Prediction of oil and gas within the boundaries of salt structures of the Dnieper-Donets depression on the basis of paleogeothermal reconstructions

Abstract

The Dnieper-Donets depression is the main oil and gas region of Ukraine. The main deposits of hydrocarbon in the depression are confined to the Carboniferous and Lower Permian deposits. Promising oil and gas complexes are Devonian and Pre-Cambrian. The depth of the productive complexes varies from 400 to 6300 m. Clay and saline strata are the regional covers. The reservoirs are sandstones, siltstones, gravelites, and cracked cavernous chemogenic deposits, and in some places, cracked rocks of the crystalline foundation of the depression. Oil and gas deposits are confined to local structures, mainly block and salt dome rocks. The most important of hydrocarbon generation conditions is the degree of catagenesis of sedimentary rocks and the organic matter dispersed in them. The leading factor of catagenesis is geothermal. Temperature levels control the initiation, development and extinction of gas and especially oil formation processes. Geotemperatures have the value of a generation and conservation factor. The patterns of distribution of temperature regimes in deposits are used as one of the criteria for identifying oil and accumulation zones. The temperature interval of the main zone of oil and gas formation (“oil windows”) corresponds to the conditions of the Dnieper-Donets oil and gas region from 90 ºС to 190 ºC. The aim of the study was to create a reconstruction of paleogeothermal regimes to establish the depth position of the main zones of oil and gas formation within the inter-stock depression of the Vysachkivsko-Romodanivska salt anticline (southern near-flank zone), the Skorobagatkivska salt brachyanticline (axial zone), the Herasimivska salt structure (northern near-flank zone) of the central part of the Dnieper-Donets depression. The performed researches were carried out on the basis of paleogeothermal graphs and dip graphs of stratified strata, which coincide in depth and geological time. The geothermal history of the region is taken into account when assessing the oil and gas potential. The analysis of the graphs showed that the optimal conditions for the generation of hydrocarbons existed for the Middle and Upper Devonian deposits of the Vysachkivsko-Romodanivska structure; for Lower and Middle Carboniferous deposits of the Skorobagatkivska structure; for the Middle Devonian deposits of the Herasimivska structure. Depth intervals of oil and gas generation in the well 402-Kremyankivskaya – from 1180 to 4120 m; in the well 2-Skorobagatkivska – from 3080 to 6960 m; in the well 1-Herasimivska – from 1180 to 4120 m.

Keywords

• dnieper-donets depression
• salt structure
• stage of catagenesis
• oil generation zone
• paleogeothermal
• oil and gas potential