The influence of lithofacies features of the Permian natural bitumen-saturated reservoir rocks on groundwater formation conditions

Abstract

The reservoirs rocks of natural bitumen deposits of the Lower Permian system and the Kazanian stage of the Tatarstan territory are considered. The relationship of groundwater composition in bitumen reservoirs with lithologic features of water-saturated rocks is shown. Rocks compositions contribute to formation of three water classes in oil deposits: hydrocarbonate, sulfate and chloride. Hydrocarbonate waters lie over erosion downcutting of rivers in the most elevated territory part. Their origin is associated with hydrolysis and carbon-dioxide leaching of the Permian terrigenous rocks. Inland waters of hydrocarbonate-sodium (soda) composition of bitumen deposits are located above local drainage basis. They are formed as a result of sulfate reduction processes in deposits. The inland waters of sulfate composition of calcium and sodium groups are characteristic of deposits located below the drainage basis. Their origin is associated with dissolution of gypsum and anhydrites, as well as with ion exchange reactions between the calcium of the solution and the sodium which absorbed by rock complex. Chloride waters associated within the eastern side of the Melekess Depression, where there is an active hydrodynamic relationship between the Permian system aquifers and chloride-calcium salt brines of the Carboniferous rocks. The nature of the distribution and presence of aquifers in deposits is determined by the lithological features of reservoir formation.