Alginite-Rich Layers in the Bazhenov Deposits of Western Siberia

Abstract

In this study, we identified the luminescent layers containing a significant amount of alginite in the Upper Jurassic–Lower Cretaceous Bazhenov Formation named “the alginite-rich layers”. Lithological and geochemical methods were used to determine distinctive features of these layers and to evaluate their impact on the total petroleum generation potential of the Bazhenov Formation. We have shown that the composition of the alginite-rich layers differs significantly from the organic-rich siliceous Bazhenov rocks. Rock-Eval pyrolysis, bulk kinetics of thermal decomposition, elemental analysis, and the composition of pyrolysis products indicate type I kerogen to be the predominant component of the organic matter (OM). Isotope composition of carbon, nitrogen, and sulfur was used to provide insights into their origin and formation pathways. The luminescent alginite-rich layers proved to be good regional stratigraphic markers of the Bazhenov Formation due to widespread distribution over the central part of Western Siberia. They can also be applied for maturity evaluation of the deposits from immature to middle of the oil window, since the luminescence of the layers changes the color and intensity during maturation.

Provenance and the U–Pb age constraints on the tuff beds of the Late Jurassic–Early Cretaceous Bazhenovo Formation, West Siberian Basin

“…This paper presents new data on the zircon U-Pb dating of the tuff beds in the Bazhenovo Formation. The findings from the current study add to the previous studies on the numerical age of the tuffs and their provenance (Panchenko et al, 2021;Rogov et al, 2023).…”

“…The studied tuff beds in member 4 are assigned to the latest middle Volgian Praechetaites exoticus Zone (Rogov & Zakharov 2011;Rogov et al, 2023). Recent publications indicate the presence of a series of tuff layers in members 3 and 5 of the Bazhenovo Formation (Panchenko et al, 2021(Panchenko et al, , 2022. However, due to their extreme thinness (1-3 mm), they are very difficult to select for analysis without contaminating the sample with host rock and therefore were not used in this study.…”

“…All of the tuff samples were selected based on their purity to avoid the potential for considerable interference from the host organic-rich shales. These tuffs represent T1 tuff based on the classification by Panchenko et al (2021). Due to bed thinness (<1 cm) and the small amount of available pyroclastic materials, not all samples were analysed.…”

A Summary of “Petrophysics and Geochemistry of Unconventional Reservoirs”

“…Much attention is paid to the study of the kerogen chemical structure [7], variation of kerogen type on the depth [8], the interaction of the organic matter and mineral matrix [9], void space [10], and the kerogen-related multiscale heterogeneity and anisotropy [11] of the Bazhenov formation sediments.…”

“…Bulatov et al [8] have discovered the luminescent layers containing a significant amount of alginite in the Upper Jurassic-Lower Cretaceous Bazhenov Formation (West Siberia, Russia). The composition of the organic matter in so-called "alginite-rich layers" differs significantly from that in the organic-rich siliceous Bazhenov rocks.…”