GEOCHEMICAL CHARACTERISTICS OF ORGANIC MATTER IN CRETACEOUS-CENOZOIC SOURCE ROCK STAGES OF THE NORTH-EASTERN PART OF THE LAPTEV SEA BASED ON THE RESULTS OF SHALLOW STRATIGRAPHIC DRILLING
Z. A. Tembotov1,4, N. A. Malyshev2, V. E. Verzhbitsky2, A. A. Borodulin2, V. V. Obmetko2, D. K. Komissarov2, A. A. Kolyubakin3, A. V. Stupakova4, M. A. Bolshakova4, A. A. Suslova4, A. G. Kalmykov4, N. V. Pronina4, E. A. Krasnova4,5, R. M. Gilaev4, A. V. Mordasova4, I. V. Kuvinov4
Arctic Scientific Center LLC, Moscow, Russia
2Rosneft Oil Company, Moscow, Russia
3LLC "RN-Exploration", Moscow, Russia
4Lomonosov Moscow State University, Moscow, Russia
5Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia
Keywords: stratigraphic drilling, new wells in the Arctic, Laptev Sea basin, source rock, generation potential, organic matter, maturity
Abstract
The Laptev Sea sedimentary basin is located in the eastern part of the Russian Arctic shelf and has been fairly well studied by geophysical methods, but until recently, drilling data were lacking. In 2021, six new stratigraphic wells were drilled on the Laptev Sea shelf north of the Anzhu Islands by order of PJSC NK Rosneft. As a result, unique core material was obtained, which was studied using a wide range of analytical methods. This article is devoted to the analysis of the geochemical characteristics of the oil and gas source rocks (OGSR) of the Cretaceous-Cenozoic complex, which in the Laptev Sea basin can be considered as a potential for hydrocarbon generation. The paper presents the main pyrolysis parameters characterizing the proportion of free hydrocarbons in the rock (S1), oil generation potential (S2), maturity (Tmax), as well as the maceral composition of rocks and vitrinite reflectance (VR). As a result, it was established that carbonaceous and clayey-siltstone rocks of the Paleocene-Eocene complex are enriched in organic matter (OM) containing up to 20% of the lipid component and are capable of independently generating not only gaseous but also liquid hydrocarbons. Unlike the OM of the rocks of the Paleocene-Eocene complex, the OM of the Lower Cretaceous strata is at a much higher stage of transformation, which corresponds to the peak of the "oil window" and the beginning of the main phase of gas formation MK2-MK4. The accumulation of OM occurred in various lithofacies conditions; both humic type III kerogen and mixed type II-III kerogen are found in the rocks. Based on the drilling results and studies conducted in the section of the sedimentary cover of the aquatic part of the Laptev Sea, factual data on the characteristics of oil and gas source rocks were obtained for the first time, which can be used to predict the oil and gas potential of both the Laptev Sea basin and the entire East Arctic region.
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