THREE TYPES OF STORAGE

Storing natural gas underground is the simplest, safest and most discreet solution. The sites chosen are naturally waterproof, and gas is stored at great depth. The types of reservoirs chosen depend on the geological structure available.

Storage in depleted fields: nature developed

When their geological characteristics and location allow it, depleted natural gas or oil fiels may be converted into underground storage sites. This in effect involves re-injecting the natural gas into a geological structure which has already stored hydrocarbons over several million years. The shafts are adapted to their new function and a central plant manages all the facilities.

Storage in aquifers : nature replicated

Aquifere storage sites occupy geological stuctures similar to those of natural fields. They are used by injecting gas under pressure at great depth into the rock under pressure. The gas progressively replaces the water without changing the underground architecture. A true natural reservoir, the domeshaped rocky structure is crowned with a waterproof cover of rocks which ensure the gas is kept underground.

Storage in Salt caverns : natural recycled

These storage sites comprise a series of caverns sunk into the waterproof and non-porous rock salt layer. They are remarkably watertight. The caverns are created by injecting water which dissolves some of the extracted water in the form of brine.

There is then room for natural gas, which is injected and stored in gassy form at hight pressure. Between one and three years are required to excavate a cavern with a final volume of anything from 100,000 to 1 million m3.