Hydrogeological features of oil-bearing properties of the Hvizdets oil field (Boryslav-Pokuttia oil and gas region)

The hydrogeological characteristics of the structures of the Hvizdets oil field have been studied. Specific features of the underground waters of the field, which determine the presence of hydrocarbon accumulations, have been identified for potential application in other areas of the investigated region when searching for new deposits. It has been found that in all aquifers of the field, the reservoir pressure exceeds the hydrostatic pressure by a magnitude of 3 to 13 MPa. The highest pressure values are recorded both within the oil- and gas-bearing contour and near the oil-water contact. It has been established that high values of the reservoir water overpressure reflect the dense hydrodynamic isolation of individual aquifers and sections of the Hvizdets oil field and directly indicate their high hydrogeological favourability for preserving deposits. The spatial distribution of hydrodynamic vectors points to potential migration paths of fluids towards both the Bilche-Volytsia zone of the Precarpathian foredeep and the Skyba zone of the Carpathians. The macro-component composition, contents of trace elements, and the component ratios of reservoir waters of the Hvizdets oil field reflect quasi-stagnant hydrogeological conditions, favourable for preserving hydrocarbon deposits here. The presence of bicarbonate-sodium waters of the Menilite sediments with reduced TDS and increased bicarbonate ion content is considered a direct hydrogeological criterion resulting from the reduction of sulfur from sulfates when underground waters interact with hydrocarbons in the dispersion halo of the oil deposit. The gas-hydrogeochemical features of oil presence include the increase in water gas saturation when approaching the deposit and the increase in the relative proportion of methane homologues in the composition of dissolved gases.