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Intervention Barriers
• A barrier is defined as a means of containing wellbore pressure and fluids.
• Two effective barriers are required for most intervention operations.
• Consider when barriers are effective (and when they are not) and how to back them up for safety.
• Must be rated to the maximum pressure that can be encountered.
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Common Barriers • Kill weight fluid column (not just a fluid column) – monitored and
tested • Pipe rams when pipe is in the well • Blind/Blind-Shear when no pipe is in the well • Master valve when pipe is not in the well • CT Flapper valves (dual flappers = one barrier) • Stuffing box/Stripper Rubber • Downhole plugs • Grease seal/ram for braided line (both are one barrier)
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1. Nipple
Down
Tree
2. Nipple
Up BOP
Barriers
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3-2006
TEST LINETEST LINE
Flanged Choke
Ported w/1-1/2”
NP & Threads
& 2- 10K Needle Valves
Hammer Union
& Bull Plug
3-2006
TEST LINETEST LINE
3-20063-2006
TEST LINETEST LINE
Flanged Choke
Ported w/1-1/2”
NP & Threads
& 2- 10K Needle Valves
Hammer Union
& Bull Plug
What’s Left?
1. Hook up test and kill
lines.
2. Test.
Barriers – last steps
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Kill Weight Fluid
KWF = Formation Pore Pressure (psi) / (0.052 * TVD to mid perfs (ft))
where: KWF = kill weight fluid in ppg
TVD
The kill weight fluid must occupy both
the annulus and the tubing with no
voids or other fluids involved.
If the density and level of the fluid are
not monitored, can the fluid be an
effective barrier?
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Difference between Surface and Downhole Barriers
• A surface barrier prevents escape of fluids from the well.
• A downhole barrier may also prevent cross-flow between formations.
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The barrier during drilling is a well
control barrier that has both hydrostatic
and mechanical control points.
A column of kill weight fluid, monitored
and tested, is a common active barrier.
Multiple barriers
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During wireline intervention, the
control method is pressure
control with two or more
barriers.
The barriers for wireline include:
1. Grease or oil seal on the wire
(for dynamic sealing);
2. Packoff for static application
3. Blind/Shear rams
4. Master valve (can cut some
wire, but poses a risk of valve
damage).
Double Bariers
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Barriers for Intervention with
Coiled Tubing
Barriers include:
1. Stuffing Box
2. Coiled Tubing BOP
3. Annular Preventer (for
sealing around BHA string)
4. Pipe ram below circulating
cross or Tee.
5. Master Valves – when CT and
BHA are above the top
Master Valve.
Stacked Barriers
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Barriers for Producing Wells – usually only
one barrier for many areas:
1. Almost all flow/gathering lines,
separators and pipelines.
2. The flow cross, choke body and other
areas above the tubing hanger
3. Below the tubing hanger for gas lift
supply
4. At any open shoe with gas lift supply
5. Uncemented casing below the packer
Producing Wells – One Barrier
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Live Well Workovers
• Top Hole - plug (WL or CT) set at or below packer - top of well is isolated.
Used for:
press test
pickle/cleanout
tubing replacement
fluid unload/swap
equalizing plug www.GEKEngineering.com 11
Typical Conditional Barriers
• Considered a barrier during certain operations but not at other times.
• Examples: – Pipe rams – barrier only when pipe is in the well
– Blind ram, master valve, stripper rubber – barrier only when pipe is out of the well
– Braided line rams – barrier only with grease injection
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Layout for a CT BOP
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Ram blocks
Lower left – slip blocks
Lower Right – seal blocks
Upper Right – shear or
cutter blocks
Ram Internals
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CT BOP w/ kill port
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Greased ram section in a BOP prior to the job. Effect of excess grease?
Rams are heavily greased – Cleaning?
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Open ram
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CT Crushed by ram closure – now, how do you recover it?
Rams for CT must:
1. Center the CT in the BOP body
2. Center the CT in the ram element www.GEKEngineering.com 18
BOP accumulator – pressure
source
Accumulator
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What if the flow cross leaks? Control point?
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No secondary control below a flow cross
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One approach to control
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An effective
BOP rig-up.
Note dual valves
and flow control
below the flow
cross.
Stacked BOP
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Develop Both Sides?
May be practical for high risk wells.
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Unusual Cases
• When running a BHA that cannot be sealed with a pipe ram or cut with a blind shear. Is a special barrier needed for the BHA?
• When changing the elements on a ram or stripper rubber. Is a backup needed?
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The Two Barrier Rule
• Barriers may be the same in some instances.
• Both must be capable of controlling the full well pressure.
• Many barriers are conditional – may need back-up.
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Some Special Cases
• Snubbing or hydraulic workover – The two (minimum) pipe rams are barriers, but a blind-shear is required for a second barrier while pipe is in the well.
• What is needed when an pipe ram element has to be changed?
• A second blind or blind-shear or master valve or other device is required when pipe is out of the well.
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Hydraulic Workover Units
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Pipe seal
elements
Pipe ram elements
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Hydraulic
workover unit
showing the
gas bypass tube
between pipe
rams.
Hydraulic Workover BOP set
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Special cases, continued
• Large BHA or BHA that cannot be cut.
– Annular preventer?
– Downhole valves (SSSV as a barrier????) – SSSV’s are not a good barrier if an object can be dropped from the tool. A dropped object can breach/break the seal offered by flapper type SSSV.
– Pressure operated downhole valves
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Special cases, continued
• Fracturing Tree Saver
– Hydraulic deployment
– Second set of valves – temporarily replaces wellhead valve control
– Stinger with seal isolates and “locks-out” wellhead valves
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Tree Saver – isolates existing wellhead with hydraulically
deployed stinger with external seals and second set of valves.
Frac Iron
Connection
Remote operated
master valve Manual operated
master valve
Hydraulic cylinders
Mandrel or stinger – with
seals on exterior
Hydraulic pistons
Existing master
valve on well
Well master
valve is closed
Vent
Valve
Tree saver inserted
and locked down.
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Special Cases, continued
• What is stability of the barrier?
– To outgassing (seal face failure)
– To high or low temperatures (does it weaken barrier?)
– To corrosion (components weakened by attack?)
– To erosion – erosion of sealing surfaces
– To high or low pressure spikes
– To high or low tensile loads
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Special Example - Inflatable Packers
• Are they barriers?
• What is the reliability?
• Do they stay put?
• Has a great deal to do with how much they are expanded and where they are placed. – Good reliability when set in pipe
– Good reliability when placement “slide” is short (less than 1000 ft)
– Good reliability when expansion from initial to set is less than 2x.
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Quiz - Barriers
1. What type of equipment must not be sheared in a well control attempt?
2. What type of event or action may render the following barriers useless?
a. Blind ram, no pipe in the hole.
b. Pipe ram w/ pipe in the hole.
c. Stripper rubber on Coiled Tubing.
d. Grease injector with E-line in the well.
e. Flappers on coiled tubing.
3. For each challenge in problem 2, what is a possible solution?
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Quiz – Barrier Failure Recovery from Problem #2.
Failure Type Cause Recovery
Blind Ram, face seals destroyed.
Pipe Ram, w/ pipe in hole, no seal.
Stripper rubber leaking on CT
Grease leaking on E-line grease injector, not holding pressure.
Flappers not preventing backflow on cleanout.
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