bop basic safety functions
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BOP Basic Safety Functions
Katrine Harsem Lund
Principal Engineer, Department Manager
Scandpower AS
2011.10.11
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Deepwater Horizon
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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
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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
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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.
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BOP Stacks
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Preventer valves
Annular Preventer Pipe Ram Shear Ram
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How does a Ram valve work?
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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).
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No valves closed
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Seal around Drill pipe
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Shear drill pipe and seal off well
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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.
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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.”
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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.
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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
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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
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Reliability Block Diagram example topside BOP
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Reliability Block Diagram example subsea BOP
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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!
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Not possible to Shear/close pipe ram
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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?
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Should other BOP functions have a SIL rating?
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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”
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For more information, please contact:
Katrine Harsem Lund
Principal Engineer, Department Manager at Kjeller Office
Scandpower AS
T +47 98 66 08 11
W www.scandpower.com
w www.lr.org