The development of hard-to-recover reserves in regions with developed oil production infrastructure is of great practical importance. In oilfields with traditional reservoirs, it is economically advantageous to add unconventional reservoirs from the underlying horizons to the development. The characteristic of such reservoirs is important for the competent use of secondary methods for enhanced oil recovery. One of the problems is to assess the hydrophobicity/hydrophilicity of the rocks which are composed not only of different minerals in various proportions, but also of organic matter. Laboratory studies of low-permeability reservoirs of the West Siberian petroleum basin carried out using a complex of lithological, petrophysical and geochemical methods make it possible to solve this problem as well as increase the reliability of searches for new hydrocarbon reservoirs and reduce risks during their development. Rock samples from the Upper Jurassic-Cretaceous sedimentary section of low-permeable deposits were studied using the X-ray diffraction method (mineral composition), the pyrolytic Rock-Eval method (organic matter) and the Pfeffer and HexCo methods (cation exchange capacity). The study of the physic-chemical activity of the mineral surface of such formations as the Frolov, Bazhenov, Abalak, Achimov showed that clay, siliceous minerals and organic matter could form organomineral aggregates during sedimentation. Analysis of interaction of humic material into mineral matrix during diagenetic and catagenetic stages showed 2 mechanisms of interaction with molecules: intrusion (immobilization) into a mineral volume (hydrolysis and polycondensation) and adsorption at a mineral surface (hydrogen and covalent bonds). The factor of intrusion of organic matter into the silica requires special attention during the study of wettability of rocks and making decisions on the development of oil and gas bearing formations of unconventional low-permeable reservoirs.
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