Home > Archive > No. 3–4 (191–192) 2023 > 7–19
Geology & Geochemistry of Combustible Minerals No. 3–4 (191–192) 2023, 7–19
https://doi.org/10.15407/ggcm2023.191-192.007
Yaroslav LAZARUK, Myroslav PAVLYUK
Institute of Geology and Geochemistry of Combustible Minerals of National Academy of Sciences of Ukraine, Lviv, Ukraine, e-mail: igggk@mail.lviv.ua
Abstract
The southern part of the Dobrogea Foredeep is located in the southwestern regions of Ukraine within the Odesa region. Here, on the territory of the uplifted Bilolissya block, the East Sarata, Zhovtyjar, Saryjar, Zarichna oil accumulations are located in the chemogenic-carbonate layer of the Middle and Upper Devonian. The deposits are confined to limestones and dolomites with secondary fractured-cavernous-porous reservoirs. They lie at depths of 2500–3200 m. During the test of two dozen wells, the filtrate of the drilling fluid with a small amount of oil was received with the estimated flow rates of several tons per day. The rise of the oil level in the wells was quickly stopped, the hydrodynamic connection of the wells with the productive formations was lost. The use of today’s known methods of intensification of the flow of hydrocarbon fluids did not lead to positive results. According to the research of microphotographs of reservoir rocks, it is proved that the largest voids of reservoir rocks are filled with immobile bitumen, while the smaller cavities contain mobile oil. Immobile bitumen fills main channels and blocks communication between rock cavities. This is the main reason for the absence of industrial inflows of oil to the wells. Another important reason is the low filtering properties of the collectors. Most of them have a permeability of less than 0.01∙μD. Other reasons for the failure of the industrial development of oil deposits are the high dynamic viscosity of oil due to the high content of asphaltenes, silicagel resins, paraffins, the low energy potential of oil deposits due to their degassing during the long geological time, as well as the lack of hydrodynamic connection of oil deposits with natural water pressure systems. We assume that the Middle and Upper Devonian oil fields of the Western Fore-Black Sea area are most likely mainly bituminous. Given the significant depths of the deposits, their industrial development is technically impossible today. Therefore, it is impractical to plan further scientific research on the mentioned complex. Instead, research should be reoriented to the Silurian terrigenous-carbonate complex and the Lower Devonian terrigenous complex, which are hydrodynamically more closed and in which non-degassed hydrocarbon accumulations can be preserved.
Keywords
oil, bitumen, deposit, oil traps, carbonate reservoir, terrigenous complex, hydrocarbon reserves, exploration and development of deposits
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