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.
Highlights
Carbonatization of primary non-carbonate oil source deposits occurs at all stages of their post-sedimentation history
In the current study we analyzed the relation between isotope composition of oxygen and carbon in carbonates and the conditions of oil source rocks formation and transformation on the example of the Bazhenov Formation
The studies were performed for three sections of the Bazhenov Formation located in the central, southern and northern regions of the West Siberian petroleum basin using previously published data on this geological object
Summary
Carbonatization of primary non-carbonate oil source deposits occurs at all stages of their post-sedimentation history. Data on the oxygen isotope composition provide information on genesis of reservoir water as well as on temperatures of carbonatization processes [16,17,18,19,20,21,22,23]. Isotope data on carbonate minerals provide information on genesis, formation conditions and potential productivity of unconventional reservoirs. In the present work we analyze the potential of methods based on carbon and oxygen isotope compositions of carbonates for study of unconventional reservoirs on the example of the Bazhenov Formation (West Siberian petroleum basin, Russia)—one of the richest petroleum source rocks in the world. The studies were performed for rock samples of three different sections from different parts of the basin, central (most productive) and peripheral (northern and southern), characterized by different sedimentation conditions
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