Upper Jurassic–Lower Cretaceous Source Rocks in the North of Western Siberia: Comprehensive Geochemical Characterization and Reconstruction of Paleo-Sedimentation Conditions

Abstract

The present work is devoted to geochemical studies of the Bazhenov Formation in the north of the West Siberian Petroleum Basin. The object is the Upper Jurassic–Lower Cretaceous section, characterized by significant variations in total organic carbon content and petroleum generation potential of organic matter at the beginning of the oil window. The manuscript presents the integration of isotopic and geochemical analyses aimed at the evaluation of the genesis of the rocks in the peripheral part of the Bazhenov Sea and reconstruction of paleoenvironments that controlled the accumulation of organic matter in sediments, its composition and diagenetic alterations. According to the obtained data, the sediments were accumulated under marine conditions with a generally moderate and periodically increasing terrigenous influx. The variations in organic matter composition are determined by redox conditions and terrigenous input which correlate with the eustatic sea level changes during transgressive/regressive cycles and activation of currents. Transgression is associated with an intensive accumulation of organic matter under anoxic to euxinic conditions and insignificant influence of terrigenous sources, resulting in the formation of rocks with oil-generating properties. During the regression periods, the terrigenous sedimentation increased along with the dissolved oxygen concentration, and deposits with low organic matter content and gas-generating properties were formed.

Uranium in Source Rocks: Role of Redox Conditions and Correlation with Productivity in the Example of the Bazhenov Formation

“…In particular, Figure 4 shows the correlation of uranium content with vanadium content for well 1. We also observe (Figure 5) a correlation uranium concentration with the Mo/(Mn + Mo) ratio (well 2), one of the most sensitive indicators of redox conditions for the BF rocks [36][37][38][39]. According to the obtained results, uranium content variations strongly correlate with parameters indicating redox conditions at the sedimentation stage, such as oxygen index, vanadium, molybdenum, Mo/Al, Mo/(Mo + Mn), V/Mo, and V/Cr ratios.…”

“…In particular, Figure 4 shows the correlation of uranium content with vanadium content for well 1. We also observe (Figure 5) a correlation uranium concentration with the Mo/(Mn + Mo) ratio (well 2), one of the most sensitive indicators of redox conditions for the BF rocks [36][37][38][39].…”

“…In particular, Figure 4 shows the correlation of uranium content with vanadium content for well 1. We also observe (Figure 5) a correlation uranium concentration with the Mo/(Mn + Mo) ratio (well 2), one of the most sensitive indicators of redox conditions for the BF rocks [36][37][38][39]. The correlations shown in Figures 2 and 3 indicate a change in redox environments, from slightly oxidizing conditions in the lower part of the BF to reducing in the middle and upper parts of the BF.…”

A Summary of “Petrophysics and Geochemistry of Unconventional Reservoirs”

“…During the last decade, the use of stable isotopes of bio (e.g., hydrogen, carbon, nitrogen, oxygen, sulfur) and trace (e.g., Sm, Nd) elements has become increasingly popular for petroleum exploration, not only in conventional but also in unconventional petroleum basins. Several papers in this Special Issue demonstrate how this approach can be used for investigating the depositional conditions and diagenetic processes during the formation of source rocks [2][3][4] as well as the mechanisms that accompany biodegradation of petroleum hydrocarbons [5].…”

“…Leushina et al [2] report the results of geochemical studies and reconstruction of paleosedimentation conditions of Upper Jurassic-Lower Cretaceous source rocks from the north of Western Siberia (Russia). The rocks are characterized by significant variations in total organic carbon content and petroleum generation potential of organic matter; the maturity is at the beginning of the oil window.…”