Paleokarst and associated post-sedimentary processes: example of a well in Yurubcheno-Tokhomsky oil and gas accumulation zone
Vasileva K.Y. Ershova V.B. Mikhailova K.Yu. Tikhonova K.A. Kolesov V.A. Prokofev V.Y. Bugrova I.Y.
2025All-Russian Research Geological Oil Institute (VNIGNI)
Geologiya Nefti i Gaza
2025#2025Issue 4137 - 150 pp.
The authors present a detailed lithological description of the Yurubchensky Formation, Riphean, that occur below the surface of pre-Vendian unconformity (south-west of the Siberian Platform, Baikitsky anteclise, Yurubcheno-Tokhomsky area of oil and gas accumulation). The studied rocks have undergone different post-sedimentation transformations, namely: recrystallization, silicification, desalinisation, dedolomitisation, formation of stylolite seams and cracks, filling voids with authigenous quartz and dolomite. A paragenetic diagram of post-sedimentary changes was created for the investigated section interval, and their relationship with the main stages of the Baikitsky anteclise tectonic evolution was determined. Recrystallization, stylolitization, and, possibly, silicification are among the processes related to the stages of sedimentation and basin subsidence. Crack formation and filling with authigenous minerals are attributed to the orogeny stage. Loss of void space with formation of tight, virtually impermeable rock matrix is associated with subsidence and folding stages. The remaining rock porosity (1–2 %) is interpreted as resulting from the partial preservation of small intercrystalline voids. The formation of the void space, later filled with hydrocarbons, occurred under near-surface erosion conditions, during which intensive dolomite dissolution caused the formation of intercrystalline and intracrystalline voids and cracks. The presented paragenetic diagram show that, within the studied interval of the section, the brecciated zones of karst are the most favorable for retaining reservoir quality.
cathode-ray luminescence , dolomite , karst , post-sedimentation alterations , Riphean , void space changes
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St. Petersburg State University, 7/9 Universitetskaya nab., Saint Petersburg, 199034, Russian Federation
Geological Institute of Russian Academy of Sciences, 7, per. Pyzhyovskiy, Moscow, 119017, Russian Federation
RN-KrasnoyarskNIPIneft, 65D, ul. 9 maya, Krasnoyarsk, 660098, Russian Federation
Institute of Geology and Development of Fossil Fuels, 25/1 ul. Vavilova, Moscow, 109472, Russian Federation
LLP Asian Scientific and Technical Center, Astana, Kazakhstan
Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry Russian Academy of Sciences, 35, per. Staromonetny, Moscow, 119017, Russian Federation
St. Petersburg State University
Geological Institute of Russian Academy of Sciences
RN-KrasnoyarskNIPIneft
Institute of Geology and Development of Fossil Fuels
LLP Asian Scientific and Technical Center
Institute of Geology of Ore Deposits
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