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The article examines the reasons for the formation of vertical hydrochemical inversion within particular oil and gas basins and points out the role of waters of different genesis in the development of this phenomenon. The following processes of reverse hydrochemical zoning in the sedimentary cover are analyzed: thickening of heavy clay strata and the related squeezing of loosely bound waters, dehydration of clay minerals and catagenic fluid generation accompanying the transformation of organic matter into hydrocarbons of the petroleum series. The hydrochemical inversion at great depths is noted to occur and persist in the environment of the passive hydrodynamic regime; in closed water-drive systems, the demineralization of waters with depth causes the decrease in the hydrodynamic potential gradient, determining the migration pattern not only of water but also of hydrocarbons and, consequently, the location of oil and gas accumulation zones.

The features of the chemical composition of formation waters of the Upper Permian, Lower and Middle Triassic aquifers within individual structures of the Malozemelsk-Kolguev monocline of the Timan-Pechora oil and gas bearing basin are examined. It is shown that the aquifers that, despite their remoteness from the recharge areas, had experienced repeated processes of dipping and uplifting of the territory, preserved the infiltration waters, but significantly transformed ones. To identify their genetic profile and determine the relationship with the processes of catagenetic changes, hydrochemical coefficients and indices of water saturation of calcium carbonate and calcium sulfate are calculated. It is established that the examined infiltration waters are characterized by high aggressiveness, dissolution ability, leaching and removal of main minerals. It is pointed out that the consequence of these processes is the formation of secondary void space and the creation of high capacitive and filtration properties of rocks. The universality of geochemical interaction between water and rocks in thermodynamically open geological systems is emphasized and it is confirmed by individual geological examples that the heterogeneity of the hydrochemical field can act as a cause of screening zones of oil and gas accumulation, as well as provide appropriate conditions for localization of hydrocarbon fluids.