practical intervention barriers -...

Practical 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.

3/14/2009 1George E. King Engineering

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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


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Flanged ChokePorted w/1-1/2”NP & Threads& 2- 10K Needle Valves

Hammer Union& Bull Plug 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.


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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.


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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).


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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.


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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


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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 plug3/14/2009 11

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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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Ram blocks

Lower left – slip blocks

Lower Right – seal blocks

Upper Right – shear or cutter blocks


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Greased ram section in a BOP prior to the job. Effect of excess grease?


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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


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BOP accumulator – pressure source


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An effective BOP rig-up. Note dual valves and flow control below the flow cross.


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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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Pipe seal elements


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Hydraulic workover unit showing the gas bypass tube between pipe rams.


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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.3/14/2009 35George E. King Engineering

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Quiz - Barriers1. 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 RecoveryBlind Ram, face seals destroyed.Pipe Ram, w/ pipe in hole, no seal.Stripper rubber leaking on CTGrease leaking on E-line grease injector, not holding pressure.Flappers not preventing backflow on cleanout.


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