STRUCTURAL FEATURES AND FORMATION CONDITIONS OF EARLY FAMENIAN RIFFOGENIC SEDIMENTS IN THE SOUTHERN PART OF THE DENISOV DEPRESSION OF THE TIMAN-PECHORA OIL AND GAS PROVINCE

Abstract

Relevance. Currently, due to the growth of hard-to-recover resources and hydrocarbon reserves, the study of carbonate rocks of complex structure, in particular the Zadon-Eelets sediments of the Upper Devonian-Tournaisian oil and gas complex of the Denisov depression of the Timan-Pechora oil and gas province, is becoming more relevant. As it is known, the Devonian period in the history of the Timan-Pechora basin is of great importance due to the extensive development of reef sediments, which represent potential zones of oil and gas accumulation. The study of the general features of the structure and the analysis of materials based on the results of macro- and micropetrographic studies of the core will allow reconstructing the facies zonality and paleogeographic conditions of sedimentation of the Zadon-Eelets reef structures as promising objects for the search for oil and gas fields. Aim: study the general features of the structure and lithological and petrographic features of the Zadon-Eelets riphogenic sediments of the Denisov depression, in order to reconstruct their facies zonality, environments and conditions of formation. Objects: Zadon-Elets riffogenic sediments of the Famennian Stage of the Upper Devonian in the southern part of the Denisovsky depression of the Timan-Pechora oil and gas province. Methods: lithological-facies analysis and paleogeographic reconstructions based on the analysis of materials, including a complex of geophysical studies of wells, photographs of columns and sections core, the results of the study of carbonate content rocks, lithological-sedimentological description of the core, as well as photographs and micropetrographic description of the thin rock section. Results. The paper introduces the results of the study of Early Famenian riphogenic sediments, which are potential zones of oil and gas accumulation in the south of the Denisov depression of the Timan-Pechora oil and gas province. The variability of rocks by section and area of the studied area was traced, which made it possible to identify four lithotypes of rocks that are combined into two groups. The material composition of rocks was studied based on the analysis of definitions of carbonate content. The rocks are composed of carbonate minerals – calcite and dolomite – by 93–98 %. Macro- and micropetrographic analysis of structural and textural features of lithotypes using the well-known model of standard facies belts, developed by J. Wilson, allowed reconstructing the facies conditions of sedimentation of the Early Famenian sediments. Rocks were accumulated in three facies zones of the shallow-shelf carbonate platform: an advanced slope, a microbial hill and shallow water, which determined their complex polyfacial structure.

Keywords

• facies
• lithologic-facial zoning
• famennian deposits
• upper devonian
• denisov depression
• timan-pechora oil and gas province