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Storage engineering

From the gas reservoir to the underground gas storage

Austria has geological structures that are unique in Europe and ideal for gas storage. Gas can be injected into depleted reservoirs where gas accumulated  naturally over millions of years, at depths of over  1,000 metres. These former gas fields originated  over 20 million years ago, when organic matter in the primeval ocean that occupied today’s Prealps was  trapped by sandstone sediments. Over time the gas  migrated into the pores of the sandstone, forming gas reservoirs that can have an area of several square  kilometres. Layers of clay several hundred metres thick overlie the gas reservoirs, and this natural insulating layer makes the underground gas storage extremely safe. The proof of this comes from nature itself, since  the original gas reserves were held there for millions  of years.
RAG converts gas reservoirs into storage facilities when most of the gas has been extracted. Gas is fed into the reservoirs and withdrawn from them via wells when needed. Surface installations are also required. These include compressors to inject and withdraw the gas under pressure, and equipment to dry and clean it before sending it on its way to consumers. All these process units have been tried and tested over several decades, and are continuously improved. Our storage expertise makes a major contribution to gas supply  security in Austria and Central Europe as a whole.

Download illustration "Gas storage facility" (JPG)

How storage facility works

When gas arrives at a storage facility via a pipeline network it first enters a metering station where it is filtered, and the quantity and quality are measured. Injection and withdrawal take place via a number of wells. Where necessary, compressors (compressors with electric drive systems or gas driven turbocompressors) bring the incoming gas up to the right injection pressure. Since compression raises the temperature, the gas must then be cooled before being conveyed to the wellhead and injected into the natural rock formations. Care must be taken not to exceed the original reservoir pressure. The gas is withdrawn when it is needed, and processed for transportation. It must be dried as it will have absorbed moisture in the reservoir. Once it is on specification it enters the grid and is carried to the consumer.

Cushion gas

Cushion gas is needed to keep the number of wells and the scale of the surface equipment to a minitmum. Optimising the design of the storage facilities cuts operating costs, reduces the impact on the environment and minimises the disturbance in the vicinity of the surface installations. Some gas is always left in the reservoir as a "cushion", and only the working gas above it is injected and withdrawn.

The cushion gas is a major investment when constructing a storage facility, but pays off because it permits high gas withdrawal rates due to the constant base pressure in the reservoir.

Download illustration "How gas storage facility works" (PDF)


Thomas Plessnitzer
T +43 (0)50 724
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Tatjana Weilert
T +43 (0)50 724
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