Application of the Data on δ13C and δ18O of Carbonates for the Study of Unconventional Reservoirs on the Example of the Bazhenov Source Rocks, Western Siberia, Russia

Abstract

This paper addresses potential application of data on stable carbon and oxygen isotope composition of carbonates for study of organic rich source rocks on the example of the Late Jurassic–Early Cretaceous Bazhenov Formation (West Siberian petroleum basin, Russia). Geochemical studies were conducted for sections located in central (most productive) and peripheral (northern and southern) regions of the Bazhenov Formation distribution area, containing deposits formed under different conditions. We identified key factors impacting stable isotope composition of carbonate minerals and established relation of their isotope composition to the formation conditions. Using a thermodynamic model of carbon and oxygen isotope exchange in the carbonate–water–carbon dioxide system, it is shown that variations in the isotope composition of secondary carbonates are affected by isotopic composition of primary carbonates in sediments and by the isotope exchange reactions with water and carbon dioxide, generated during the source rocks transformation. Our results demonstrate that stable isotope data for carbonates in the Bazhenov Formation together with standard geochemical methods can be efficiently applied to determine sedimentation conditions and secondary alteration processes of oil source rocks.

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

“…Other samples with C carb not exceeding 1 wt.% are essentially depleted in 18 O, and the δ 13 C carb values of these samples vary from −0.4 to −16.6‰. We suggest that the original isotopic composition, characteristic for sea water carbonates, was changed in carbonates of the investigated section in diagenesis and catagenesis, when the secondary carbonatization could take place at elevated temperatures in the presence of isotopically light CO 2 derived from the organic matter [55]. The layers with low carbonate content are mostly affected by secondary processes.…”

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].…”

“…Yurchenko et al [4] address the potential application of stable carbon and oxygen isotope composition of carbonates for the study of the organic-rich source rocks genesis on the example of the Upper Jurassic-Lower Cretaceous Bazhenov Formation (West Siberian Basin, Russia). The studied deposits are located in the central (the most productive) and peripheral (northern and southern) regions of the Bazhenov Formation distribution area, as an example of the different sedimentation conditions.…”