Srednebotuobinskoye field (Siberian Platform) case study: tectonic history and water-oil contact considerations
Key words: Nepsko-Botuobinskaya anteclise, Botuobinsky horizon, oil-water contact, tectonics, paleo-accumulation, dissolution
Authors: M.V. Osipova (TNNC LLC, RF, Tyumen)
The work describes the causes of existence of the assumed tilted oilwater contact (OWC) of Botuobinsky horison to update its position in a poorly-drilled part of the field. The paleo-tectonic analysis answers the questions regarding the field structure and its evolution and was performed by the author in the present work in order to define the time of trap formation and accumulation. The paleo-tectonic analysis revealed that at the time of dissolution of Charskaya Formation salts in the eastern part of the field, there existed a paleo-accumulation corresponding to the modern zone of the maximum oil-saturated thickness. Applying the salt level of Charskaya Formation for paleo-tectonic reconstructions is based on the hypothesis that specified nominal surface, controlled by the basis of underwater revetment, had the sub-horizontal character in a process of forming. Afterwards, forming of modern boundaries of Srednebotuobinskiy uplift, took place at the end of the Paleozoic- in the beginning of the Mezozoic. As a result, water-oil contact became tilted. Aligning of OWC was interrupted by the bottom level of high viscosity oxygenated oil. It is proved by the close correlation relationship between the modern structural points of OWC and salt level of Charskaya Formation within the paleo-dome. Apparently, new lots of hydrocarbons were received in the structural trap after formation of modern structural plan of Srednebotuobinskiy uplift. As a result, gas cap was formed and oil rim area was extended. Extension of oil rim area in subsequent stages of accumulation formation can be proved by zero correlation between modern points of OWC and salt level outside the paleo- dome.
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