DESIGN SPECIFICS OF HARD ROCK CAVERNS FOR HYDROCARBON STORAGE, FIFTY
YEARS OF FEEDBACKS AND RECENT DEVELOPMENTS
*Thierry You, Sophie Laurent, Nicolas Gatelier
Géostock France
2, rue des Martinets
92569 Rueil Malmaison Cedex - France
(*Corresponding author: thierry.you@geostock.fr)
DESIGN SPECIFICS OF HARD-ROCK CAVERNS FOR HYDROCARBON STORAGE; FIFTY
YEARS OF FEEDBACK AND RECENT DEVELOPMENTS
ABSTRACT
Hard-rock caverns for hydrocarbon storage are a very particular type of underground facility
controlled not only by local administrative and regulatory constraints that can be very specific, but also by
the possible risks of geotechnical or geomechanical failure. Each such facility throughout the world is a
prototype that needs to be adapted to very different site conditions. The straight forward application of
design methodologies from relatively similar fields (mines, tunnels) can be very useful, but risks holding
back the scientific and technical improvements needed by an engineering industry in full development.
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Primary characteristic is that the facility is designed to be stable and gas tight for a long but likely finite
period, in other words the abandonment of the future voids for future generation is a real concern which
becomes more and more important worldwide to the new designers. Lessons have been learned with the
first underground storages recently safely closed after long decades of good economic success. The post
mining lessons and statistics are much useful for long term stability studies but comparisons easily
plead for storage underground facilities.
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Second characteristic, consideration has also to be given to the fact that storage caverns have also to be
stable and gas tight, which involves further operational constraints, plus to the fact that product
movements will induce variations in pressure and temperature. Such variations generally have
permanent, as well as possible transitory, effects on the rock mass and its water circulation. Some
useful rules have been imparted to operators over the last decades in order to limit the chances of
unwanted transitory effects, such as excessive gradient-induced forces that can be harmful for gas
tightness when pressure rises, as well as for block stability when pressure drops.
Possible induced mechanical disorders go from tension cracks opening to large blocks and roof beams
instabilities. New numerical tools can now help the designer to quantify these risks. The concern
generally ends up with design cares and operational constraints.
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Third but not least in this presentation is major block potential instabilities. Large cavern are excavated
in several phases and a huge block (“mega-wedge”) can become unstable only after the last blast. A
methodology based upon the findings and structural mapping performed during accesses, top headings,
smaller galleries excavation and BHTV analysis can be successfully used to anticipate the location and
geometry of these blocks and analyze their stability Attention to design, along with follow-up
observations during early excavation phases, 3D structural mapping and dedicated tools should be used
to validate the cavern support and progressively bring about the needed adaptations during construction
when switching from a mainly empirical ‘rock classification based’ support design to a deterministic
‘site stability analysis and observational’ design.
We present the bases of innovative and new design methodologies as used today by Geostock to address
these risks on projects in France, North America and Asia.
Figure 1 –Potential room and pillar caving
Figure 2 – Displacement analysis of a block subject to coupled flow forces
KEYWORDS
Underground, storage, lessons, abandonment, transient, flow, force, block, wedge, risk, design, methodology