Eocene and Oligo‐miocene Source Rocks in the Rioni and Kura Basins of Georgia: Depositional Environment and Petroleum Potential

Abstract

For over a century, oil has been produced in Georgia from oilfields located in the foreland basins between the Greater and Lesser Caucasus foldbelts. To date, little information on the associated source rocks has been available. In this context, this paper presents a study of 380 samples of Eocene (Kuma Formation) and Oligocene to Lower Miocene (Maikop Group) source rocks from three outcrop sections in the Rioni and Kura Basins. The Kuma Formation in the Rioni Basin is composed of fully‐marine marls and is about 40 m thick. At the Martivili and Khobi sections, the formation is thermally immature and has an average TOC of 3.2 wt%. The hydrogen indices (HI) of 300–600 mg HC/g TOC indicate that the organic matter is oil‐prone Type II kerogen. The oil generation potential is between 1.0 and 2.4 t HC/m2, and the Kuma Formation is therefore interpreted as a prolific source rock. The Maikop Group in the Rioni Basin was studied at the Martvili section, where it is thermally immature. The Oligocene succession is divided by calcareous shales deposited during the Solenovian Event (at the onset of nannoplankton zone NP23) into Pshekhian and Solenovian‐to‐Kalmykian intervals. The Pshekhian interval (NP21‐22) is over 60 m thick and comprises a marly lower part and a shale‐rich upper part, and contains high quantities (average 2.7 wt% TOC) of Type II‐III kerogen (average HI: 278 mg HC/g TOC). The overlying largely carbonate‐free shale succession, 424 m thick, is less organic matter ‐rich (∼2.0 %TOC) and contains dominantly Type III kerogen (average HI: 140 mg HC/g TOC). In total, the Maikop Group has a generation potential of about 4 t HC/m2, a value which is higher than in most other sub‐basins in the Eastern Paratethys. Because the Rioni Basin continues westwards into the Black Sea, these results are relevant for future exploration in the eastern part of the Black Sea Basin. The Maikop Group in the western Kura Basin in the Tbilisi area is over 3500 m thick and includes numerous sandstone beds. Because of the great thickness of the Maikop Group and the presence of about 3 km of overburden, which was removed during Miocene to Recent unroofing, potential source rocks in the Eocene to Lower Oligocene succession have reached oil window maturities but their hydrocarbon potential is low.

Petroleum Systems in the Rioni and Kura Basins of Georgia

“…In Georgia, reservoir units with varying but often poor quality are considered to be the main problem for hydrocarbon accumulation and production (Nachtmann et al, 2015a). In addition, recent studies that focused on the principal Eocene and Oligocene source rocks (Pupp et al, 2018;Sachsenhofer et al, 2018a, b; also varies strongly both vertically and between the Rioni and Kura Basins. Apart from conventional oil and gas, Jurassic highvolatile bituminous coal in the Tkibuli-Shaori region (located NW of the Dziruli Massif: Fig.…”

“…Most of these new source rock and hydrocarbon samples were made available by Georgian Oil and Gas within the context of their ongoing exploration activities. In a final section, the new data together with published source rock (Pupp et al, 2018) and oil data (Robinson et al, 1997;Mayer et al, 2018) are used to determine oil families, to support oil-source correlations, and to define petroleum systems.…”

Exploration Plays in the Caucasus Region

“…Similarly, the source and charge elements of the petroleum systems are not discussed. The main effective source rocks in the Greater Caucasus area, such as the Middle-Upper Eocene Kuma Formation, Oligocene -Lower Miocene Maykop Group, and Middle-Upper Miocene Diatom Formation, have been systematically described by authors including Abrams and Narimanov, 1997;Feyzullayev et al, 2001;Isaksen et al, 2007;Sachsenhofer et al (2017Sachsenhofer et al ( , 2018Sachsenhofer et al ( , 2021 this issue), Yandarbiev et al (2017a,b;2021 this issue), Gavrilov et al (2017Gavrilov et al ( , 2021 this issue), Vincent and Kaye (2018), Mayer et al (2018), Pupp et al (2018), Aghayeva et al (2021 this issue), Boote et al (2018) and Oblasov et al (2020).…”

Tectonic Evolution of the Northern Margin of the Cenozoic Ararat Basin, Lesser Caucasus, Armenia

“…Gabrielyan et al, 1981;Phillip et al, 1989). Oil has been produced from the Rioni and Kura Basin for over a century, and Eocene and Oligocene to Lower Miocene source rocks were recently investigated by Pupp et al (2018).…”