Proposed Requirements for Calculating Emergency Planning Zones for Sour Wells, Sour Pipelines and Sour Production Facilities

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Proposed Requirements for Calculating 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

Provincial Advisory 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 Response
  Requirements 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 EPZ
  to protect public SAFETY (protect against
  fatalities or serious irreversible health
  effects)
• Replaces the simple release rate based equations
  (or nomographs)
• EPZ derived from new requirements remains first
  step. Actual size and shape of the final EPZ must
  reflect 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
  EPZ includes mitigation actions NO EUB
  PRE-APPROVAL
• Applicable to new applications, ERP updates AND
  interventions

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Proposed Requirements
Base Case MANDATORY

• REQUIREMENTS
• (Minimum Standards)
• Sour Gas Release Rates
• Gas composition
• Depressurization (REAL GAS EFFECTS)
• Release Duration
• Dispersion Modelling
• Meteorological Conditions
• Concentration Fluctuations
• EPZ Endpoints

EUBMODELS (Screening Level EPZ Calculation) Techni
cal Descriptions and Formulations User Guide
Tutorial Software Package
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Release Rates

• For wells maximum release rates required as
  described in Guide 56
• For pipelines mass release rate profile from a
  guillotine break must be calculated using the
  maximum 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 they expand
  and cool
• Well releases are sensitive to wellhead exit
  conditions (pressure, temperature, hole diameter)
• More detailed calculation may result in buoyant
  release
• 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 the
  duration of the sour gas release are permissible
  (documented and PRACTICAL)
• For pipelines ignition not allowed as a
  countermeasure
• releases not typically long enough for manual
  ignition
• 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
  acceptable because a sour gas release from a well
  or pipeline occurs 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 as the calculation using a complex terrain
  model for comparison purposes

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Complex Terrain Criterion - H2S Releases

• Requirements now address issues of terrain
• Buoyant releases may require complex terrain
  modelling
• Compare terrain elevations in EPZ to terrain
  criteria defined in EUBMODELS
• Criteria based on EUB Guide 60 (Flaring)
• kinetic energy lift sufficient to overcome
  temperature gradient

complex
criterion
parallel
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Toxic Load End Points

• Endpoint described by toxic load criterion
• LKCnt
• same adverse effect for low concentration over
  longer 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 provide conservatism
  to protect public safety (i.e. if level achieved
  would not expect fatality or other serious
  irreversible adverse effect)

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EPZ Calculation Process
EUBMODELS Base Case (Mandatory)
EPZ pre-approval from EUB not required
EPZ to be used for Public Involvement
EPZ tuned to reflect site specific features
Acceptable
EUBMODELS BC Parameters varied
EUB assessment
ERP
Acceptable
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 practical
  mitigation measures used
• Operational implications (e.g. ESD valve trip
  points)

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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 with stakeholders
  depending on impact compared to previous methods
• Revise Guide 71 targeting fall 2004
• EUBRISK and EUBHVP EUBMODELS can be adapted
  possibly undertake in new fiscal year

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EUBMODELS Structure
Runs 54 times for met matrix
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Summary of PROPOSED Requirements

• Requirements in draft Requirements in Guide 71
  still apply
• No reduced EPZ application (size of EPZ
  determined by varying parameters) - single EPZ
  can be taken forward to communities for
  discussion and fine tuning
• EUB review post public involvement as part of ERP
  assessment REALISTIC MITIGATION
• Requirements applicable to new applications, ERP
  updates 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

draft.protocol_at_gov.ab.ca