

e) Specific well conditions such as scale build up, casing wear, collapsed casing, fill, H2S, CO2,hydrates, benzene or similar issues.

The design of well barriers consisting cement or alternative materials should account for uncertainties

relating to

f) downhole placement techniques,

g) minimum volumes required to mix a homogenous slurry,

h) surface volume control,

i) pump efficiency/ -parameters,

j) contamination of fluids,

k) shrinkage of cement or plugging material

l) centralisation.

9.7.2 Load cases

A combination of the functional and environmental loads shall be designed for.

For permanently abandoned wells, the specific gravity of well fluid accounted for in the design shall asa maximum be equal to a seawater gradient.

The following load cases should be applied for the abandonment design:


1. Minimum depth of primary and secondary well

barriers for each reservoir/potential source of inflow,taking the worst anticipated reservoir pressure forthe abandonment period into account.

Not shallower than the wellbore

(formation) integrity at these depths.Reservoir pressure may for permanentabandonment revert to initial/virginlevel. It should take into account re-development scenarios or gas storageif applicable.

2. Pressure testing of casing plugs. Criteria as given in WBEAC 24.

3. Burst pressure limitations on casing string at thedepths where temporary abandonment plugs areinstalled.

Cannot set plug higher than the burstrating allows (less wear factors).

4. Collapse loads from seabed subsidence or reservoircompaction.

The effects of seabed subsidenceabove or in connection with the

reservoir shall be included.

9.8 Other topics

9.8.1 Risks

Design and operational risks shall be assessed. Typical risk could include:a) pressure and wellbore (formation) integrity uncertainties,b) time effects:

long term development of reservoir pressure deterioration of materials used

sagging of weight materials in well fluidsc) scale in production tubing,d) H2S or CO2,


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e) release of trapped pressure,f) unknown status of equipment or materials,g) environmental issues.

9.8.2 Removing equipment above seabed

For permanent abandonment wells, the wellhead and casings shall be removed below the seabed.

The cutting depth shall be sufficient to prevent conflict with other marine activities. Local conditionssuch as soil and seabed scouring due to sea current should be considered. For deepwater wells, itmay be acceptable to leave or cover the wellhead/structure.

Mechanical or abrasive cutting is the preferred method for removal of the casing/conductor at seabed.

Use of explosives to cut casing/conductor is acceptable only if measures are implemented (Example:directed/ shaped charges providing upward and downward protection) which reduces the risk tosurrounding environment to the same level as other means of cutting.

The location shall be inspected to ensure no other obstructions related to the drilling and well activitiesare left behind on the sea floor.


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9.9 Vert ical Xmas tree (VXT) removal

The table below describes well barrier requirements when removing a VXT.

Fluid Possible tomonitor primary

well barrier?

Primary well barrierelement

Secondary well barrierelement

Compensatingmeasures

Light fluid(under-balanced)

Yes (downholepressure gaugeor tubing toannuluscommunication)

Deep set mechanicalbridge plug

Inflow testedDHSV and dropprotection device accepted ifDHSV has zeroleakage, or

a BPV/tubinghanger plug, or

a shallow setmechanical bridgeplug

Status of primarywell barrier to bemonitored at alltimes on DHPGor a-annuluspressure

No Deep setmechanical bridgeplug



Inflow testedDHSV ascompensatingmeasure due tonot able tomonitor primarybarrier

Heavyfluid(over-balanced)

Yes (tubing toannuluscommunication)

Deep setmechanical bridgeplug and brine/mudabove plug, or

Kill pill and brine or

kill mud fromperforations/screento surface




Fluid level orapplied pressureto be monitoredon A-annulus

No Deep setmechanical bridgeplug and brine/mudabove plug




No Kill pill and brine orkill mud fromperforations/screento surface



Inflow testedDHSV ascompensatingmeasure due tonot able tomonitor primarywell barrier


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9.10 Horizontal Xmas tree removal

A deep set plug shall be installed.

The production tubing and production annulus shall be displaced to kill fluid. Specific gravity of the kill

fluid shall give an overbalance with a safety margin at plug depth, prior to pulling the productiontubing.

When the tubing is removed, a shallow plug shall be installed in production casing prior to removal ofthe XT.

9. plug and abandonment (15.8.12)_revisjon til eksisterende

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