The Upper Devonian shales are predominantly carbonate, carbonate-siliceous thin-layer rocks with a high content of organic matter. Considered formation is widespread within the Volga-Ural and Timan-Pechora basins in the European part of Russia. Various estimations show that the hydrocarbon resources of the Upper Devonian shales range between hundreds of millions to billions of tons of oil. However, recovery of such hydrocarbons is significantly constrained due to the high heterogeneity and complex structure of rocks and its pore space. The paper presents the results of complex lithological studies of Upper Devonian shales based on core material from two wells located in the northern part of the Verkhnekamsk depression. Study includes data obtained with a scanning electron microscopy (SEM), X-ray structural analysis, optical microscopy, nuclear magnetic resonance (NMR) and Rock-Eval pyrolysis method. Analyzed rock samples mainly represent mixed carbonate-siliceous differences with a significant content of organic matter. A total of 11 lithotypes were identified and grouped by the predominant component (carbonate, siliceous), structure, and probable genesis. Within each group, a specific set of void space types were allocated. Only minor part of pores was associated with a mineral matrix; it was shown that the majority of void space is concentrated in the organic-mineral association (a polymer compound of organic matter and mineral component). Images obtained from scanning electron microscope show that the pore size in rock samples varies from 1 to 10 μm. And there is a strong connection between amount of organic matter and porosity coefficient.