LITHOFACIAL CHARACTERISTIC AND PETROLEUM POTENTIAL OF THE OSINSKY PRODUCTIVE HORIZON OF THE BOLSHETIRSK DEPOSIT (EASTERN SIBERIA)

Abstract

The relevance. Eastern Siberia is an area with large hydrocarbon resources that play an important role in the development of the Russian oil and gas complex. The terrigenous Vendian was the main object of prospecting and exploration in this area for a long time. However the commercial oil and gas potential of the Vendian–Lower Cambrian carbonate complex with a complicated structure and intense variability of reservoir properties has been proven in recent decades. In this relation a detailed study of the lithological factors of the formation of carbonate reservoirs is necessary for the optimal development of deposits confined to this complex. The object: carbonate deposits of the Osinsky productive horizon of the Lower Cambrian, exposed by deep drilling at the Bolshetirsk deposit. The aim of the research is to identify the levels with the best reservoir properties on the basis of lithofacies analysis. Methods: mineralogical and petrographic study of core material and typification of sediments; facies analysis of lithological types (lithotypes) of rocks; correlation of reservoir properties with different lithotypes. Results. It was established that Osinsky horizon is characterized by a heterogeneous structure due to the periodic change of environments on the shallow shelf: from tidal plains and sebkhs to shallows and biohermal buildups of the upper sublittoral. It was shown that differences in sedimentation conditions affected the structure of the primary void space. However the post-sedimentation processes became the determining factor in the formation of reservoir properties, but their role was ambiguous. It was found that the secondary mineralization of voids practically destroyed the reservoir potential of bar and bioherm deposits with highest primary porosity. The level of development of the highest-capacity reservoir is confined to the most dolomitized sediments of the littoral zone.

Keywords

• eastern siberia
• osinsky productive horizon
• lithology
• reservoirs
• lower cambrian