LITHOLOGICAL AND PETROGRAPHIC CHARACTERIZATION OF BAZHENOV SUITE RESERVOIR ROCKS IN THE SOUTH-EAST OF THE WESTERN-SIBERIAN PROVINCE (TOMSK REGION)

Abstract

The relevance of this research comes in response to the need to expand the resources of Western Siberia including Tomsk region, by the development of hard-to-recover oil reserves concentrated in the Bazhenov Suite (Tithonian-Berriasian). The aim of the research is to reveal the features of the lithologic composition and structure of the Bazhenov reservoir rocks across the potentially prospective oil-producing Tomsk region. Object: Bazhenov Suite bituminous deposits discovered by drilling at a local elevation in the Tamrat Basin (Nyurol’ sedimentary basin), the Pudinsky oil-and-gas-bearing region of the West Siberian oil and gas province (Tomsk Oblast), where an oil inflow was obtained. Methods: geophysical studies, macroscopy core description, petrographic and X-ray analyzes. Results. The paper introduces spatial distribution of decomposed rocks – oil and gas reservoirs – identified throughout the productive interval of the Bazhenov Suite. The study provides a detailed geophysical and petrographic description of rocks as well as their textural and compositional characteristics. Authors divide all rocks into seven lithotypes: 1) aleurit-silicitic argillites with rare tubicolous shells and «mud eater» fossils; 2) bituminous silicitic argillites with silicious bands and diatoms traces; 3) bituminous radiolarian argillic silicites; 4) bituminous radiolarian silicites with tubicolous shells and silicious bands; 5) bituminous radiolarian argillic silicites marked by bioturbation and crinoid traces; 6) radiolarian silicitic argillites with algae traces; 7) silicitic argillic carbonates. It was found that the accumulation of Bazhenov sediments was controlled by a low-dynamic stagnant sedimentation regime in relatively deep-sea conditions of the reducing geochemical environment. There is a correlation between both the mineral composition and the content of sapropelic organic matter with the transgressive-regressive sedimentation cyclicity: the 4th lithotype is the most enriched in siliceous material and organic matter, and the maximum amount of these components occurs at the point of inversion of the transgressive-regressive cycle. The Bazhenov collector having a mixed genesis was formed during the multi-stage lithogenesis (sedimentogenesis–catagenesis) and poststadial processes. The void space is represented by ultrathin bio-voids and pores as well as by both interlayer and intralayer fractures.

Keywords

• nyurol’ basin
• western siberia
• tomsk region
• tithonian-berriasian
• bazhenov suite
• bituminous argillite
• oil source rocks
• lithotype
• reservoir rock