OIL CAVERNS Risk mitigation through awareness and vigilance

Thierry YOU

OSR2G Nancy Fr 2013

Geotechnical Risk Mitigation for Hydrocarbon Storage

Panorama of Hydrocarbon Storage

Design Methodology

Feedbacks

Conclusions

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Geotechnical Risks

Reference list

- Manuel de Mécanique des roches Tome III

- EC7 Eurocode 7

- NF94-500 Geotechnical Tasks

- ISRM WG Design Methodology, Hudson & Feng

- ASCE Geotechnical Baseline Report

- AFTES GT1, GT25, GT32

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Géostock Expertise

Different types of hydrocarbon storage:

Salt leached caverns Mined cavern Aquifer, depleted field

Natural Gas, LPG, liquid hydrocarbons LPG, Liquid Hydrocarbons Natural Gas

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DISSUSED MINES MINED CAVERN

Underground storage Mined caverns technologies

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Lavera LPG Storage Caverns

Operation Shaft Area Lavera Butane Cavern – Construction

Underground storage Mined caverns technologies

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Construction of mined caverns

Geostock Designer or owner’s assistant:

UNDERGROUND STORAGE IN MINED CAVERN

GEOSTOCK EXPERIENCE

0

1

2

3

4

5

6

19

67

19

69

19

71

19

73

19

75

19

77

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79

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81

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87

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99

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01

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03

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05

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07

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09

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11

CA

VE

RN

S C

ON

ST

RU

CT

ION

0

5

10

15

20

25

CA

VE

RN

S C

OM

PL

ET

ED

(C

UM

UL

AT

IVE

)

SITE UNDER CONSTRUCTION

PROJECTS COMPLETED

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Operability

Stability

Hydraulic Containment

Mined caverns technologies and associated risks

OSR2G Nancy Fr2013

Principes

11

Caverns are unlined

Tightness only depends on natural

convergent flowrates from the

rockmass towards the cavern :

this is the hydrodynamic

containment principle

Containment principle = HYDRODYNAMIC PRINCIPLE

UNDERGROUND STORAGE MINED CAVERNS TECHNOLOGIES

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maj

11

/01

ground level

water table

water gallery water curtain

flow-lines

unlined caverns

UNDERGROUND STORAGE MINED CAVERNS TECHNOLOGIES

Product containment Criteria

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Operation shafts

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Various lay-out adapted to geological conditions

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Access Shaft (Fontenay-le-Marmion) Upper Levels – (Morts terrains)

UNDERGROUND STORAGE MINED CAVERNS TECHNOLOGIES

Diesel Oil Storage of May–sur-Orne

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Cavern dimensions: large variations

Volume :

from 8 000 m3 (LPG) to 2 Mm3 (Crude Oil)

Height:

from 6 m (chalk) to 32 m (granite / gneiss)

Section :

Up to 650 m²

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U-1 Crude Oil Cavern

18m

30m

12.8m

22m 17.5m

Pyongtaek LPG Cavern

CONSTRUCTION METHODOLOGY

UNDERGROUND STORAGE MINED CAVERNS

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A mined storage cavern is neither

A mine

A civil work

A laboratory

But our design team learns from all and from all projects

UNDERGROUND STORAGE DESIGN METHODOLOGY

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Methodology & Codes why?

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Rockbolting alternatives based on a individual judgement. (Drawing from a cartoon in a brochure on rockfalls published by the Department of Mines of Western Australia)

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GEOGAZ - LAVERA Propane and Butane Storage Caverns Layout

GEOGAZ - Butane

GEOGAZ - Propane

OSR2G Nancy Fr2013

Underground storage Mined caverns

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SIMPLIFIED DESIGN CHART FOR ROCK ENGINEERING ( BIENIAWSKY - 1987 )

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Typical mode of failure, rock falls

J. Fine 1993

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Flowchart of rock mechanics modeling and rock engineering design approaches (Feung and Hudson, 2004).

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Typical failure modes of large underground cavern group and its related tunnels

27

Specificities of large sections

Likelihood of toe/wall failure

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Conclusions 1

Methodological advance will bring us huge progresses but also brakes to new ideas.

We still have to learn!

Feedback loops and validations remain essential.

“No theory can be considered satisfactory until it has been adequately checked by actual observations”. Prof. Ralf B. Peck.

Designers and regulatory bodies tend to place increasingly reliance on analytical procedures of growing complexity and to discount judgement as a nonquantitive, undependable contributor to design Prof. Ralf B. Peck.

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Mined Caverns ULSAN (South Korea)

Owner: SK-GAS

310 000 m3 Propane - 240 000 m3 Butane

Main features: Parallel galleries

Andesite and metasedimentary sandstone

Depth: 119 m (propane) - 63 m (butane)

Propane: length 830 m - Section 308 m2

Butane: length 629 m - Section 342 m2

Beginning of construction: 1984

Commissioning: 1988

Main Geotechnical features: Fault crossing

Careful mapping

Rock fall and repair works

Scale effect on wedges

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Main Geotechnical features:

Highly anisotropic environment

High horizontal stresses

Roof falls

Grouting works

Smooth blasting and tolerance control

Difficult construction supervision and

contractual environment

Design ‘model’ difficulties

Post construction environment

Main features:

Parallel galleries - Sandstone

Length: 910 m - Section 142 m3

Depth: 124 m

Beginning of construction: 1996

Commissioning: 2000

Owner: ELGAS

83 000 m3 Propane

Mined Caverns SYDNEY (Australia)

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ROCK FALL EXPLANATIONS (20+)

A large number of explanations were put forward by the parties involved, many of them with ulterior motives: unsuitable section, inappropriate and damaging explosive, poor workmanship (drilling, bolting, etc.), untested rock bolts, too differed bolt grouting, poor site organisation, unsuitable numerical and structural models, underdesigned rockbolts, inappropriate bolting patterns, unsuitable excavation sequence, poor and inefficient quality control, lack of design methodology (EC7), lack of monitoring and inspection, unforeseen stress release, random vertical joints, lack of spot bolt decision on visible instabilities, inclined defects in sheet facies, too high water pressure imposed in the fissures, etc.

