Structure of lower-cambrian abakunskaya formation (South-Tungusskaya oil-and-gas bearing region, Leno-Tungusskaya oil-and-gas bearing province)

Background. The research object was the Lower-Cambrian Abakunskaya Formation located in the South-Tunguskaya oil-and-gas bearing region of the Lena-Tunguskaya oil-and-gas province.

Aim. To compile a sedimentary-capacity model of the Abakunskaya Formation and identify relationships between the identified lithological rock types and their filtration-capacity properties in order to refine the oil and gas potential of the region.

Materials and methods. Geological and geophysical data collected from deep wells drilled in the area of work were used, along with published and archival materials on the geological structure of the South Tunguska oil and gas region. The factual material on 24 wells that opened the Abakunskaya Formation includes descriptions of cores, sludge, and test results. The wells were drilled in 1970—1990; however, detailed descriptions of the core material, core photographs, and core study results, with some contradictory exceptions, are missing. For this reason, the Formation was sectioned based on GIS materials with an analysis of all preserved materials on the wells. Logging diagrams for 20 wells were analyzed. An analysis of changes in the thickness and composition of sediments was carried out. A detailed division of sections into members, correlation of sections, and analysis of changes in the filtration and storage properties of rocks were performed. The developments of the specialists of the All-Russian Research Geological Oil Institute (VNIGNI), which comprise a system of genetic organization of carbonate bodies of various hierarchical levels, served as the methodological basis for this research.

Results. Lithological types of sediments were determined; lithotype associations characterized by common sedimentation conditions were identified; lithological-facies zones were distinguished; and a sedimentation-capacity model of the Abakunskaya Formation was compiled.

Conclusions. The Abakunskaya Formation is represented by carbonate and carbonate-clay deposits of the open-shelf lithological-facies zone, which are relatively consistent in thickness and composition. A sedimentary-capacity model of the Abakunskaya Formation in the western part of the South Tunguska oil-and-gas bearing region has been constructed. This model reflects changes in the composition and thickness of the deposits, as well as their structural and textural charac- teristics. Oolitic-organogenic-clastic types of carbonates that form accumulative bodies exhibit the highest filtration and capacity properties.

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