Porous media (Aquifers, Depleted fields)
A porous and permeable geological formation (the reservoir) can be used to store gas provided it is:
- overlain by an impermeable stratum (the cover) to prevent any upward migration of the gas;
- structured so as to ensure lateral containment, for example in the form of an anticline;
- situated, finally, at such depth (between 500 and 2000 m) that the range of pressures attainable in the reservoir is compatible with that of the transport system.
The formation may be a depleted oil or gas field or an aquifer which has never held hydrocarbons.
When storing gas, it is compressed and injected in gaseous state into the reservoir: it pushes back the water initially occupying the pores in the rock. At recovery, the gas is drawn off under the effect of its own pressure and water can possibly take its place.
Gas is injected and withdrawn through a series of production wells similar to those used in gasfield production. Surface facilities comprise mainly compression, treatment and metering equipment.
During the operational phase, monitoring wells check the position of the gas interface and the gas tightness of the reservoir.
Products stored:
- Natural gas
- Compressed air
- CO2