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Barrier Philosophy for Wells on Gas lift
and
Ways of Reducing HSE Risks
Alan Brodie Feb 2011
For more info visit www.ptc.as
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Introduction
Gas Lifted Well Integrity Management
Incremental HSE risks
Case histories
The impact of getting it wrong
Solutions to incremental HSE risks
Image used with the permission of J Bellarby
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Oil and Gas Well Integrity Management
Basic Requirement
Risk of hydrocarbon release from a well is ALARP
(As Low As Reasonably Practicable)
Which means using:
Best available equipment Current industry best practices
To achieve this most OPCOs usually adopt:
Double independent barrier pressure containment envelope
In natural flow example shown:
Primary barrier outlined in red Secondary barrier outlined in blue
With Acceptance criteria defined for each element e.g:
ISO 13679 procedures for testing tubing connections
Leak criterion for gas: 9 cc/15 min
Image used with the permissi
on of J Bellarby
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Gas Lifted Well Integrity ManagementKey differences # 1 ( tubing integrity)
With many gas lift valves
Primary well containment barrier is compromised
ISO 17078-2 Flow control devices for side-pocket mandrels
These devices are designed and intended to prevent reverse flow
through a flow control device. They are not designed nor intended to
provide a tight shut-off pressure safety seal or to be a part of thesafety system.
Allowable leak rate
6883 ml/10 mins
Compare this to acceptance criteria for packers
ISO 14310-- Downhole equipment -- Packers and plugs
Allowable leak rate 20cc /10 mins
ISO 14310
Image used with the permission of J Bellarby
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Gas Lifted Well Integrity Management
Key differences # 2 ( High pressure gas inventory)
High pressure gas in tubing / production casing annulus Question:
What precautions are taken at well sites re gas bottles:
Store safely away from areas with:
High risk of dropped objects
Potential sources of radiant heat
Carefully manage logistic and numbers
Potential volume of gas in annulus of each well:
Equivalent of > 1000 industrial gas bottles
Even where DHASVs used typically >100
Lift gas lines / valves from HP header to annulus:
Pass thru area with Relatively high risk of dropped objects
Many potential sources of radiant heat
Other risks associated with leakage from inner to outer annulus
Are production casing threads gas tight?
Image u
sed with the permission of J Bellarby
The first
gas bottle
explodes
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Gas Lifted Well Integrity ManagementGetting it wrong (1)
Piper Alpha Disaster N Sea 1988:
Gas lift was widely used,
Wasnt the root cause but it exacerbated the situation
SCSSSVs generally closed
But Gas lift check valves didnt
Gas lift lines parted between isolation valve and wellhead
Due to radiant heat from nearby fires
Wells flowed naturally via annulus
NB It appears the wells structural integrity
was relatively unaffected despite the
severity of the incident
Image used with the permission of J Bellarby
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Gas Lifted Well Integrity ManagementGetting it wrong (2)
Outer Annulus Pressure build up
Onshore gas lifted well shut in
Lift gas leaked from the inner to the outer annulus
Outer annulus pressure built up to lift gas pressure (1700-1950 psi) Well restarted and heated up by 76 F
Trapped pressure increased to 7700psi
Outer annulus casing ruptured
Flying debris damaged the HP gas line
Contents of inner annulus vented and ignited
Question
How easily could this happen on your wells?
#1 Source of info: www.wellintegrity.net
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Gas Lifted Well Integrity ManagementReducing the HSE risks (1) ( tubing integrity)
Employ qualified well barrier gas lift valves
Operating Valves
Unloading Valves
Tested to the same allowable leak rate as packers etc
Erosion test the valves to ensure:
They will remain well barrier valves for the life of well
Not just to pass a factory acceptance test (FAT)
Image used with the permission of J Bellarby
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Gas Lifted Well Integrity ManagementReducing the HSE risk (High pressure gas inventory)
Down-hole Annulus Safety Valves (DH ASVs)
Introduced after Piper Alpha in some parts of world
To reduce the volume of gas topsides is exposed to
Still typically equivalent of >100 gas bottles !!
