BOP Basic Safety Functions

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BOP Basic Safety Functions

Katrine Harsem Lund

Principal Engineer, Department Manager

Scandpower AS

2011.10.11





Deepwater Horizon



Agenda

• What is a BOP/BOP Stack

• Safety Functions for a BOP Stack and Safety Integrity Levels (SIL)

• Critical components in BOP control systems and their reliability



What is a BOP?

• A blowout preventer

(BOP) is a large,

specialized valve used to

seal, and control oil and gas

wells.

• A BOP Stack (Well control

package) is the assembly of

well-control equipment

including preventers,

spools, valves, and nipples

connected to the top of the

wellhead.

• Topside/Subsea BOP stacks

Fig: A typical BOP Stack

Drill pipeAnnulus



A BOP Stack consists of multiple components…

• According to NORSOK D-001 "Drilling Facilities", paragraph 5.10.3, a BOP shall as a

minimum consist of the following:

– One (1) annular preventer

– One (1) shear ram preventer

– Two (2) pipe ram preventers – Minimum one (1) Choke Line outlet

– Minimum one (1) Kill Line outlet

– One (1) Wellhead coupling or connector

– Minimum two manual gate valves

– Minimum two remote operated gate valves.



BOP Stacks



Preventer valves

Annular Preventer Pipe Ram Shear Ram



How does a Ram valve work?



Safety functions of a BOP Stack

• Prevention of blowouts and well leaks

• OLF Guideline 070, defines the following functions for the BOP:

1. Seal around drill pipe

2. Seal an open hole

3. Shear drill pipe and seal off well.

• Thus the guideline differentiates between two main functionalities and set SIL levels

for:

• The annular preventer/pipe ram function (function 1)

• The shear ram function (function 2 & 3 combined).



No valves closed



Seal around Drill pipe



Shear drill pipe and seal off well



Setting A SIL Level for the BOP Safety Functions

• The BOP’s are used for a number of drilling related safety functions

– Well intervention

– Drilling

• A SIL level is only set for the drilling BOP

• Based on data from a Scandpower report “Blowout and Well Release Frequencies”, it

is estimated that the industry is operating with a “blowout prevention reliability”

somewhere close to SIL 3 on average.



Setting a SIL Level for the BOP Safety Functions

• The OLF- guideline discussion concludes with the following:

• “Setting a SIL 3 level to either function would lead to a significant increase in the

standard for drilling BOPs. The challenge lies mainly in the need for documentation of

the system reliability, Setting a SIL 3 level would most certainly also result in the need

for changing the existing control system. It would also be necessary to include

additional RAMs in standard BOP assemblies.”

• The required PFD/SIL for the BOP function for each specific well should be calculated

and a tolerable risk level set as part of the process applying for consent of exploration

and development of the wells. As a minim um the SIL for isolat ion u sing the

annulus fun ct ion sh ould be SIL 2 and the minimum SIL for closing th e

blind/shear RAM should be SIL 2.”



There are MANY components in the BOP control system!

• Shuttle valves

• Hydraulic Reservoir

• Filter

• Check valves

• Accumulator bottles

• Bleed valves

• Flow Totalisers

• Push-to-hold button

• Indicator lights

• Hydraulic pumps

• Pipe Ram valves

• Hydraulic Block valves

• Pressure gauges• Drillers Panel

• Pressure transmitter

• Wedge locks

• Gate valves

• Kill & Choke valves

• Shear Ram valve

• Flow transmitter

• Pilot valve

• Pneumatic Block valve

• Pressure regulator

• Hydraulic booster pump

• Pushbuttons

• SEM

• PCL

• Analogue input/output

• SCM

• Acoustic Transmitter

• Isolation valves

• Flow transmitter

• Solenoids

• Umbilical

• Tool pushers panel

• SPM valves

• Pressure Indicators

• Etc.

• Etc.



Components in BOP & control system

• How to decide which components are critical, and which are for information

only, or not critical? – FMECA with client, including operators/drillers

– SIL Workshops with client, including operators/drillers

– Accumulator bottles shall store hydraulic pressure to necessary volume and

pressure to enable closing-opening-closing operation of all rams +25% of volumefor one closing operation of each ram - function independent of many failures in

the hydraulic system



Build Reliability Block Diagrams

OLF Guideline 070 used to determine which functions of the BOP that

shall be SIL rated

Initiator(s) Logic

SIL 2 = 100 %

35 %

PFD < 0.0035

15 %

PFD < 0.0015

A BFinal

Element(s)

50 %

PFD < 0.0050



Reliability Block Diagram example topside BOP



Reliability Block Diagram example subsea BOP



Challenges

• All the SIFs for the BOP are manually initiated - Human Factors??

• Difficult to find relevant reliability data

– Generic data

– Data from vendors

• Redundancy?

• Not always possible to use pipe rams or shear the drill pipe!



Not possible to Shear/close pipe ram



Remaining issues/Questions

• When is it possible to move the drillpipe up/down if pipe ram/shearram cannot close?

• Everything is manually initiated - Impact of Human Factor?

• The testing of the Shear ram does not include actual cutting of thepipe. I.e the main function is not really tested – Test independentfailures

• Should other BOP functions have a SIL rating?

• Is all critical components identified and included in the SIL function?



Should other BOP functions have a SIL rating?



References

• OLF Guideline 070

• NORSOK D-001

• NORSOK D-010

• Sintef Memo: ”Barriers to prevent and Limit Pollutants to sea”

• Sintef Memo: ”Drill, not Spill”

• Transocean Deepwater Horizon Investigation report chp. 3.4

• BP Deepwater Horizon Investigation report

• Sintef Report ”Reliability of Subsea BOP systems for Deepwater

application, Phase IIDW”



For more information, please contact:

Katrine Harsem Lund

Principal Engineer, Department Manager at Kjeller Office

Scandpower AS

T +47 98 66 08 11

E [email protected]

W www.scandpower.com

w www.lr.org

BOP Basic Safety Functions

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