It has already become noticeably cooler, rainy days are becoming more frequent, and natural gas consumption is starting to rise steadily. After all, gas is not only used for cooking, but also for heating. And for generating electricity. In order to meet demand in the winter months, the natural gas has to be kept “in storage”. Nature has done an amazing job here and created two types of stores. Here to explain what they are and how gas is stored hundreds of meters below the earth and then withdrawn again is Erich Holzer.
Gas consumption is tied to many factors. The weather, the temperature, the time of day, but also the time of year. While in summer a relatively low amount of natural gas is used, the demand in winter rises sharply and can be up to six times higher. A large percentage of European households heat their homes with natural gas. In Austria around one in four households heats with gas, in Germany even one in two. Natural gas is the most popular heating system for the German homes. However, the majority of countries are unable to completely meet demand through domestically produced gas and so natural gas has to be imported via pipelines. “Natural gas is produced throughout the whole in year in broadly regular amounts and transported from the natural gas field to the end customer. That means that in the summer months there is a surplus supply of natural gas, which then balances out the higher demand in the winter months”, explains Erich Holzer, Managing Director OMV Gas Storage GmbH. But this requires that it first be stored. And for this storage we draw on the geological features of Mother Nature: pore storage and caverns.
Today older gas reservoirs can be used for gas storage. Where nature safely stored gas for millions of years, today we can use it again for storage. After all, Mother Nature is the best builder.
Erich Holzer, Managing Director OMV Gas Storage GmbH
A sturdy sponge: Pore storage
Depleted gas reservoirs are ideal natural storage solutions. Natural gas is stored in the pores of the stone at depths of up to 1,200 m and at different levels, known as horizons. “There is a popular misconception that producing natural gas leaves hollow spaces underground. On the contrary, natural gas is found in porous rock, like a stone sponge. Natural gas stores refill the porous rock with what was inside it more than 300 million years ago”, explains Erich Holzer. A closed layer of rock seals the store upwards. Pore storage is primarily used for long-term storage of gas reserves – mostly for seasonal demand. You can see the scale of the pore storage and how it works in the following video using Schönkirchen (Austria) as an example – OMV’s largest store.
Salt out, natural gas in: Storage in salt caverns
For some idea of the scale, the Eiffel Tower fits into a single one of these caverns. And yet in North-German Etzel there are a full 73 salt caverns next to each other – with average heights of around 300 meters and widths of around 60 meters. At present 4.5 bn cubic meters of gas and over 10 mn cubic meters of crude oil are stored here. “Enormous hollow spaces are formed during the extraction of salt, as in the salt dome of Etzel and in contrast to the pore storage. Water is fed into the layers of the salt dome via drilling and in this way the salt that is released is finally pumped to the surface and then processed. After two to three years this results in ‘tanks’, which are ideal for storage due to their natural resistance to leakage”, explains Erich Holzer. These storage caverns can take in natural gas faster than pore storage, making them suitable for short-term deployment, for example when balancing out peak demand throughout the course of a day.
Division of labor: Cushion gas and working gas
The optimal withdrawal and replenishment of natural gas requires a specific pressure inside the storage. “The requisite minimum pressure in the store is maintained by so-called ‘cushion gas’, which remains permanently in the cavern or the pore storage to guarantee stability. In contrast, the ‘working gas’ is the gas stored by the customer, which can be withdrawn or replenished at any time”, says Erich Holzer. So, let winter come – thanks to the pore storage and salt caverns, there’s no need for anyone to shiver even during the coldest seasons.
Fact box: Storage
- Demand for natural gas in Europe is around 500 bn m³
- The most important natural gas suppliers for Europe are Norway and Russia
- OMV stores almost three bn m³ natural gas
- Austria: 2.2 bn m3 in pore storages
- Germany: 475 mn m³ in caverns
- OMV and its infrastructure meets the demand of more than a quarter of Austria’s annual gas consumption; this corresponds to supplying around two mn households with natural gas for a whole year.