Shallow set dual path packers
Integral check valve or sliding sleeve
Usually not designed to be gas tight
Always requires a full workover to replace on failure
DH ASV reliability issues Apparently many wells closed in due to failed DH ASVs
Problems with packer technology in thermal cycling
Integral check valve reliability challenges
Reputedly often difficult to retrieve
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Gas Lifted Well Integrity ManagementReducing the HSE risk (High pressure gas inventory)
PTCs fresh approach to DH ASVs
Dual Packer technology designed for thermal cycling 4 110 deg C
Client supplied SCSSSV attached above
ISO-14310-V1 equivalent leak rate on gas side
Solid body compact packer design
Up to 10 control lines pass-through
Single trip retrieval using Sondex cutter
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Gas Lifted Well Integrity ManagementReducing the HSE risk (HP lift gas inventory)
Eliminate the potential for annulus venting
Using Surface Annulus Safety (SAS) valve
Set in the wellhead VR profile
Employs PTC Safelift GLV check valve design
No erosion across metal / metal seal faces Performance exceeds that delivered by DH ASV
Valves tested to API 6A PSL 3G PR2
Fire tested to API 6FB and API 6FD
Achieving V0 with gas as test medium
Valves replacable without workover
Image used with the permission of J Bellarby
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Gas Lifted Well Integrity ManagementReducing the HSE risk (HP lift gas inventory)
Actuator module holds check valve open throughout life
Protecting seal faces from chattering
Modular design facilitates actuator detachement
In case of annulus line damage
Leaving check valve intact in wellhead
Image used with the permission of J Bellarby
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Gas Lifted Well Integrity ManagementReducing the HSE risk (HP lift gas inventory)
> 250 SAS valves installed
In use in GOM and N Sea
Gas lifted wells with failed DH-ASVs previously had to be closed in
Awaiting workover
Now permitted to remain on stream If SAS valves are installed
And if well barrier accredited gas lift valves are used
Increasingly recognised by OPCOs as:
required for achieving ALARP risk in gas lifted wells
Some OPCOs even using them in combination with DH ASVs Their interpretation of ALARP
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Gas Lifted well integrity MgtReducing the HSE risk (trapped annulus)
Automated annulus pressure management Unique VR Plug / sensors can be installed on all annuli
Continual annulus P&T measurement
Wireless (HART protocol) / wired link to control room
Wireless module detaches safely under impact Leaving VR plug / sensor in wellhead
Annuli can be bled down automatically via M-SAS valves
Before closing again to ensure well integrity
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Gas Lifted well integrity mgtReducing the HSE risk
Automated annulus pressure bleed down PTC gas lift valve derivatives
One way (outer to inner) valves
Pre set opening pressures (MAASP)
Installed in special casing pups below wellhead New wells only
Not just for gas lifted wells
Ideal for subsea wells
Typically casings are not cemented into previous shoe track To provide option for pressure to bleed off into formation
Deploying annulus bleed valves would reduce this HSE risk
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Conclusions
HSE risks in well completions are managed to be ALARP
Gas lift introduces significant additional HSE risks cf any other lift method:
GLVs can be primary well containment envelope weak link
Enormous inventory of high pressure gas introduced to hazardous area
Potential for lift gas leakage into outer annuli
New technologies developed to address these concerns:
Well barrier gas lift valves and unloading valves
Wellhead VR profile actuated Surface Annulus Safety (SAS) valves
ISO-14310-V1 equivalent leak rate DH ASVs Wellhead VR profile pressure temperature sensors
Trapped annulus pressure relief valves
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Final thought
Lets do a little role playing exercise :
Youre sat in the office next month and your phone rings
Its your CEO on the line
He tells you he has been invited to a meeting with the government
To discuss a recent safety incident involving a gas lifted well
He asks you
Can I confidently say our designs ensured the risks were ALARP
Whats your answer .................
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Feb. 2011 2011 Gas-Lift Workshop 18
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Feb. 2011 2011 Gas-Lift Workshop 19
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