Underground natural gas storage is a strategic link in the gas supply chain. It enables large volumes to be stored at high pressure, meaning that a quantity of gas will always be available, regardless of consumption. The volumes and pressures used are not compatible with storage at the consumers’ premises. Underground storage is therefore essential in ensuring the continuity of the natural gas supply to the general public and industrial customers alike.

As a responsible industrial operator, TIGF has made safety an absolute priority and has set itself ambitious targets to ensure maximal security at all stages from the design to the operation of underground storage. Strict rules issued and rigorously enforced by the authorities mean that underground storage is one of the safest storage methods.

TIGF operates two underground storage sites – Lussagnet and Izaute – in naturally gas-tight rock strata. Gas is stored between 500 and 700 m down, in a porous rock containing water (aquifer) at a location where the rock strata form a “bell structure”. The reservoir rock is overlaid with a layer of impermeable rocks more than 500 metres thick. This sort of structure means that a large quantity of natural gas can be stored at sufficient pressure, in a leak-tight fashion.TIGF storage

The storage perimeter is marked out at surface level by a vertical projection above the deep storage reservoir. The two storage facilities operated by TIGF have a storage area of approximately twenty square kilometres.

• The Lussagnet storage area covers all or part of the four communes of Lussagnet, Cazères sur Adour, Le Vignau and Hontanx in the department of Landes, as well as the Houga commune in the department of Gers.

• The Izaute storage perimeter covers all or part of the communes of Caupenne d’Armagnac, Laujuzan, Magnan, Mormès and Perchède in the department of Gers

The safety perimeter is used to mark out an area in which drilling or water boring operations could have an effect on the storage operation and vice versa. It covers the storage area, the surface areas being 51 km² for Lussagnet and 119 km² for Izaute. Within these areas, any work going deeper than 350 m must receive prior authorisation from the Prefect. This measure helps prevent any damage to the gas storage during underground work.

Risk control starts with risk identification and evaluation work: from the design through to the operation of the installations.

• Risk identification and evaluation is part of the research into hazards. The installation hazard study provides a description of the different accident scenarios which could occur, whether caused internally or externally. It evaluates the possible consequences of any accident and explains suitable measures to reduce the probability of an accident its effects. In accordance with the regulations applicable to storage, TIGF updates its hazard studies at least every five years.

• TIGF implements monitoring of its equipment and installations, their maintenance and their monitoring. This allows it to guarantee that operating conditions are maintained and its installations modernised over time.

Actions to prevent and deal with accidents are organised through a safety management system (SGS) applied by the operator, TIGF. It is subject to regular inspection by the Regional Directorate of the Environment, Development and Housing (DREAL).

TIGF regularly tests its safety equipment and its emergency plans, in consultation with the authorities and emergency services. The operator has set out an internal operations plan (POI), the purpose of which is to define suitable organisation and means to control an accidents confined to the side. TIGF also takes part in exercises initiated by the authorities (PPI: special intervention plan). In fact, in the case of an accident extending outside the boundaries of the establishment, the Prefect takes charge of the emergency response operation, implementing the measures set out in the PPI.