French gas-storage project nearing completion. (Geomethane project)

Geomethane, jointly formed by Gaz de France and Geostock, is currently converting 7 of 36 solution-mined salt cavities at Manosque in southeast France from liquid hydrocarbon storage to natural-gas storage.

The facility, used for liquid hydrocarbons since 1967, is operated by Geostock subsidiary Geosel. The conversions are part of wider development (Fig. 1).

The seven cavities lie 900-1,500 m below ground and will operate over a pressure range of 6-18 MPa (60-180 bar). Aggregate storage will be 450 million normal cu m (MM cu m). The seven cavities are being commissioned over the period 1993-96.

In view of the large diameter (13 3/8 in.) of the original production wells and safety requirements, a unique high-capacity well completion has been developed for this project.

It will have two fail-safe valves and a flow crossover 30 m below ground to isolate the production well in the event of problems at the surface.

The project lies in the wooded Luberon Nature Reserve and due consideration has been given to locating the surface plant and blending it with the surroundings. The production wellheads are extra-low designs, the main plant was located outside the sensitive area, and the pipeline routes were landscaped.

20 years' development

Since the first prototype of natural-gas storage in cavities mined in salt was completed in the U.S. in 1961, more than 30 sites have been developed worldwide, representing more than 200 individual cavities.

If all gaseous, liquid, and liquefied gas products are included, this total becomes more than 1,000 cavities.

Gaz de France began its salt storage at Tersanne in 1968, followed in 1977 by Etrez, which is still expanding. It now has 30 cavities in all representing 1 billion standard cu m (bscm) of active natural-gas storage capacity.

This is modest compared with the 17 bscm capacity in Gaz de France's aquifer storage, but salt-cavity storage offers a much higher peak delivery rate.

In 1967, Geostock (subsidiary of the BP France, Elf France, Societe des Petroles Shell, and C.R.D. Total France) decided to develop liquid hydrocarbon storage in solution-mined salt cavities at Manosque.[1]

Gaz de France's growing demand for storage capacity in southeast France combined with availability of some of the Manosque cavities resulted more than 20 years later in the setting-up in 1989 of Geomethane.

Gaz de France also built 70 km of 750 mm (30 in.) gas pipeline from Manosque to Cabries (between Marseilles and Aix) to link with the national bulk-transport system.[2]

The Geosel cavities were built and operated under regulations governing underground storage of liquefied and liquid hydrocarbons embodied in Decree of Jan. 13, 1985, as amended by Decree No. 85-450 of Apr. 25, 1985.

Underground storage of combustible gas is subject to specific regulations set out in Decree of Nov. 6, 1962, as amended by Law of July 12, 1983, and Decree No. 88-220 (Mar. 8, 1988).

Geomethane's application procedure for a permit to store combustible gas was as follows:

* Application accompanied by environmental impact-assessment and risk report: submitted June 1990.

* Public enquiry: March 1991.

Two other enquiries, concerning the listed installations for the Gaude station and Cabries-Manosque pipeline were conducted at the same time by the same commission in order to submit the complete project to the public.

* Local scrutiny by county government and local communities: April-September 1991. …