### Efektywna pojemność komór magazynowych gazu w pokładowych złożach soli kamiennej

#### Abstract

Effective capacity of gas storage caverns in stratiform rock salt deposits

A b s t r a c t. Potential locations of underground natural gas storages in Poland are the Zechstein stratiform salt deposits in the Łeba Elevation and the Fore-Sudetic Monocline areas as well as salt domes placed in the central Poland. Preliminary analysis indicates that the storage caverns may be effectively located in the salt deposits with: a homogeneous layer of salt at least 150 m thick and with top surface placed at depths smaller than 1800 m (Ślizowski et al., 2006). Such conditions are complied by 4 locations in the Łeba Elevation and 9 locations in the Fore-Sudetic Monocline. Capacity of storage cavern depends on its volume and the range of storage pressure. Also important is temperature of the deposit because of its influence on the amount of stored gas and convergence rate change (loss of cavern volume in time). The following estimation assumes, that due to leaching factors, equivalent diameter of the caverns does not exceed 60 m and their height is 50 m smaller than the deposit thickness (thickness limit for roof pillar, floor pillar and cavern neck — Guarascio, 1998). The minimum and maximum storage pressures are increasing linearly along with a depth of cavern (OElizowski et al., 2007, 2009). The cavern convergence was estimated using a formula in which: dV

A b s t r a c t. Potential locations of underground natural gas storages in Poland are the Zechstein stratiform salt deposits in the Łeba Elevation and the Fore-Sudetic Monocline areas as well as salt domes placed in the central Poland. Preliminary analysis indicates that the storage caverns may be effectively located in the salt deposits with: a homogeneous layer of salt at least 150 m thick and with top surface placed at depths smaller than 1800 m (Ślizowski et al., 2006). Such conditions are complied by 4 locations in the Łeba Elevation and 9 locations in the Fore-Sudetic Monocline. Capacity of storage cavern depends on its volume and the range of storage pressure. Also important is temperature of the deposit because of its influence on the amount of stored gas and convergence rate change (loss of cavern volume in time). The following estimation assumes, that due to leaching factors, equivalent diameter of the caverns does not exceed 60 m and their height is 50 m smaller than the deposit thickness (thickness limit for roof pillar, floor pillar and cavern neck — Guarascio, 1998). The minimum and maximum storage pressures are increasing linearly along with a depth of cavern (OElizowski et al., 2007, 2009). The cavern convergence was estimated using a formula in which: dV

_{konw }/dt = A×e^{-(Q/RT)}(p_{g}- p_{z})^{n}, where: (dV_{konw }/dt)—relative convergence rate; p_{g}—gas pressure; p_{z}—rock massif pressure at the depth of cavern center; T—temperature; A, Q, R, n—constant coefficients. The formula parameters were calculated on the basis of parametric study, where the cavern convergence at different depths was analyzed using a numerical model based on finite element method. The convergence rate depending on the pressure difference between gas pressure and the primary rock massif pressure for different temperatures is shown in Figure 1. Storage cavern capacities calculated considering the above assumptions (initial capacities and after 15 years, which is a half of the planned operation period) in selected areas are presented in Table 1. Values of primary storage capacities obtained for caverns placed in the Fore-Sudetic Monocline appeared higher than those for caverns from the Łeba Elevation, mainly because of large thickness of salt deposits. However, after 15 years the capacities tend to equalize because the convergence rate of the caverns placed in the Łeba Elevation is smaller, due to a lower primary temperature of the rock massif.