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TIGF storage

Teréga operates two underground natural gas storage facilities, at our Lussagnet (Landes – 40) and Izaute (Gers – 32) sites. They help supply natural gas to the transport and distribution grids in the far southwest, as well as part of Spain and the rest of France. In 2015, these two structures accounted for roughly 24% of French underground natural gas Storage Capacity.

The Lussagnet storage site began operating in 1957, at the same time as the Lacq gas field (Pyrénées-Atlantiques – 64) came on stream. It was intended at that time to regulate the production of natural gas from the Lacq plant.

The Izaute storage site, located roughly 10 km from the Lussagnet site, was brought into service in the early 1980s to keep up with the increasing demand for natural gas.

The role of underground natural gas storage sites in France

The underground storage sites enable us to meet a number of needs:

  • to deal with seasonal variations in natural gas demand and cover peaks in consumption. Whilst the main supply flows are relatively constant throughout the year, the needs of French consumers vary considerably with the seasons. Monthly consumption in the winter can be almost five times as high as in the summer months;

Seasonal variations in gas consumption compared with constant supply

Seasonal variations in gas consumption compared with constant supply

  • to ensure security of the country’s supply;
  • to provide a balancing tool for management of gas flows across transport networks.

The operating principles of Teréga’s storage sites


The Lussagnet and Izaute underground storage sites each have a porous, permeable geological stratum, approximately 500 to 700 metres below the surface, which is the “reservoir” rock.

That layer, which is several metres thick, is shaped into a dome, overlaid by an impermeable “overburden” rock. Mainly made up of clays, it means the gas can be trapped and ensures the storage does not leak.

General principles of Lussagnet and Izaute underground storage

General principles of Lussagnet and Izaute underground storage

The injection phase

During periods of low consumption (summer), gas from the Transport Grid is injected through operating wells into the porous, permeable “reservoir” rock. It accumulates there through the effect of gravity, locally displacing the water contained in the rock’s pores.
For this to happen, the gas pressure must be higher than the water pressure. This condition is met thanks to compression units located at the surface.

The draw-off phase

During periods of high consumption (winter), the gas is drawn off through the operating wells. It is then distributed across the Transport Grid to top up supplies and meet the increased demand.

This draw-off operation results in a drop in the gas pressure in the “reservoir” rock. The surrounding water then returns to its initial place in the pores in the rock.

The operating wells

The operating wells enable the surface installations to be connected to the underground geographical layer in which the gas is stored, also known as the “reservoir” rock.

They allow gas injection and draw-off operations to take place.

They are arranged in clusters: areas prepared to accommodate several wells, the associated pipework, and the equipment needed for drilling machinery.

Surface installations

The surface installations principally comprise:

  • a network of gas pipelines enabling the wells to be connected to the treatment and compression installations;
  • treatment installations dedicated to drawn-off gas (the injected gas needs no prior treatment);
  • gas compression units for the draw-off and injection phases.

The treatment and compression installations are located at the Lussagnet centre and controlled from the control room.

Treatment units for drawn-off gas.

Treatment units for drawn-off gas.

Before re-joining the Transport Grid, the drawn-off gas is subjected to three processes within the treatment installations, in order to meet the currently applicable commercial standards.

  • Dehydration, which consists of removing the water which has saturated the gas while it has been in storage.
  • Desulphurisation, which enables traces of hydrogen sulphide (H2S) found in the stored gas to be removed.
  • Odorisation through the addition of THT (Tetrahydrothiophene). This operation is performed for safety reasons; it means users can detect gas by its smell.

After treatment, the drawn-off gas is pressurised to a sufficient pressure for distribution through the Transport Grid.

At the end of the injection phase, the gas from the Transport Grid is compressed to a sufficient pressure.

Underground natural gas storage – Operating principles

Underground natural gas storage – Operating principles

Storage monitoring

In addition to the operating wells, other wells are drilled specifically to monitor the “reservoir” rock, the “overburden” rock and the aquifer. They enable full-time checking of:

  • the pressure of the stored gas;
  • the extent of the gas store;
  • the leak-tightness and integrity of the “overburden” rock;
  • the physical and chemical characteristics of the water in contact with the gas.

Main characteristics of Teréga’s storage sites

Technical characteristics of the two sites
Lussagnet Izaute
Date of commissioning 1957 1981
Total authorised storage volume (GNm³) 3.5 3.0
Total volume of storage in operation at 01/01/2014 (GNm3) 2.8 3.0
Number of injection/draw-off wells15 10
 Number of inspection wells  14  15
Maximum draw-off rate ≈ 45 MNm3/d while half of the usable volume remains in storage
Installed compression ≈ 30 MW

Storage: Teréga’s investments

Over recent years, a number of projects to secure and modernise the storage infrastructures and increase their capacity have been completed.

Development plan

 Teréga is implementing a plan to expand its storage capacities, aiming to:

  • supporting the development of the Transport Grid and flows passing through the France-Spain interface;
  • increasing fluidity in the European gas market;
  • enabling customers to secure their continuity of supply in a sometimes unpredictable geopolitical context;
  • anticipating the development of combined cycle gas-fired power stations (CCCG);
  • offering new commercial storage deals to suit new market needs.

Stockages souterrains : performance et intégrité

Dans le but de garantir une gestion rigoureuse et maîtrisée des ressources naturelles, Teréga mène d’importants travaux de recherche pour développer une connaissance approfondie
des structures géologiques et des aquifères de stockage. Ces travaux font appel à des disciplines diverses des sciences de la terre (géologie, géophysique, hydrogéologie et

L’objectif est notamment :

  • de mettre en évidence la dégradation naturelle de composés traces présents dans le gaz naturel, par les bactéries présentes dans le sous-sol ;
  • de garantir une sécurité optimale et une étanchéité parfaite des stockages en mesurant les effets saisonniers engendrés par l’injection et le soutirage de gaz.

Par ailleurs le gaz naturel étant amené à verdir via la production et le stockage de biométhane, ou via des solutions de Power to Gas avec production d’hydrogène et de
méthane de synthèse, il est nécessaire d'en étudier les impacts potentiels dans les stockages dans les différentes composantes du sous-sol (aqueuses, minérales ou microbiologiques).
Une teneur limite acceptable en hydrogène et biométhane dans le gaz naturel injecté est ainsi définie.

Safety and modernisation plan

An infrastructure safety and modernisation plan was implemented alongside that development plan. Since 2007, this has given rise to various construction projects, including:

  • the construction of a new HQE (High environmental quality) building: intended to accommodate the offices and control room, it is built on the edge of the site to guarantee a high level of protection for staff;
  • the replacement of an older well by drilling new ones with double safety barriers and incorporating the latest technologies; 

  • the installation of a new firefighting network at the Lussagnet site, and a new emergency decompression system;
  • the replacement of the old compressors by two new, more energy-efficient ones.

These different projects help guarantee that customers can enjoy:

  • a high level of storage installation availability;
  • a high quality of service.

Map of installations

Map of installations

List of Teréga territories operating in the 15 departments of the South West

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