Teréga: more than 50 years’ experience and operations in gas storage

We operate two underground natural gas storage facilities, at our Lussagnet (Landes) and Izaute (Gers) sites. Already containing around a quarter of France’s gas storage capacity, their geographical position means they have a major role to play at the crossroads of south European gas exchanges.

The Europe-wide opening up of markets and the multiplication of exchanges has led us to pursue their development in response to the constant growth in storage. A number of projects have been undertaken to modernise the infrastructures and increase their capacity.

The commissioning of the Izaute site in the Gers department (32) in 1981 was closely linked to the increasing demand for gas and the increasing volume of exchanges, particularly within Europe. It is linked to Lussagnet by two pipelines 600 mm in diameter and approximately 10 km long. The location favours centralised coordination from Lussagnet.

Today, the Izaute site lays claim to a total authorised storage volume of 3 GNm³, a total developed storage volume of 3 GNm³, 10 injection/draw-off wells and 15 inspection wells.

The maximum draw-off flow from our two sites is 48 MNm³/day.

40 million years ago, Lussagnet and Izaute were on the coast, at the mouth of a river. This area received all the deposits deriving from erosion of the Massif Central, and particularly sandy deposits. It was that erosion which formed the different geological strata which now form the subsoil of our two sites.

This sandy layer encloses a groundwater deposit – an aquifer – which extends below the whole of southwestern France, from the Pyrenees to the north of the Bordeaux region, and across to the foothills of the Massif Central. And after 40 million years of sedimentation, that layer is now surmounted by a blanket of clay approximately 500 metres deep and forming a perfect seal. In the meantime, the compression which raised up the Pyrenees also created folds in the subsoil, and particularly the structures at Lussagnet and Izaute, which form an inverted bowl shape.

The two storage sites are managed and controlled from the Lussagnet site. The resulting centralisation of all the gas processing and compression facilities on that site enables better coordination of the management of the two storage facilities. It also contributes to improved performance and competitiveness.

The surface installations chiefly comprise:

• Pipelines enabling the gas to be directed to the various processing and compression installations;

• processing installations dedicated to the drawn-off gas (the injected gas does not require prior processing);

• compression units for the draw-off and injection phases.

We have established a monitoring network comprising numerous wells to inspect the aquifer at our gas storage sites. The aim is to track any changes in the depth of the groundwater and the physical-chemical characteristics of the water. 

This monitoring network enables us to make sure that our operations are coordinated with others using the groundwater:

• The Adour-Garonne water agency;

• the drinking water distribution industry;

• farmers;

• spas.

Twice a year, we engage two independent laboratories to carry out a water quality inspection. In addition, all these tests are forwarded to the authorities.