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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Underground storage Mined caverns technologies MINED CAVERN
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DISSUSED MINES
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Underground storage Mined caverns technologies Lavera LPG Storage Caverns
Lavera Butane Cavern – Construction OSR2G Nancy Fr2013
Operation Shaft Area 6
Construction of mined caverns Geostock Designer or owner’s assistant: UNDERGROUND STORAGE IN MINED CAVERN GEOSTOCK EXPERIENCE 6
25
5
CAVERNS CONSTRUCTION
20
4 15 3 10 2
5 1
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2011
2009
2007
2005
2003
2001
1999
1997
1995
1993
1991
1989
1987
1985
1983
1981
1979
1977
1975
1973
1971
1969
0
1967
0
CAVERNS COMPLETED (CUMULATIVE)
SITE UNDER CONSTRUCTION PROJECTS COMPLETED
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Mined caverns technologies and associated risks Principes
Operability
Stability
Hydraulic Containment
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UNDERGROUND STORAGE MINED CAVERNS TECHNOLOGIES
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 OSR2G Nancy Fr2013
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UNDERGROUND STORAGE MINED CAVERNS TECHNOLOGIES Product containment Criteria
ground level
water table water gallery
water curtain
flow-lines
maj 11/01
unlined caverns
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Operation shafts
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Various lay-out adapted to geological conditions
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UNDERGROUND STORAGE MINED CAVERNS TECHNOLOGIES Diesel Oil Storage of May–sur-Orne
Upper Levels – (Morts terrains)
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Access Shaft (Fontenay-le-Marmion)
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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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UNDERGROUND STORAGE MINED CAVERNS CONSTRUCTION METHODOLOGY Pyongtaek LPG Cavern
U-1 Crude Oil Cavern
30m
18m
17.5m
22m
12.8m
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UNDERGROUND STORAGE DESIGN METHODOLOGY
A mined storage cavern is neither A mine A civil work
A laboratory
But our design team learns from all and from all projects
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Methodology & Codes why?
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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Underground storage Mined caverns GEOGAZ - LAVERA Propane and Butane Storage Caverns Layout
GEOGAZ - Propane GEOGAZ - Butane
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SIMPLIFIED DESIGN CHART FOR ROCK ENGINEERING ( BIENIAWSKY - 1987 ) OSR2G Nancy Fr2013
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Typical mode of failure, rock falls
J. Fine 1993 OSR2G Nancy Fr2013
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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
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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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Mined Caverns SYDNEY (Australia)
Owner: ELGAS 83 000 m3 Propane
Main features:
Parallel galleries - Sandstone Length: 910 m - Section 142 m3 Depth: 124 m Beginning of construction: 1996 Commissioning: 2000
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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
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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
Design adaptation High horizontal stress consideration Joint opening model
900 elliptic - crown
800
Sv = 48 bar
ovaloid - crown
haunch
rectangle - haunch
700
crown
3.5 Sv
elliptic - sidewall
Tangential stress (bar)
sidewall
H
600
Main Geotechnical features:
ovaloid - sidewall rectangle - sidewall
500
W
400 300 200 100 0 -100 -200 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
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Feedbacks 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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Specificity of large caverns(2) Need of a fine tuned structural investigation in order to adapt bolt support: MUW-10
MUW-6
MUA2 W
MUB1 W
MUB2 W
V.6.287
V.10.215
MUA1 W
MUW-8
Section V9 Ch.242.6
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GEOTECHNICAL RISKS Geological Mapping: … collection and interpretations
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Mined Caverns GARGENVILLE (near Paris - France)
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+
Owner: GEOVEXIN 130 000 m3 Propane
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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LPG underground storage Operation shaft dewatering vent
LPG outlet LPG inlet
gas LPG liquid LPG water clay concrete fail safe valve CAVERN
Maj 08/98
instrumentation
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LPG pumps
water pumps
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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 Weathering
1 of rock walls 2
Ageing of supports
3
Seismic shaking
A Collapse of Cavern or Accesses
Possible exclusion under certain conditions (INERIS DRS-09-103911-09771A) Local or general collapse
Increase of interstitial 4 pressure and gradients Zone poorly supplied with natural water
11 Local increase of permeability on walls
D Local drop of hydraulic gradient and confinement.
C Cavern pressure exceeding critical pressure for leak
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Loss of hydrodynamic containment of the cavern 43
Séquence 2 : Risk assessment (2/2)
J. PIRAUD – Incertitudes et risques géotechniques - 29/01/13
Vraisemblance
Matrice des risques 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
Conséquences
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.
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Conclusions 2 Discover the truth through practice and again through practice verify and develop the truth- Mao Tse Toung Nature to be commanded must be obeyed- Francis Bacon
Complexity of geotechnical risks encourage us toward the virtue of humility and listening. 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 Awareness and vigilance naturally lead to design validation and monitoring. Feedbacks and Design Validation Loops remain essential. ”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.
