Elision processes as main factors in formation of high-productive carbonate rocks of Vendian-Cambrian deposits in Eastern Siberia

UDK: 553.98
DOI: 10.24887/0028-2448-2020-5-16-21
Key words: Siberian platform, Nepa-Botuoba anteclise, carbonate deposits, Vendian-Cambrian, sedimentation, lithogenesis, basement highs, elizion stage, desalination, poro-perm properties
Authors: N.F. Kayachev (RN-KrasnoyarskNIPIneft LLC, RF, Krasnoyarsk), D.V. Nazarov (RN-KrasnoyarskNIPIneft LLC, RF, Krasnoyarsk), A.D. Shutalev (RN-KrasnoyarskNIPIneft LLC, RF, Krasnoyarsk), N.M. Dadakin (RN-KrasnoyarskNIPIneft LLC, RF, Krasnoyarsk), I.A. Kotelnikov (RN-KrasnoyarskNIPIneft LLC, RF, Krasnoyarsk), N.M. Kutukova (Rosneft Oil Company, RF, Moscow)

The article consider the formation conditions of reservoirs of the pay zones B5. Productive pay zone B5 is characterized by high poro-perm properties of Vendian-Lower Cambrian sediments of the Nepa-Botuobinsky anteclise of the Siberian platform of Rosneft Oil Company. Based on lithological studies of core samples and petrophysical materials, it was established that carbonation rocks of the Lower Ustkut horizon were salinized during the sedimentogenesis and diagenesis stages. This salinization was regional and afacial in nature. The lithogenesis of sedimentary cover rocks and, first of all, sediments of the Nepa Formation of the Vendian was accompanied by elizion processes during the transition of clay sediments to mudstones. At the stage of transformation of clay deposits into mudstones during compaction, buried free and physically bound water is removed from them. The migration of these fluids is determined by the structure of the rigid crystalline basement. An important role in the direction of movement of deep fluids is played by erosion protrusions in the foundation and features of the structural restructuring of the sedimentary cover within them. When reconstructing the conditions of lithogenesis, it was found that, as clay deposits become denser, water is squeezed into permeable sandy beds, in which the fluid will be lateral and directed towards the protrusions due to their geomorphological features. Within the protrusions themselves, increasing pore pressure will lead to subvertical fluid migration. In the process of vertical fluid migration, the elution solutions, reaching the level of salinized dolomites of the B5 layer directly above the ledges of the foundation, will dissolve, first of all, halite. Thus, the formation of reservoirs with high poro-perm properties is a consequence of the local desalinization of carbonate rocks of the Vendian-Cambrian during the elizion processes of background lithogenesis. Studying and establishing the features of fluid migration associated with elizion and infiltration processes will open up new possibilities for predicting hydrocarbon deposits within the Nepa-Botuoba anteclise.


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