Middle Miocene (Sarmatian) sandstones in the Ukrainian Carpathian Foredeep are important exploration targets for natural gas. In this paper, we report on petrophysical studies on core samples of these sandstones with which we integrate wireline log data from 42 boreholes. Sarmation siltstones and sandstones in the study area are assigned to the lower part of the Dashava Formation. Seventeen units (LD 17 to LD 1:0.05 to 5m thick) are recognized in this formation on the basis of lithostratigraphy and log response. Sandstone content is highest within three lithostratigraphic complexes corresponding to units LD17‐LD14, LD9‐LD8 and LD5‐LD3.
During the Sarmatian, the Carpathian Foredeep was characterized by two depositional systems: a basinal turbidite system, and a second, more mixed system. Important controls on sedimentation included basin configuration and water depth, the occurrence of turbidity and other currents, and the location of provenance areas. Clastic material was delivered to the basin by rivers and ephemeral streams mostly from the Carpathian foldbelt. The content of sandy material within the Sarmatian succession increases from NW to SE, and from the central portion of the Krukenychy depression to the margins of the basin.
The formation of the temperature regime of the Dnieper-Donets depression is determined by the magnitude of the deep heat flux, the structural and tectonic features of the region, the lithology of the sedimentary complex, the occurrence of a thick complex of chemogenic and volcanic rocks in the region, as well as hydrogeological conditions. Based on the analysis of factual geothermal material on wells, obtained during geophysical studies, measurements of temperatures and geothermal gradients, measurements of temperatures during testing of productive horizons, as well as from literary sources, the interpolation of factual geothermal material is carried out. The geothermal parameters characterizing the temperature state of rocks and fluids of different tectonic zones of the Eastern oil- and gas-bearing region have been determined. Schemes of temperature distribution at depths of 2000, 8000 m, average geothermal gradient, depths of isotherms 150 °C, 180 °C are given and regularities of distribution of geothermal parameters are analyzed. The lateral zoning of the geothermal parameters distribution of the region is established, the zones of their maximum, middle and low values are distinguished. Taking into account the peculiarities of the tectonic structure of the Dnieper-Donets graben, as the sedimentary complex is submerged, a gradual replacement of oil by oil and gas fields and then by the gas ones occurs from the northwest to the southeast. Geothermal parameters characterize the geothermal activity of the subsurface and allow to determine its zonation, as well as to predict the phase state of hydrocarbon systems at great depths.
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