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WELL BARRIERS



WELL BARRIERS

Aim:

• To fully understand Well Barrier philosophy in Drilling,Coring & Tripping operations.

Objectives:

• State the Primary Barrier in normal Drilling operations.• Identify Secondary Barrier elements.

• Describe a Barrier envelope.

• List what Barrier test documentation should contain.



Well Barriers

Primary well barrier:

• This is the first object that prevents flowfrom a source.

Secondary well barrier:

• This is the second object that preventsflow from a source.



What are Well Barriers

• Well barriers are envelopes (something that

surrounds or encloses something else) of one ormore dependent WBE’s (well barrier elements)

to prevent fluids or gases from flowing

unintentionally from a formation, into anotherformation or back to surface.

• Well barrier(s) shall be defined prior to

commencement of an activity or operation by

description of the required WBE’s to be in place

and the specific acceptance criteria.



Well Barrier Element Examples

1. Fluid Barriers2. Casing and Cement

3. Drill string

4. Drilling, Wireline, Coil Tubing, Workover BOP’s5. Wellhead

6. Deep set tubing plug

7. Production Packer 8. Stab-in Safety Valves

9. Completion String

10. Tubing Hanger

* Barrier elements in red denote other operations in a well



Well Barriers Drill ing, Coring, Tripping

Primary well barrier:This is the first object that

prevents flow from a source.

Drilling Fluid Formation Pressure

(Fluid) Barrier:

The hydrostatic head of the wellbore fluid is greater than the formation pressure.

AP

SSR

UPR

MPR

LPR

DrillingBOP



Primary well barrier:This is the first object that


Secondary well barrier:

This is the second object that


Well Barriers Drilling, Coring, Tripping



Formation Pressure

BOP

RamsTubulars

Casing

Safety Valves

Choke/Kill line valves

Cement

Wellhead

SOME OF THE (ELEMENTS) THAT FORM THE BARRIER ENVELOPE



BOP

Rams

Safety Valves

Casing

Choke/Kill line valves

Wellhead

Cement

Tubulars

SOME OF THE (ELEMENTS) THAT FORM THE BARRIER ENVELOPE



Barrier Components and Associated Equipment

• A barrier may need several components to be considered a barrier.

• A BOP has multiple components and associated equipment such as controlsystems, hydraulic power supply etc.

• A BOP is therefore considered a single barrier.

• A single point failure (of the wellhead/BOP connection) will negate the

barrier.

• Associated equipment such as control systems, hydraulic power supply

needed to activate the barrier should be considered ‘safety critical elements’

as much as the BOP.



Well Barrier Acceptance Criteria.

• Well barrier acceptance criteria aretechnical and operational requirements that

need to be fulfilled in order to qualify thewell barrier or WBE for its intended use.



Acceptance Criteria

Function and number of well barriersThe function of the well barrier and WBE shall be clearly defined.

• One well barrier in place during all well activities and operations,

including suspended or abandoned wells, where a pressure

differential exists that may cause uncontrolled cross flow in the

wellbore between formation zones.

• Two well barriers available during all well activities and operations,

including suspended or abandoned wells, where a pressuredifferential exists that may cause uncontrolled outflow from the

borehole/well to the external environment.



T bl A R ti l k t ti f d i lli BOP d ll t l i t



Table A. Routine leak testing of dri lling BOP and well control equipment

Before Drilling out

Casing

Periodic

Surface

Deeper

Casing &Liners

Weekly

Each

14Days

Each 6Months

WP Working Pressure

MWDP Maximum Well Design Pressure

Maximum Section Design Pressure

Function Testing shall be done from alternating

panels/pods

Tubing String Test Pressure

Or Maximum 70% of WP

Or at initial installation

From above if restricted by BOP arrangement

MSDP

Function

TSTP

1)

2)

3)

Function

Function

Function

Function

MSDP 1)

MSDP

MSDP 3)

MSDP

WP x 0.7

WP

WP

WP

WP

MSDP

MSDP

Function

WP

WP

WP

WP

WP

WP

WP

MSDP

MSDP

MSDP

MSDP

MSDP

Before

Well

Testing

Function

Function

Function

Function

MSDP

MSDP 1)

MSDP

MSDP

MSDP 3)

TSTP 1)

TSTP

TSTP

TSTP

TSTP

TSTP

TSTP

Function

MSDP

MSDP

Function

TSTP

TSTP

MSDP

MSDP

Function

MSDP

MSDP

MSDP

MSDP

MSDP

NOTE 1 All tests shall be 1,5 MPa (200 psi) to 2 MPa (300 psi) for 5 min and

high pressure for 10 min.

NOTE 2 If the drilling BOP is disconnected/re-connected or moved between

wells without having been disconnected from its control system, the initial leak

test of the BOP components can be omitted. The wellhead connector shall be

leak tested.

NOTE 3 The BOP with associated valves and other pressure control equipment

on the facility shall be subjected to a complete overhaul and shall be recertified

every five years. The complete overhaul shall be documented.

