Underground Storage - Hydrogeology: Objectives, Methods, Applications - page 303

C HAPTER D5
Underground Storage
Underground storage is essentially tied to energy problems. It is used
for gas storage, to smooth the contrast between the regular restocking by
providers and the irregular use by consumers. Aside from daily peaks due
to cooking before mealtimes, consumption is, indeed, highly variable: high
in the winter due to heating needs and low in the summer. Another need is
the handling of nuclear waste. The hydrogeologic problems encountered
are different. For gas, the presence of water is absolutely necessary in order
to prevent leaks and enable pressurization. For nuclear waste on the other
hand, areas with no water circulation are sought out.
1 UNDERGROUND GAS STORAGE
Four types of storage are commonly used:
• gas can be stored in old exhausted gas reserves, and this is the most
commonly used method. A project is under way in Trois Fontaines
(Marne) where the reconversion of a natural gas deposit will allow a
storage of around 3 billion m 3 ;
• storage in salt cavities, where a cavity is created by injecting water into
a salt deposit and extracting the resulting brine. The Manosque deposit
(Alpes de Haute Provence), 150 m below ground, has a capacity of one
billion m 3 . Those in Tersanne (Drôme) and Etrez (Ain) have a capacity
of 1.4 billion m 3 ;
• storage in an aquifer, where gas is injected at a pressure greater than
the hydrostatic pressure, in a confi ned aquifer below an aquiclude,
and pushes the water compressing it out laterally. This recreates the
equivalent of a natural reserve. The exploitation constraints impose the
permanent maintenance of a volume of approximately half of the stored
volume (the padding). Part of the gas can then be replaced by nitrogen.
In France, the Chémery site (Loir-et-Cher), with a total volume of 6.8
billion m 3 , enables the useful storage of 3.5 billion m 3 . The boreholes