ABSTRACT
The Mechelinki Salt Deposits are situated at the northern termination of the Polish Zechstein Basin near the Baltic Sea coast (Fig. 1). In lithostratigraphic terms, the MSD correspond to the Oldest Halite salt bed (first Zechstein cycle-PZ1). This salt bed is underlain and overlain by anhydrite beds-the Lower and Upper Anhydrite, respectively. Above the Upper Anhydrite, a sulphate-carbonate-clay succession occurs, identified as second (PZ2) and third (PZ3) Zechstein cycle deposits. Borehole data indicate that Permian deposits accumulated on Silurian basement and they are covered by a sequence of Triassic, Lower-to-Middle Jurassic, Upper Cretaceous as well as Cenozoic deposits (Fig. 2). The top of the Oldest Halite rock salt bed occurs at depths ranging from 946 m to 996 m below sea level at present. The thickness of the rock salt bed varies between 123 and 286 m. Despite thickness changes, the salt bed is regarded as horizontally layered, depicting both primary
1 INTRODUCTION
Horizontally layered rock salt deposits are commonly regarded as non-deformed rock formations, suitable for studies on primary sedimentary features as well as for location of underground storages. This paper presents results of investigations on internal structure and vertical variability in geo mechanical parameters in rock salt deposits targeted for gas cavern construction. The investigations were carried out in Zechstein salts in northern Poland in the area of Kosakowo Underground Gas Storage (Kosakowo UGS) within the Mechelinki Salt Deposits (MSD), where a gas storage is constructed by Investgas S.A. for Polish Oil & Gas Company (PGNiG S.A.). The studies included analyses of meso-and micro-scale structures in core samples and subgrain size palaeopiezometry in halite. Independently uniaxial and triaxial compression and creep tests were performed. Integration and interpretation of these geological and laboratory test data is the scope of this paper.
