Distribution and material composition of the Devonian organic-rich rocks of the Volyn-Podillia plate

Abstract

The Volyn-Podillia plate is one of the main oil and gas-bearing regions of Ukraine. Despite numerous geological and geophysical studies of these territories, they still remain underexplored, and their oil and gas potential is underestimated. To date, two gas fields, Lokachynske and Velykomostivske, have been discovered within the boundaries of the Volyn-Podillia plate in the Middle Devonian sequence. Despite the established commercial gas bearing, the Devonian strata within the Volyn-Podillia plate are currently not sufficiently studied from the point of view of the occurrence of the organic-rich rocks in the section, which could generate hydrocarbons. A significant amount of collected core material and geological-geophysical data from numerous wells within the research area made it possible to study the features of distribution and conduct a mineralogical-petrographic and geochemical study of Lower, Middle and Upper Devonian organic-rich rocks. In the sediments of the Lochkovian stage of the Lower, Eifelian and Givetian stages of the Middle and Frasnian stage of the Upper Devonian, the organic-rich rocks have been established. They are represented by terrigenous, clayey and carbonate strata. In the section of the Lower Devonian, they are represented by clay-carbonate and carbonate rocks within the Lochkovian stage. The organic carbon content in these rocks reaches 0.45 %. In the Middle Devonian, organic-rich rocks occur in sections of both the Eifelian and Givetian stages, being represented by terrigenous, clayey, and carbonate rocks. The organic carbon content in the rocks of the Eifelian stage reaches 0.65 %, and in the rocks of the Givetian stage – 2.34 %. In the sections of the Frasnian stage of the Upper Devonian, organic-rich rocks are represented by terrigenous, clayey and carbonate layers with organic carbon content of up to 1.43 %. Given the occurrence of organic-rich rocks in the sections of the Lower (Lochkovian stage), Middle (Eifelian, Givetian stages) and Upper Devonian (Frasnian stage), these deposits can be considered as potentially oil and gas generating, which could have been a component of the Paleozoic petroleum system of the Volyn-Podillia plate.