Propose Dep z Requirements Eub March 162004
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Transcript of Propose Dep z Requirements Eub March 162004
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Proposed Requirements forCalculating Emergency Planning
Zones for Sour Wells, Sour
Pipelines and Sour Production
Facilities
Presented by:Gary Neilson BSc(Hons) P.Phys
Public Safety Implementation Team
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Presentation Outline
Background
Proposed new requirements
EPZ calculation process
Implications
Future work
EUBMODELS Structure
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Background
Project initiated to address issues heard
by Provincial Advisory Committee on
Public Safety and Sour Gas*
Proposed EPZ calculation requirements
based on assessing the hazard footprint of
a sour gas release using dispersion
modelling*ProvincialAdvisory Committee on Public Safety and Sour Gas Findings and
Recommendations Final Report December 2000
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Background
In the past, disagreement between
experts and public about model
choices and inputs that will lead to
accurate, useful and credible results
Difficult for EUB to make informed
decisions in the public interest without
full understanding of differences
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Background
Draft requirements published mid-December 2003 Early draft February 2002
Technical workshop & focus groups
Peer review/EUB testing of EUBMODELS
Requesting feedback on clarity of the requirements/additional requirements
the supporting EUBMODELS documentation and software
March 31, 2004 (extended)
Requirements will be included in future revision of
Guide 71 - Emergency Preparedness and ResponseRequirements for the Upstream Petroleum Industry
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Proposed Requirements
Address suite of PSSG Recommendations (17,18,19, 58 and 62)
Define the minimum standards to calculate an EPZto protect public SAFETY (protect against fatalities
or serious irreversible health effects)
Replaces the simple release rate based equations (ornomographs)
EPZ derived from new requirements remains first
step. Actual size and shape of the final EPZ mustreflect site-specific features of the area
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Proposed Requirements
EPZ more realistically calculated characterization of the release (representative gas analysis,
source conditions at exit calculated, real gas effects)
dispersion modelling,
consequence modelling to a toxic load based endpoint
(concentration AND exposure time important) Credit for PRACTICAL mitigation actions (e.g.limiting release duration through ignition)
No reduced EPZ as presently defined as single EPZincludes mitigation actionsNO EUB PRE-
APPROVAL Applicable to new applications, ERP updates ANDinterventions
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Proposed Requirements
EUBMODELS (Screening
Level EPZ Calculation)
Technical Descriptionsand Formulations
User Guide & Tutorial
Software Package
REQUIREMENTS
(Minimum Standards)
Sour Gas Release RatesGas composition
Depressurization (REAL GAS EFFECTS)
Release Duration
Dispersion Modelling
Meteorological ConditionsConcentration Fluctuations
EPZ Endpoints
Base CaseMANDATORY
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Release Rates
For wells maximum release rates required asdescribed in Guide 56
For pipelines mass release rate profile from a
guillotine break must be calculated using themaximum licenced pressure
account for the emergency shutdown valve (ESD)
trip set points
the distance between ESD valves mass of gas in adjacent pipeline segments that
escapes before the valves close
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Depressurization - why are real gas
effects important?
Ideal gas laws under predict EPZ
Real gases can form liquid aerosol as theyexpand and cool
Well releases are sensitive to wellhead exit
conditions (pressure, temperature, holediameter)
More detailed calculation may result in buoyantrelease
Pipelines usually dense due to pressures EUBMODELS Base Case always dense release -
CONSERVATIVE
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Release Duration
Duration defines exposure time Duration for wells must be realistic for the scenario
(drilling, servicing or producing) and other site-specific factors
Duration for pipelines determined by transient mass
release through a guillotine break Countermeasures such as ignition that limit theduration of the sour gas release are permissible(documented and PRACTICAL)
For pipelines ignition not allowed as acountermeasure
releases not typically long enough for manualignition
self-ignition not guaranteed
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Dispersion Modelling
Worst case Met conditions assumed Dispersion model used must account for
real gas effects
dense or buoyant releases
For dense plumes parallel airflow model is acceptablebecause a sour gas release from a well or pipelineoccurs at or near ground level
Plumes that rise complex terrain model may be required
EUBMODELS Base Case must still be included in the
documentation supporting an EPZ calculation as well asthe calculation using a complex terrain model forcomparison purposes
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criterion
complex
parallel
Requirements now address issues of terrain Buoyant releases may require complex terrain
modelling
Compare terrain elevations in EPZ to terrain criteriadefined in EUBMODELS
Criteria based on EUB Guide 60 (Flaring) kinetic energy lift sufficient to overcome temperature
gradient
Complex Terrain Criterion - H2S
Releases
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Toxic Load End Points
Endpoint described by toxic load criterion L=KCnt
same adverse effect for low concentration overlonger time as high concentration for short time
concentration weighted (n) K accounts for concentration fluctuations
(dispersion models only predict averages)
Objective of endpoint is to provideconservatism to protect public safety (i.e. iflevel achieved would not expect fatality orother serious irreversible adverse effect)
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EPZ Calculation Process
EPZ to be
used for Public
Involvement
EPZ tuned to reflect
site specific features
EUBMODELS Base
Case (Mandatory)EPZ pre-approval from
EUB not required
EUBMODELS BC
Parameters varied
Acceptable
Acceptable ERP
EUB
assessment
Alternate Methods
EUBMODELS BC must also be
modelled using alternate methods
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Implications
Anticipate zones will change More effort required than previous simplistic
approach
detailed documentation (explaining mitigation
actions, variation of base case parameters,alternate methods)
Responsibility on industry to ensure practicalmitigation measures used
Operational implications (e.g. ESD valve trippoints)
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Future Work
Toxic load endpoints need further discussion workshop on H2S toxicity
objective to assist EUB in selecting safety endpoint
Ignition timing lower limit needs to be defined workshop planned
Address stakeholder comments
Develop implementation strategy withstakeholders depending on impact compared to
previous methods
Revise Guide 71targeting fall 2004
EUBRISK and EUBHVPEUBMODELS canbe adapted possibly undertake in new fiscal year
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EUBMODELS Structure
ExcelUSER INPUT USER OUTPUT
EUBFlash EUBSlab
EUBMODELS
Sp read s h eet Sp read s h eet
Runs 54 times
for met matrix
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Summary of PROPOSEDRequirements
Requirements in draftRequirements in Guide 71still apply
No reduced EPZ application (size of EPZdetermined by varying parameters) - single EPZ canbe taken forward to communities for discussion and
fine tuning EUB review post public involvement as part of ERP
assessmentREALISTIC MITIGATION
Requirements applicable to new applications, ERPupdates or interventions
Provide clarity to assist in EUB decisions
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Project Website
www.eub.gov.ab.ca/BBS/new/Projects/sgr.htm