Geological and hydrogeological features of the lower Permian carbonate locally bituminous complex of the Tatarstan

Abstract

© 2020 IOP Publishing Ltd. All rights reserved. The Lower Permian bituminous complex is characterized by complex hydrogeological conditions. The predominant type of reservoir is mixed porous-fractured-cavernous. Water layers lateral prevalence is directly related to the degree of fracturing and cavernous of dolomites and limestones. Regional hydrogeological studies have shown that at the dividing ranges the Lower Perm sedimentary stratum is anhydrous, and in the river valleys it is water-rich. The center parts of such areas are erosive incisions of river valleys. From the periphery to karst regions center, a consistent increase in well flow rates and a decrease in piezometric groundwater levels from the slopes of dividing ranges to the river valleys are observed. In the domed sections of the South Tatar Arch in the Asselian - Sakmarian sediments, calcium-sulphate waters with a total salinity of 1.5 to 3.5-4.0 g/dm3 are prevalent. Sodium sulfate waters appear within the western slope of the arch. Within the eastern part of the Melekess Depression, the Asselian-Sakmarian stage groundwater deposits are already completely sulphate-sodium. The predominance of sodium components over calcium in groundwater is observed during total salinity of 4.5-5.5 g/dm3. In the areas of the Melekess Depression, where the Lower Permian sediments are drowning, groundwater acquires to sodium-chloride composition.