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Geohazard Assessments as Part of Risk Management for

Underground Natural Gas Storage

Presented to Southern Gas Association

By

James L. Gooding, Ph.D., PG

Geoclime, LLC

July 15, 2019

Making the Climate of Quality Work for Your Enterprise ©

Geohazard Assessments for Underground Natural Gas Storage

Information Review

July 15, 2019Presented to Southern Gas Association

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Geohazards Affecting Underground Natural Gas Storage (UNGS)

Regulatory Perspectives

Geohazard Assessment Process

Case History: Location-Specific Assessment

Geoclime Services



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Geohazards Affecting Underground Natural Gas Storage

(UNGS)


Definition of UNGS Geohazard


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A geohazard for underground gas storage is any natural force or event that can compromise mechanical or functional integrity of the reservoir (or cavern), wells or well control.


UNGS Geohazards: Surface and Sub-Surface


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UNGS Surface Geohazards: Severe Weather


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UNGS Sub-Surface Geohazards: Earth Movement


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Regulatory Perspectives


Regulatory Perspectives on Geohazards


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Prior to the Aliso Canyon, California, gas leak (2015-2016), geohazards were not formally addressed in regulations

PHMSA Interim Final Rule (IFR) for UNGS safety (as directed by the PIPES Act of 2016) — effective Jan 2018 —adopted geohazard assessments by reference to:

• API RP 1170 (Salt Caverns)

• API RP 1171 (Depleted Reservoirs and Aquifers)

Root-cause analysis (May 2019) of Aliso Canyon Well SS-25 implicated groundwater in casing

corrosion that led to gas leak.




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Reservoir Type

Geohazard Description per Adopted Standard

Standard Adopted in PHMSA IFR

(2016)

“Shall” or “Should” Statement*

Salt Cavern

“Elements of uncertainty that pose particular risks in salt include but are not limited to the edge of salt, shear zones, faults, high impurity zones, K-Mg salts, weak zones, zones with high creep potential, dissolution or collapse zones, nearby wells or other subsurface activities.”

API RP 1170;

Section 5.3.4.2

(Geologic Uncertainty)

“Additional buffer should be assessed on a site by site basis by a qualified geologist to account for uncertainty in locating the exact edge of salt and to allow for the possibility that salt quality with regard to geomechanical strength properties and impurity content tends to degrade towards the edge of salt.”

* Quoted from Standard but with emphasis added on “shall” and “should” as they occur.




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Reservoir Type

Geohazard Description per Adopted Standard

Standard Adopted in PHMSA IFR

(2016)

“Shall” or “Should” Statement*

Depleted Oil / Gas Reservoir or Aquifer

“Outside force ‒ natural causes

Weather related and ground movement

• Heavy rains, floods, lightning, earth movements, groundwater table changes, subsidence, etc. that could result in:

• damage to facilities/impact to service reliability.”

API RP 1171;

Section 8.4.2

(Threat and Hazard Identification and Analysis ― Methodology)

“The operator shall evaluate the potential threats and hazards impacting storage wells and reservoirs.”

“The operator should estimate risk from potential events that could occur related to potential threats and hazards to individual facilities, such as wells, and by region when considering the reservoir.”

“The operator should perform periodic evaluations of hazards, threats, and risks related to potential events in order to account for changes in perception of likelihood or consequence in event potential.”

* Quoted from Standard but with emphasis added on “shall” and “should” as they occur.




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Main takeaways from PHMSA IFR (2016)

Geohazard assessment is part of risk management — which is a shall requirement in effect as of 2018

The limited references to geohazards are:

• Broadly defined, with a few examples, in API RP 1171

• Focused on “Salt creep or collapse” in API RP 1170

• Implied [49 CFR 192.12] that all geohazards are to be considered for all reservoir/aquifer and salt-cavern UNGS

• NOTE: PHMSA audits include “risk management” even though only API RP 1171 explicitly includes risk-management plans

• UNGS Operator is responsible for identification and assessment of facility-specific geohazards



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Geohazard Assessment Process


Geohazard Assessment with Time-Dependent Changes


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Geohazard Assessment as Annualized Risk Priorities


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Geohazard Assessment in Three Stages


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Case History: Location-Specific Assessment


Geohazard Assessment Case Study


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“Cornhusker Gas Storage” (hypothetical UNGS facility in Nebraska)

Logan County

41.505° N, 100.429° W

Exercise the assessment process (one surface and one sub-surface geohazard)

Flood (or Flash Flood)

Earthquake

Illustrate the assessment results


Geohazard Assessment Case Study


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“Cornhusker”

U.S. UNGS Facilities


Geohazard Assessment Case Study: Flood Risks


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River, stream or potential flood channel




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Area affected by historical flood events




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5 Miles

South Loup River

Wild Horse Creek

“Cornhusker”




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Damaging Heavy-Rain & Floods

“Cornhusker” area has experienced multiple drought-flood cycles

Records show damaging events during 2009-2012

Most recent trend (2019) possibly into another “flood” cycle

Annualized flood risk estimated from 1996-2018 records

NL = 9% ± 16% (long term)

NL = 29% ± 5% (flood cycle)

NC = $50K damage / eventData Sources:

NOAA SPC Storm Events Database

NOAA NCEI Precipitation Timeseries

New Flood Cycle?




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“Cornhusker” area is vulnerable to floods from South Loup River Stream-gauge data not

available before 2017

At least one flood-stage event in early 2019

Flash flood warnings depend upon weather radar

NEXRAD KLNX (North Platte NE), 32-mile range

Annualized flood risk estimated from 1996-2018 records ND = 12–24 hr (Flood - gauge)

ND = 1–2 hr (Flash Flood - radar)

Data Sources:

USGS 06781900 South Loup River at Pressey WMA (northeast of Oconto).

