The role of underground gas storages (UGS) in Poland is presented in the paper in view of the present situation in Europe, accounting for the safety of gas supplies, and economics. The issues related to UGS in EU and Poland were outlined with special emphasis on storage in salt caverns. Presently, six underground gas storages are used in Poland. Five of them arc located in depleted natural gas reservoirs, and one was made in salt caverns (UGS Mogilno). The total capacity of all active UGSs has recently increased from 1 255 mln m(3) in 2000 to 1 651.6 mln m(3) in 2006 (increment by 31.6%). In the same period the maximum withdrawal rate from the storages grew from 22.6 mln m(3)/day to 34.1 mln m(3)/day (increment by 50.5%), and the considerable part of this rate growth is associated with the UGS Mogilno. Gas can be withdrawn from salt caverns at extremely high rates. For this reason such caverns are particularly suitable for peak shaving purposes. The analysis of the working gas capacity of active storages in the years 2000-2006 reveals that at the beginning they have had considerable reserves but since the period 2002/2003 these capacities have been used out nearly completely. The withdrawal rate reserves can be observed only in the case of the cavern UGS Mogilno; it should be remembered, however, that it is usually limited by the gas transport abilities. The UGS Mogilno is in construction since 1989. The first stage of construction, covering 10 storing caverns of total capacity ca. 585 mln m(3) of gas accompanied with surface facilities was finished in 2005. The UGS Mogilno works as a peak shaving storage, with withdrawal rate of 30 mln m(3)/day, that is twice as big as the total of the remaining gas storages in Poland. In the years 2000-2003 the working capacity of UGS kept on increasing, resulting in an increment from 200 mln m(3) in 2000 to 331.3 mln m(3) in 2003. In 2004 the active capacity decreased to a level of 319.6 mln m(3), to increase to 416.8 mln m(3) in 2005. Presently the working capacity of UGS Mogilno is 371.6 mln m(3) (lowering of capacity is caused by technical causes - convergence of salt in comparison to maximal pressures of caverns).The maximal withdrawal rate of the storage also considerably oscillated. In the years 2000-2003 it increased from 10 mln m(3)/day to 30.3 mln. m(3)/day (capacity of surface facilities). Bearing in mlnd the restrictions in gas transition system, the present nomlnal deliverability of gas from this storage was 16 mln m(3)/day. Underground gas storages play more and more important role in a number of countries in the energy safety projects and optimization of the cost of delivery of gas to the consumers. The functions performed by the modern underground gas storages also change. Apart from traditional functions, e.g.: strategic reserve in case of interrupted deliveries (especially in the strongly import-dependent countries, i.e. almost all EU countries) or peak periods (traditionally, in Spring and Summer gas is injected to the storages, and then it is withdrawn from October to March) there are new business-oriented approaches to UGS: balancing on daily basis, gas prices arbitrage, i.e. market optimization gas price oscillations, general optimization of the entire system functioning, including the "swap" transactions. These functions require a number of in-out operations each year which can be done in the cavity-type storages. The emphasis exerted by the EU on liberating the gas market and promoting competition necessitates commercial prices for natural gas storing. Such prices, as presented in the paper, depend on a number of factors: geologic, technical and economic. In the case of storages built in the depleted fields or aquifers, most of the capital cost goes to the gas cushion, wells, and surface facilities, whereas in the cavern-type storages the cost of leaching domlnates over the other costs. Cavern construction is more costly than depleted field conversions when measured on the basis of euros per thousand cubic meters of working gas capacity, but the ability to perform several withdrawal and injection cycles each year reduces the per-unit cost of each thousand cubic meter of gas injected and withdrawn. The results of calculations performed by the authors revealing that commercial gas storing in Poland may be competitive to the prices in other EU countries. This can be source of considerable income for the potential operator.
