Well Control Incident and Risk Assessment Experience Well Control Incident and Risk Assessment
Experience
AGA UGS Workshop - Reno, Sept 2005 The following presentation has been prepared by Enbridge
Gas Distribution Inc. (Enbridge) based on its records of
events which occurred in 1995. This presentation has
been prepared for informational use only by members of
the American Gas Associations Underground Storage
Committee and should not be copied or distributed to any
other party without Enbridges express written consent.
Enbridge makes no representations or warranties
whatsoever as to the accuracy or completeness of this
presentation and Enbridge expressly disclaims any liability
whatsoever as a result of any persons reliance upon
statements or information set out below. How it all started.
Initial workover planned to repair wellhead
May 10, 1995
RIH w/ Baker retrievable bridge plug on wireline
Bridge plug hanging up, repeatedly getting stuck
Bridge plug finally stuck at 195m, wireline company not
confident that they could remove with wireline
Decision made to set the plug and pull with cable tool rig
When bleeding down wireline lubricator plug was
leaking slightly, tool hand convinced plug was
properly set and would not move
Wellhead repair continued Packer Retrieval
June 2 1995
Rig in Cable tool drilling rig. Above master
valve have orbit valve, tool trap and lubricator.
Lubricator pressure tested with well pressure
Assured by tool hand that plug could not be
released by setting down retrieving tools on
plug. 5000 lbs force had to be jarred down on
plug for equalization.
Field pressure was 730psig, brine column
above plug had hydrostatic of 375 psig. Blow-out starts
June 2 1995 @ 08:20
Cable tool set down on bridge plug, upon tagging the
plug the plug immediately released and began traveling
upward. Note: jars had not been set prior to the plug
becoming unset.
Slugs of water and/or gas were forced to surface at high
velocity
Tool trap on lubricator ruptured as the pressure surge
hit the surface components
Began venting gas to atmosphere.
Could not close orbit valve or master valve due to cable
in the well.
Initial Response
June 2, 1995 starting at @09:00
Emergency Response procedures initiated
Residences notified and evacuated, power cut off to homes
Road closed except to emergency personnel
Provincial and municipal agencies notified
Installed diverter lines
Attempted to pump cement to bridge off the leak,
unsuccessful after pumping 3 tonnes into lubricator
Called in Kieffer Pressure Control Corp.
Press release issued that afternoon through Ontario
Provincial Police
Through night, fire departments put on alert,
thunderstorm during evening What to do next?
June 3
Took x-rays to determine where cable was
located
Began manufacturing clamp
Second press release
June 4
Installation of Sutherland Clamp
Flow only through diversion lines
Observation well pressure 765 psig Freeze Operations
June 5
Decision made to freeze the lubricator assembly
between Orbit valve and tool trap
On second attempt, successfully froze wellhead and
were able to remove the broken equipment and install
another valve to regain control Well Controlled
Start Recovery
June 6
Able to remove tool trap and install 8 valve to
achieve isolation
Road blocks removed and residents notified to
return
June 7 to 15
Pushed cable below the master valve and
broke down wellhead assembly
Fishing out cable and tools Media Coverage
Press releases were made through the Ontario
Provincial Police.
Had media attention in local newspaper The Aftermath
Estimated gas lost was 69 million cubic feet.
Gas was vented for approx. 80 hours
Investigation by Ministry of Natural Resources
Lubricator and tool trap not rated pressure vessels,
insufficient design for pressures
Issues with plug setting and pulling procedures
Some confusion as to why a retrievable plug was run
instead of a drillable
Should always have bleed / kill lines installed and at the
ready
Emergency response was handled appropriately and
competently ERP Learnings.
Had landowner do an end around
Found out some time later that one landowner entered
their property through a back lane after being stopped
on the main road by the police.
Had issues surrounding amount of information
given to police
Need to give out enough information so landowners
know what the situation is.
Initiation of ERP have more structure in our
ERP now as to when top initiate and who to call New Procedures
New plug setting procedures
Bridge plug, Hydromite (cement) and second bridge
plug
For deviated / directional wells; two retrievable plugs
These will all be retrieved / drilled out by cable tool rig
under pressure
BOP Installation
Use shear rams, blinds and annular bag
Lubricators and tool traps engineered and
pressure tested
Plug pulling procedures.ensure pressure from
above when pulling or drilling out plugs Cable Tool Rig BOPs Recent Initiatives
Renewed ERP, table tops and mocks
Reviewed and rewritten ERP, clarifying emergency levels
Only have Level 1 and Level 3 emergencies
Run all personnel through 2 table tops and one full mock ERP
annually
Safety Boss review of ERP
Need to review headcount procedures
Importance of reviewing phone numbers and contact information
Landowner notification
Road Block kits
War room upgrades maps, drawings, communications Identified need to perform a risk assessment on
some of our wells Risk Assessment Review and
Enbridge Experience What is Risk?
RISK
=
Frequency
X
Consequence What kind of assessment
would you like to do?
Hazard Assessment
Risk = Likelihood X Severity
A-B-C-D; 1-2-3-4
Semi-quantitative Risk Assessment
Risk = Frequency Expression X Consequence
Expression
Quantitative Risk Assessment
RISK = Frequency X Consequence
Increasing
Cost & Time Recent Enbridge Experience
Enbridge worked with consulting company to
perform a Quantified Risk Assessment
Needed something concrete to justify additional
expenditures
New Version of CSA Z341 will stipulate the use of risk
assessments
Looking at the risk posed by wells to landowners,
environment and workers
Looked at both normal operating conditions and
workovers Hazard Assessment Semi-Quantitative Assessments
Approximations are made
for Frequency or
Consequence assigned a
scaled number which can
be used to determine
relative risk
Quantitative assessments
for one parameter can be
made
Provides a means of
ranking risk items Pipeline Semi - Quantitative
Assessment
Enbridge Storages pipeline RA was semi-quantitative When to do a QRA?
QRA is done when
the consequences justify the expense
(pipeline installations)
legislation requires quantitative treatment
(offshore installations)
acceptable installation safety is in doubt
(public exposure to consequences) QRA Framework
System
Description
Identify
Hazards
Corp. risk
Acceptability
Guidelines
Quantify
Risk
Emergency
Response Plan
Design changes
Operating changes
Land use Zoning
Risk Control
Monitor / Audit
Safety
Are Risks
Acceptable?
Yes
No Define QRA Study
Step 1 - Consider Scope & depth of study
for expense and use, schedule and budget Enbridge Study Examined gas wells which were in close
proximity to dwellings Proximity of one well to compressor station Studying the behaviour of sales gas upon
release; plume modeling Means of applying general risk factor to all of
the wells rather than having to do full QRA on
all wells Study Definition & Scope Some other goals of QRA studies Justify additional investment in safety valves Screen employee & site risks Screen public risk have had landowners ask
about how much risk the wells pose to their
homes Assist with emergency planning, evacuation Describe the System, Hazards
Step 2 - Describe the System Relatively simple in storage system when only
investigating wellhead to reservoir Had done a pipeline risk assessment from compressor
station to wellhead previously Rather than looking at each well, investigated a best
case and worst case well to determine differences
Step 3 - Identify Hazards
Qualitative outlines
Design parameters
HAZOPs
Workshop meetings Identify Incidents
Step 4 - Identify all incidents - Loss of
Containment of sales gas
equipment failures & imperfections
external impacts (3
rd
party)
overpressure
exceeded design limits
Human error Select Incidents
Step 5 - Select incidents for detailed study
incidents to satisfy study objectives
incidents to