Oil deposits of the Visean stage of the northeastern part of the Tatarstan Republic

Abstract

The sections of wells that have discovered oil-bearing deposits of the Bobrikian horizon, within the Aktanysh-Chishminsky trough in the northeast of the Tatarstan, are considered. In the terrigenous complex of the Bobrikian age, alternation of mudstones, siltstones, and sandstones is observed. According to the peculiarities of composition and porosity, mudstones and siltstones are classified as impermeable rocks, sandstone - as reservoir rocks. The study of sandy reservoirs showed that the rocks are characterized by a monomineral quartz composition, uniform oil saturation, fine-grained structure, massive texture. The porosity of sandstones is 15-20%. The pores are connected and form winding channels up to 0.1 mm in diameter. Sandstones form covers over the biogenic structures of the Tournaisian Stage, wedging out laterally and being replaced by dense siltstones. Good capacitive properties of the rock were acquired due to the leaching of calcite cement during the migration of water-oil fluids. Currently, sandstones contain oils with a predominance of light oil and medium paraffin fractions.