Key words: the Cenomanian, Russkoye field, incised valleys, microscopic lamina, permeability, heterolyte filling, tidal flats, sand storms.
The major reserves of Russkoye field relate to the Cenomanian formations PK1-7 of pokurskaya suite that is characterized by a complex structure. That is determined by facies environment and uneven development of secondary processes. The integrated core study allowed specifying the Cenomanian deposition nature and determining within the field an “odd” different from the other in Western Siberia type of clastic reservoir. The “odd” type is represented by coarse-fine grained shaly (shale content is 12-20%) and sand (12-20% as well) silt stones in the deposits of heterolyte filling of tidal flats. The “odd” nature of deposits is determined by sand material localization as thin lenticular lamina (0.1-3.0 mm; up to 30-40 % for rock) with sharp boundaries and high permeability along the layers. The formation of shaly siltstones with sandy lamina relates supposedly to drought periods and eolation activation which lead to sand storms on the territory of tidal flats.