Genetic Types of Crude Oil in the Eastern Part of the Crimea–Caucasus Area

Abstract

The paper presents data on 48 samples of crude oil and oil shows from oil fields and surface oil seeps in the Krasnodar Territory, Crimea, and the Russian part of the Black Sea. The oil samples were analyzed for isotope and molecular composition. According to the results, all crude oil samples were classified into three genetic types (Akhtyrsky, Sladkovsky, and Nikolaevsky), which differ in molecular and isotope composition and were derived from different types of source organic matter. A source rock was identified only for the Akhtyrsky genetic type (type 1): these were rocks of the Middle Eocene Kuma Formation and the Oligocene rocks of the Lower Maikop Group. The source rock for the Sladkovsky genetic type (type 2) of the oils may have been Lower Miocene rocks of the Middle and Upper Maikop Group, which occur at depths greater than 4000 m in the central part of the West Kuban basin. The source rocks of Nikolaevsky genetic type (type 3) of the oils may have been older rocks, no younger than of Early Cretaceous in age. It is demonstrated that the Cenomanian–Turonian rocks, which are often considered to be among the dominant source rock for oil in this area, most likely could not make any significant contribution to the oil and gas potential because the thicknesses of these rocks are very small, and also because no molecular and isotopic signatures of their organic matter are found in the crude oils and oil shows.