Wettability of the rock surface is an important parameter. Wettability of the rock surface is a key parameter which determines the development efficiency of any field. Effective solution of such problems as evaluation tasks of reservoir properties, simulation of two-phase filtration processes, determination of oil recovery factor, substantiation of formation and bottom oil area stimulation methods is associated with the adequacy of the existing concepts of wettability determination and the real wettability of the formation. However, the established ideas about wettability, laid down in standards and techniques, were based on research conducted in the last quarter of the XX century and currently need to be updated, as it was based on homogeneous type of wetting. Thus, substantiating of the new perception about wettability and determination methods is an actual task for effective enhancement of oil and gas fields development. In this paper the results of theoretical and experimental studies of the effect of the pore space microstructure on the hydrophobization of oil and gas reservoirs are presented. A new type of heterogeneous wettability – microstructural wettability, and a possible mechanism of formation is described here. The mechanism of the microstructural wettability formation demonstrates that hydrophobization of the inner pore space in mixed wettability can be associated either with large or small pore sizes. It was proven experimentally that the process of hydrocarbon adsorption depends on the shape, size, and distribution of pores, the mineralogical composition (particle composition and size, presence of clay), as well as on the time of contact of hydrocarbons with the inner pore surface. The concept of the hydrophilic nature of rock prior to the migration of oil into it can be considered as accurate. However, as was shown in the experiments, oil can present in the small pores (up to 10 μm), which is especially significant for the carbonate reservoirs.

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The article presents experimental and theoretical study of the influence of the microstructure of the pore space on the hydrophobization oil and gas reservoirs. A possible mechanism of formation of microstructural wettability are described. The adsorption of the hydrocarbons can be both in small and large size pores. It was experimentally proved that hydrocarbon's adsorbtion depends on the form, size and distribution of pores, type of the mineral surface, how long oil was in contact with the mineral surface.

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The article presents the methodology of the approach to substantiate the coefficients of residual oil saturation and displacement of oil by water (hereinafter Kro and Kdis). A functional dependency that is not included in the GD “Rules for the preparation of technical projects for the development of hydrocarbon deposits” is recommended for use.