Structure of the moktakon formation of the lower cambrian (Yuzhno-Tungusskaya oil and gas region, Leno-Tungusskaya oil and gas province)

Background. The structure of the Lower Cambrian Moktakon Formation extended across the Yuzhno-Tungusskaya oil and gas region of the Leno-Tungusskaya oil and gas province is studied.

Aim. To develop a sedimentation and storage capacity model of the Moktakon Formation with the purpose of clarifying the oil and gas bearing potential of the region and to elucidate the relations between the selected lithological types and their filtration and storage capacity properties.

Materials and methods. Geological and geophysical data on deep boreholes drilled in the area under study, as well as published and stock materials on the geological structure of the Yuzhno-Tungusskaya oil and gas bearing field were used. Data on 22 boreholes that penetrate the deposits of the Moktakon Formation include: core and cuttings descriptions, test results. Logging diagrams for 15 boreholes that penetrate the Formation to its full thickness were analyzed. Changes in the thickness and composition of the Moktakon Formation sediments were analyzed. A detailed division of the sections into packs, along with correlation of sections and analysis of changes in the filtration and storage capacity properties of rocks, were performed. The methodological basis was formed by works conducted at the All-Russian Research Institute of Oil Geology (VNIGNI).

Results. Lithologic types of sediments and section types were determined. Sedimentation conditions were established, including lithologic and facial zones. A sedimentation and storage capacity model of the Moktakon Formation was developed.

Conclusion. The data obtained by analyzing boreholes that penetrate the Moktakon Formation in the western part of the Yuzhno-Tungusskaya oil and gas field were used to compile a sedimentation and storage capacity model of the studied area. This model reflects changes in the composition and thickness of sediments, as well as their structural and textural characteristics. Biohermal, lagoonal, plume, and slope lithologic-facial zones were identified. The suggested sequence reflects the profile of carbonate sedimentation from lagoonal beyond the reef to slope deposits. Biohermal deposits and clastic carbonate sediments of the upper part of the slope are characterized by the best filtration and storage capacity properties.

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