Geoelectric heterogeneities of the Pre-Dobrudga Trough a zone of hydrocarbon manifestations

Abstract

For the first time, a geological and geoelectrical interpretation of the three-dimensional model of the Earth’s crust and upper mantle was carried out for the Pre-Dobrudga Trough and adjacent areas. It was based on observations of the Earth’s low-frequency electromagnetic field conducted in 2009―2012 by the National Academy of Sciences of Ukraine. The material confidently indicates that hydrocarbon occurrences are confined to the detected anomalies of high electrical conductivity. These are characterized by subvertical channels (from the surface to 10 km deep) galvanically connected with sediments or sub-vertical contact zones of different resistivity observed not only in the Earth’s crust (10―40 km) but also at crust-mantle depths (40―60 km) and in the upper mantle (110―160 km).The channels may determine the flow of ultra-deep fluids. The geoelectric criteria included maximum thickness of the sedimentary stratum, subvertical rise of electrical conductivity anomalies from the crust-mantle depths or column to the entire thickness of the Earth’s crust, subvertical boundaries of heterogeneities (contacts of different resistivity) in the consolidated Earth’s crust and upper mantle,presence of a highly conductive asthenospheric layer. We identified a significant number of local areas that can be considered promising for hydrocarbon occurrence. The majority of them spatially coincided with the already well-known oil and gas fields ― Skhidnosaratske and Zhovtoyarske, with the explored oil and gas prospective areas (Izmailska, Kyslytska, Prymorska, Shyrokivska), and with those that correspond to the areas of special permits for industrial exploration. However, the newly discovered areas that meet most of the geoelectric criteria, but for which no no information on oil and gas content is publicly available, clearly require additional geological and geophysical studies. It has been shown that zones of high electrical conductivity caused by the presence of deep fluids should be considered as deep centers of hydrocarbon generation and ways of their migration to the upper horizons of the Earth’s crust.