Underground gas storage facilities are an important part of the natural gas system. Supplies of natural gas from producers fluctuate only slightly during the year, as long-distance pipelines are, for economic reasons, dimensioned to be used equally throughout the year. As natural gas is used mainly for heating, its consumption in winter is substantially higher than in summer.
Storage of gas underground in summer, when there is a surplus, for increased consumption in winter is the most practicable and cheapest solution to this disproportion. A gas company can also purchase from producers a greater amount of gas in the winter, but in all likelihood for a much higher price and only up to a certain amount depending on the transmission capacity of the long-distance pipelines.
Underground gas storage facilities can be divided up into two groups according their use.
Seasonal reservoirs – These are reservoirs that are filled during the summer and then used to supply gas to the network in the winter. These reservoirs have a large storage capacity, but a smaller daily output. These reservoirs are usually located in used up gas or oil deposits and, exceptionally, aquifers. In both cases, the facilities are located in underground porous layers of rock with sufficient permeability. In the former, these layers used to be filled with gas or oil; in the latter, they used to be filled with water.
Spike reservoirs – These reservoirs cover natural gas consumption in short intervals when it is necessary to supply a large amount of gas into the network over a short period of time. As opposed to seasonal reservoirs, they can be filled up again during the winter to maximum capacity. In the world, these reservoirs are most often built in salt caverns, which form when water leaches out a part of the salt deposit.