Propose Dep z Requirements Eub March 162004

8/13/2019 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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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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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

[email protected]

Documents

Propose Dep z Requirements Eub March 162004