At that stage, none of the specified monitoring measures that had been prepared for design validation (geological joint mapping, convergence measurement, profile mapping, pull-out test, etc.), that certainly would have helped as new design basic data, had been implemented.

Maintaining roof integrity was crucial for stability, as was established latter

(You et al. Johannesburg ISRM2003)

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Mined Caverns VISAKHPATNAM (India)

Owner: SALPG

127 600 m3 Propane - Butane mixture

Main features: Parallel galleries + 1 central access tunnel

Depth: 162m/msl

Length: 342 m

Section: 338 m2

2 operation shafts

Construction: 2004-2007

Main Geotechnical features: Design adaptation

High horizontal stress consideration

Joint opening model

-200

-100

0

100

200

300

400

500

600

700

800

900

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1

Slenderness W/H

Ta

ng

en

tia

l s

tre

ss

(b

ar)

elliptic - crown

ovaloid - crown

rectangle - haunch

elliptic - sidewall

ovaloid - sidewall

rectangle - sidewall

3.5 Sv

Sv = 48 bar

W

H

haunch

sidewall

crown

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DURING SITE INVESTIGATION :

Supervision by design team during drilling and testing

==> RQD on fresh cores

==> representative sample selection

==> site adaptation of water test

DURING CONSTRUCTION :

GEO SURVEY sometime after each blast

==> cartography geo-geo-hydro+ geometry

==> rock quality «i.e. Q factor »

==> adaptative support

==> water monitoring

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Feedbacks

Specificity of large caverns(2)

Need of a fine tuned structural investigation in order to adapt bolt support:

V.1

0.2

15

V.6

.287

MUW-10 MUW-6 MUW-8

Section V9 Ch.242.6

MUB2 WMUB1 WMUA2 WMUA1 W

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GEOTECHNICAL RISKS

Geological Mapping: … collection and interpretations

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Mined Caverns GARGENVILLE (near Paris - France)

Owner: GEOVEXIN

130 000 m3 Propane Main features: Chalk

Galleries EW and NS

Length: 1400 m (EW) - 1300 m (NS)

Section: 49 m2

Depth: 132 m

Beginning of construction: 1972

Commissioning: 1977

Abandonment: 2008+

Main Geotechnical features: Post peak behavior

Construction tolerances

Importance of construction record and operation

monitoring

Adaptative design

Closure design for abandonment procedure

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dewatering

Maj

08

/98

water pumps

CAVERN

gas LPG liquid LPG water clay concrete fail safe valve

LPG outlet

LPG inlet

vent

instrumentation

LPG underground storage Operation shaft

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STEPS OF GEOTECHNICAL RISK MANAGEMENT ( From AFTES GT 32+..)

1) Risk identification:

Each project is a prototype, no universal approach available

2) Hierarchize, assess and evaluate the risk:

Danger of subjectivity, explain to share

3) Risk treatment ( risk matrix, risk register, event tree)

Share between parties, role of insurance ( GBR, GDR)

4) Monitor and control

Check actions, vigilance

5) Memorize and capitalise lessons learned ( feedbacks)

Difficult but needed.

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Project studies and phasing

Project Development

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Risk Tree prepared for one known mined cavern storage 1/2

Possible exclusion under certain conditions (INERIS DRS-09-103911-09771A)

Local or general collapse

Local drop of hydraulic gradient and confinement.

D

Loss of hydrodynamic containment of the cavern

C Cavern pressure

exceeding critical pressure for leak

Zone poorly supplied with natural water

Local increase of permeability

on walls

11

Ageing of supports

Increase of interstitial

pressure and gradients

Seismic shaking

Weathering of rock walls

Collapse of Cavern

or Accesses

A 1

2

3

4

Séquence 2 : Risk assessment (2/2)

J. PIRAUD – Incertitudes et risques géotechniques - 29/01/13

Exemple of risk matrix Colours represent the resulting level of risk for each event (green : acceptable without further action ; red unacceptable risk).

The level of risk related to an event may be deemed more or les acceptable depending of targets and priority of Owner.

Decision to take action against a risk is therefore a task devoted to Owners and Engineers.

Possible 4 8 12 16

Peu Probable 3 6 9 12

Très peu Probable 2 4 6 8

Improbable 1 2 3 4

Faibles Moyennes Fortes Très fortes

Matrice des risques

Vra

isem

bla

nce

Conséquences

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Conclusions 2

”If something is discovered that does not agree with the hypothesis, rejoice! You can then really learn something new. You are on your way to an understanding of the problem”. Ralf B. Peck.

Feedbacks and Design Validation Loops remain essential.

Awareness and vigilance naturally lead to design validation and monitoring.

We need to carry out a vast amount of observational work, but what we do should be done for a purpose and done well- R.B.Peck

Complexity of geotechnical risks encourage us toward the virtue of humility and listening.

Nature to be commanded must be obeyed- Francis Bacon

Discover the truth through practice and again through practice verify and develop the truth- Mao Tse Toung