GEOCHEMISTRY AND CARBON ISOTOPE CHARACTERISTICS OF ASSOCIATED GASES FROM OILFIELDS IN THE NW GREATER CAUCASUS, RUSSIA

Abstract

The NW Greater Caucasus and surrounding areas have a long history of petroleum production dating back to the mid‐19th century. However the origin of the oil and gas is still a matter of debate. This paper focusses on a study area to the north of the western Greater Caucasus covering the West and East Kuban Basins and neighbouring structural highs where oil and natural gas occur in reservoir units of Neogene, Paleogene, Cretaceous and Jurassic ages. The study is based on the results of organic geochemical and stable carbon isotope analyses of 21 samples of associated gases from 16 oil fields. The gas samples' compositions were investigated together with the δ13C values of C1 to C5 alkanes. Twenty of the gas samples were of thermogenic origin and one was mixed (thermogenic and secondary microbial). δ13C values for CH4 for all the gas samples varied over a wide range from ‐62.3 to ‐30.0 ‰, indicating major variations in the thermal maturity of the respective source rocks.