Frequency

Element

Stump

Annulars

Pipe Rams

Shear Rams

Failsafe Valves

Wellhead Connector Wedge Locks

MWDP 1)

MWDP

MWDP

MWDP

MWDPFunction

MWDP

MWDP

Function

WP 2)

MWDP 2)

MWDP 2)

MWDP 2)

MWDP 2)

Choke/Kill Lines

Manifold

Valves

Remote Chokes

Kill Pump

Inside BOP

Stabbing Valves

Upper Kelly Valve

Lower Kelly Valve

BOP

Choke/Kill line

and Manifo ld

Other Equipment

Legend



Table B - Failure of dril ling BOP and control systems

Barrier

element/equipment Actions to be taken when failure to test

Annular Repair immediately.

If WBE, repair immediately.

If WBE, repair immediately if no other pipe rams is available for that pipe size.

Rams that failed to test to be repaired at a convenient time.

If both valves in series have failed, repair immediately. If one valve in series has failed,

repair after having set casing.

If one has failed, repair immediately.

If both have failed, repair immediately. If one has failed, repair at a convenient time.

Same as for shear ram.

If one or more have failed, repair after having set casing if size is covered by another

ram. If not, repair immediately.

Immediately: Stop operation and temporary abandon well. After having set casing:Carry on with the operation and repair after having set the next casing.

Convenient time: Applicable for WBE’s that are not required.

Shear ram

Pipe ram (upper, middle, lower)

Choke valves, inner/outer

Kill valves, inner/outer

Marine riser choke and kill line *

Yellow and blue pod *

Acoustic – shear ram *

Acoustic – pipe rams *

*Floating Installations

Nomenclature :



Pressure direction

• The pressure should be applied in the flow direction.If this is impractical, the pressure can be applied againstthe flow direction, providing that the WBE is constructed

to seal in both flow directions or by reducing thepressure on the downstream side of the well barrier tothe lowest practical pressure (inflow test).



Documentation of leak and function testing of well barriers

All well integrity tests shall be documented and acceptedby an authorized person. This authorized person can be

the driller, tool-pusher, drilling and well intervention

supervisor or the equipment and service provider'srepresentative.

The chart and the test documentation should contain

• Type of test,• Test pressure,

• Test fluid,

• System or components tested,

• Estimated volume of system pressurized,• Volume pumped



‘Swiss Cheese Model’

• What Is Human Error?

Human error is an imbalance between what the situation requires, what the

person intends, and what he/she actually does.

• Human error happens when people:

Plan to do the right thing but with the wrong outcome (e.g., misdial a correcttelephone number; give the correct instruction but to the wrong person)

Do the wrong thing for the situation (e.g. turn an alarm off)

Fail to do anything when action is required (e.g. fail to report faulty

equipment)



• Why do Errors Happen?

As imperfect humans, we have inherent limitations in our abilities. We will

make mistakes. To answer the question of “why do errors happen?” or “whydid the error happen?” it is necessary to look beyond the person who madethe error.

Simply put, errors happen when multiple factors come together to allow

them to happen. What we usually call “human error” is really “system error”.People are one part of a system that includes all of the other parts of theorganization or work environment – equipment, technology, environment,organization, training, policies, and procedures. Human error is rooted infailure of the system or the organization to prevent the error from

happening, and if an error happens, failure to prevent the error frombecoming a problem.





Examples of defenses:

• Checking drilling mud weights.

• Challenging response procedures (being told to do something youknow is wrong).

• Setting alarms correctly.

• Following correct testing procedures.

• It is when these defenses are weakened and breached that humanerrors can result in incidents or accidents.

• These defenses can be portrayed diagrammatically, as severalslices of Swiss cheese (and hence the model has become knownas Professor Reason’s “ Swiss cheese” model)

Swiss Cheese Model

The concept of ‘defenses’ against human error




• Some failures are ‘latent’, meaning that they have been made atsome point in the past and lay dormant.

• This may be introduced at the time a well barrier was designed ormay be associated with management decisions and policies.

• Errors made by front line personnel, such as Supervisors, Drillersetc, are ‘active’ failures.

• The more holes in a system’s defenses, the more likely it is that

errors result in incidents or accidents.

• In certain circumstances, when all holes ‘line up’, blowouts occur.



Simple ‘Swiss Cheese Model’ explaining how a blowout could happen

Active failure: Fluid barrier breached when pulling pipe too fast

reduced hydrostatic pressure and allowed the well to flow.

Latent failure: Inadequate mud checks failed to pick up on reduced mud weight?

Reservoir

Hydrocarbons

Latent & Active failures: Delayed detection. Well monitoring not

done resulting in increased kick size. Annular Fails to seal.

Latent & Active Failures. Secondary barrier element breached due

to incorrect procedures (Tool joint across pipe rams).

Shear rams fail to shear pipe causing escape of hydrocarbons and explosion on rig floor.



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