Assessment of the quality of reservoirs and fluid seals in the section of sulfate-carbonate strata of the Oka super-horizon of the Orenburg region
UDC: 550.98(470.56)
DOI: -
Authors:
SHAKIROV VLADISLAV A.
1,
VILESOV ALEXANDER P.2,
KOZHIN VLADIMIR N.1,
DEMIN SERGEY V.1,
FEDORENKO NIKOLAY V.1,
ABASHKIN ALEXEY YU.1,
EZHIKOVA MARIA M.1,
SOBOLEV VIKTOR I.3,
CHERNOV SERGEY A.3
1 SamaraNIPIneft LLC, Samara, Russia
2 Gazprom neft company group, Saint-Petersburg, Russia
3 Orenburgneft JSC, Orenburg, Russia
Keywords: Oka super-horizon, Lower Carboniferous, sulfate-carbonate deposits, seal rocks, reservoir rocks, petrophysical properties, Orenburg region
Annotation:
The sulfate-carbonate oil and gas complex of the Oka super-horizon in the Orenburg region is a promising object for prospecting oil deposits in fields and newly acquired areas. In order to further study the Oka interval, a comprehensive analysis of a large volume of standard laboratory lithological and petro-physical studies of cores from prospecting and exploration wells was carried out. Based on the results of the analysis, three main lithological types were identified that participate in the structure of the fluid-confining rocks of the Oka super-horizon: anhydrites, sulfate-carbonate rocks and predominantly carbonate rocks. Based on the material composition in the productive strata of the Oka super-horizon, three main lithological types of reservoir rocks have been identified: 1) dolomites; 2) sulfated dolomites; 3) sulfated limestones. Based on the structure of the pore space, reservoir rocks are divided into three groups: fractured-cavernous-porous, cavernous-porous and fractured. During the Oka time, the general trend in the Volga-Ural apicratonic paleobasin was the progressive isolation of intra-platform shallow waters in a hot arid climate, complicated by periodic fluctuations of relative sea level. In the Oka complex there observed a natural increase of the proportion of dolomites and anhydrites from bottom to top along the section. Dolomites are secondary by their genesis, formed as a result of primary limestones metasomatosis. All these features contributed to the formation of a complex evaporite-carbonate Oka natural reservoir with alternation in the section of reservoir units and seals of different properties.
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