USGS National Water Information System


Geohazard Assessment Case Study: Seismic Risks


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Potential ground acceleration (PGA; %g) over 50 yr (USGS 2014)




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Potential ground acceleration (PGA; %g) over 50 yr (USGS 2014)

Potential for ground-shaking damage (%) over 1 yr (USGS 2018)

Only 1-Yr Model for Central &

East is displayed




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“Cornhusker”

Seismic Activity

PGA (% g) in 50 yr (USGS 2014)

Ground-shaking damage

(% likelihood) in 1 yr (USGS 2018)

Earthquake epicenter (2000-2018)

100 Miles

2

4

4

6

1 - 2

2 - 3

8 - 10




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PGA (% g) in 50 yr (USGS 2014)

Ground-shaking damage (% likelihood) in 1 yr (USGS 2018)

Earthquake epicenter (2000-2018), within 100 miles

Depth (feet) to Pre-Cambrian (NGS)

50 Miles

4,000

3,500

3,500

6,000

2,500

3,500




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“Cornhusker” earthquakes probably originate within p€bedrock

Depth to pre-Cambrian bedrock is 1.1 – 1.2 km (3,500 – 4,000 ft)

Earthquake focal depths are 1.2 – 15 km

Not correlated with known faults (i.e., none mapped)

2018 “Swarm” was at same depth range as 2000-2017 background

1.2 – 15 km

Cluster at 5 km

Data Sources:

USGS National Earthquake Catalog




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Data Sources:


“Cornhusker” earthquake magnitudes most often M ≤ 3.5

Most frequent model magnitude is M ≈ 3.0

Model short tail predicts other earthquakes of M < 2

Model long tail suggests very few earthquakes of M > 4.5

Reference Information

M = 2 (felt by people)

M = 4 ‒ 5 (scattered, minor damage)

M ≥ 6 (significant damage)




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“Cornhusker” area is subject to weak earthquakes

Steady background of M = 2-3 events since 2000

Spike in activity in 2018, including one M = 4.1

Not correlated with known faults (i.e., none mapped)

Annualized earthquake risk estimated from 2000-2018 records

NL (M ≥ 2) = 53% ± 9%

NL (M ≥ 4) = 5% ± 8%

NL (Damage, USGS) = 2% ± 1%

NC = $500 (FEMA-USGS Hazus, 2017)

ND = 0 hr (no earthquake warning)

Data Sources:


Date

RangeEvents

2000 -

201714

2018 27

Total 41


Geohazard Assessment Case Study: Risk Priorities


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Calculate risk priorities Risk Priority Number (RPN)

RPN = AL • AC • AD

L, C and D converted from decimal estimates (N) to integers (A; look-up table)

RPN for “Cornhusker” flood risk NL = 9% AL = 1

NC = $50K AC = 2

ND = 1 hr AD = 4

RPN = 1 • 2 • 4 = 8

RPN for “Cornhusker” earthquake risk NL = 2% AL = 1

NC = $0.5 K AC = 1

ND = 0 hr AD = 5

RPN = 1 • 1 • 5 = 5

Annualized

Index of

Importance

(A)

Likelihood

(Probability of

at Least One

Event per

Year)

Consequence

(Damage per

event)

Detectability

(Warning Time

before Impact

of Event)

5 ≥ 90% ≥ $500 K < 1 hr

4 70 – 89% $300 - $499 K 1 - 12 hr

3 50 – 69% $100 - $299 K 13 – 24 hr

2 30 – 49% $10 - $99 K 25 – 36 hr

1 1 – 29% < $10 K > 36 hr

IMPORTANT NOTE: This table is illustrative only. Its

actual content will depend upon detailed attributes of

individual facilities and their risk tolerances.

This assessment indicates that mitigation against flood risk (RPN = 8) should be a higher priority than mitigation against earthquake risk (RPN = 5).


Geohazard Assessment: Summary


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Assessment of geohazards at UNGS facilities is required by PHMSA as part of risk management.

A complete geohazard assessment should include the following checklists:

Initial assessments can be done as desktop studies; site visits later.

Assessment results should include risk priority numbers (RPNs).

• Surface Geohazards (Severe Weather)

• Flood or flash flood• Tornado or strong winds• Hail• Lightning• Ice / snow storm• Tropical cyclone• Wildfire

• Sub-Surface Geohazards

(Earth movement)

• Earthquake• Natural• Human-induced

• Landslide• Subsidence

• Aquifer• Karst• Mine / other

• Mass movement• Soil expansion / contraction• Salt creep


Geoclime Services


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Geoclime provides quality and risk management consulting for organizations involved in energy, water, science and engineering. We help our clients with geotechnical pursuits to achieve and document compliance with operational regulations, contracted quality requirements and process integrity:

We are a small enterprise that specializes in support for businesses where outsourced services must add clear value and be affordable. No project is too small when a client asks for our help.

Geoclime is chartered as a limited liability company (LLC) in the State of Texas, United States of America, and is licensed by the Texas Board of Professional Geoscientists (Geoscience Firm #50225).

Geoclime, LLC Telephone: +1 281-451-8375P.O. Box 13 Website: https://www.geoclime.com1600 Main Street E-mail: [email protected], Texas 77586 USA

• Geohazard assessments

• Root-cause analyses• Risk management plans

• Process audits

• Gap analyses• Management plans & procedures

https://www.geoclime.com/downloads

mailto:[email protected]



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Question & Answer Session

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