9. plug and abandonment (15.8.12)_revisjon til eksisterende
TRANSCRIPT
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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
Verification/Monitoring
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:
Well Integrity issues Comments/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
Two well barriers Potential source of inflow or reservoir exposed (hydrocarbons present)
One well barrier Formation with normal pressure (or less)
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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9.4.2 Well barrier schematics
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
Verification/Monitoring
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
Well barrier elements WBEACtable
Verification/Monitoring
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
2. Casing cement or mechanicalplug
2428
Shallow plug
3. Liner top packer 43 Grade: V1
4. Formation
Well Integrity issues Comments/Notes
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
Well barrier elements SeeWBEAC
table
Verification/Monitoring
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:
Well Integrity issues Comments/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
Well barrier elements SeeWBEAC
table
Verification/Monitoring
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
Secondary Well Barrier
1. Casing cement 22 Intermediate casing.
2. Casing 2 Intermediate casing.
3. Wellhead 5
4. Tubing hanger 10
5. Tubing hanger plug 11
Well Integrity issues Comments/Notes
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
Two well barriers Potential source of inflow or reservoir exposed (hydrocarbons present)
One well barrier Formation with normal pressure (or less)
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.
9.5.2 Well barrier schematics
Permanent abandonment - Open hole 9.5.2 a
Casing/
No source
of outflow
Liner/
reservoir
Well barrier elements WBEACtable
Verification/Monitoring
Primary Well Barrier
1. Cement plug 24 Open hole
Or (Primary well barrier, lastopen hole)
1. Casing cement 22
2. Cement plug 24 Transition plug across casingshoe
Secondary Well Barrier
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
Well Integrity issues Comments/Notes
9.5.2a Permanent abando nment, open
hole
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Permanent abandonment Perforated well, tubing left in hole 9.5.2 b
Well barrier elements SeeWBEAC
table
Verification/Monitoring
Primary Well Barrier
1. Liner cement 22
2. Cement plug 24 Across and above perforations
Secondary Well Barrier
1. Casing cement 22
2. Cement plug 24 Inside and outside of the tubing
Environmental Isolation plug
1. Cement plug 24
2. Casing cement 22 Surface casing
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
Well barrier elements SeeWBEAC
table
Verification/Monitoring
Primary Well Barrier
1. Liner cement 22
2. Cement plug 24 Across and above perforations
Secondary Well Barrier
1. Casing cement 22
2. Cement plug 24 Across the liner plug.
Environmental Isolation plug
1. Cement plug 24
2. Casing cement 22 Surface casing
Well Integrity issues Comments/Notes
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
Well barrier elements WBEACtable
Verification/Monitoring
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
Environmental Isolation plug
1. Cement plug 24
2. Casing cement 22 Surface casing
Well Integrity issues Comments/Notes
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
Well barrier elements WBEACtable
Verification/Monitoring
Primary Well Barrier Reservoir
1. Cement plug 22 Across and above theperforations
Secondary Well Barrier Reservoir1. Casing cement 22
2. Casing cement or mechanicalplug
2428
Across the liner plug
Environmental Isolation plug
1. Cement plug 24
2. Casing cement 22 Surface casing
Well Integrity issues Comments/Notes
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
Well barrier elements WBEACtable
Verification/Monitoring
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
Primary Well Barrier
1. Cement plug 24 Squeezed into perforatedcasing/annulus above potentialreservoir
Secondary Well Barrier
1. Casing cement 22
2. Cement plug 24
Environmental Isolation plug
1. Cement plug 24 Cased hole
2. Casing cement 22 Surface casing
Well Integrity issues Comments/Notes
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
Well barrier elements WBEACtable
Verification/Monitoring
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
Primary Well Barrier
1. Cement plug 24 Squeezed into perforatedcasing/annulus above potentialreservoir
Secondary Well Barrier
1. Casing cement 22
2. Cement plug 24
Environmental Isolation
1. Cement plug 24 Cased hole
2. Casing cement 22 Surface casing
Well Integrity issues Comments/Notes
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:
Item Descrip tion Comments
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:
Item Descrip tion Comments
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
a BPV/tubinghanger plug, or
a shallow 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
Inflow testedDHSV and dropprotection device accepted ifDHSV has zeroleakage, or
a BPV/tubinghanger plug, or
a shallow setmechanical bridgeplug
Fluid level orapplied pressureto be monitoredon A-annulus
No Deep setmechanical bridgeplug and brine/mudabove plug
Inflow testedDHSV and dropprotection device accepted ifDHSV has zeroleakage, or
a BPV/tubinghanger plug, or
a shallow setmechanical bridgeplug
No Kill pill and brine orkill mud fromperforations/screento surface
a BPV/tubinghanger plug, or
a shallow setmechanical bridgeplug
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.