Mikhailovsky deposits of the Okskian suprahorizon: a new oil-bearing horizon of the Bym-Kungur depression
Key words: oil, deposit, thin rock section, layer, formation, limestone, anhydrite, dolomite, X-ray fluorescence analysis, reservoir, overlying seal, prospects for oil and gas potential
Authors: R.Kh. Masagutov (Academy of Sciences of the Republic of Bashkortostan, RF, Ufa), J.U. Komilov (RN-BashNIPIneft LLC, RF, Ufa), E.A. Krylova (RN-BashNIPIneft LLC, RF, Ufa), O.B. Dyakonova (RN-BashNIPIneft LLC, RF, Ufa)
The discovery of a new oil-bearing formation in the area of the conventional contact between the Mikhailovsky horizon and the Okskian suprahorizon’s Venevsky horizon at Sukhoyazskoye oilfield in the southern part of the East European platform’s Bym-Kungur depression has revealed the need to perform a material composition study, as well as to clarify its stratigraphy and enclosing rocks. The results of the lithologic and faunistic studies carried out jointly with well logging data is being research for the first time in this article. The uppermost layer of anhydrite in the transition zone, clearly visible in the well logs, is called the “upper anhydrite” log marker. It was specified the location of the border between the above mentioned horizons based on anhydrite formation replacement with limestones. The anhydrite formation clearly outlining the top of the Mikhailovsky horizon in well logs is called the “upper anhydrite” benchmark. Together with the underlying anhydrite and dolomite formations, it forms a 10-12-meter rock unit, under which a 4-6.5-meter С1mh limestone productive formation is. Voids of productive layer are represented by small open pores and interform caverns formed as the result of cementing material re-crystallization and desalination, more seldom – by intraform ones formed due to desalination of bioclasts. The deterioration of the reservoir properties is due to micrite filling the intraform and interform voids, as well as sulfate that basically fills the intraform voids. The discovery of favorable conditions for the formation of oil deposits in the Mykhailovsky horizon of Sukhoyazskoye oilfield allows giving a positive evaluation for the oil-and-gas-bearing capacity of the remaining part of the Bym-Kungur depression territory, including the boundaries of Perm and Sverdlovsk regions. Provided the presence of the evaporite facie in the Mikhailovsky horizon rock section is confirmed, other tectonic regions of the platform Bashkortostan territory might also be promising in terms of discovering new deposits in the Mikhailovsky horizon.
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