«Geology, geophysics and development of oil and gas fields»

Predictive assessment of the seal rocks propagation in sulfate-carbonate deposits of the Oka superhorizon, Orenburg region

UDC: 550.8:553.98(470.56)
DOI: -

Authors:

¹ SamaraNIPIneft, Samara, Russia
² Gazpromneft Group of Companies, Saint Petersburg, Russia
³ Orenburgneft, Orenburg, Russia

Keywords: Visean stage, Oka superhorizon, Volga-Ural oil and gas province, sulfate seal rocks, carbonate reservoirs, risk maps

Annotation:

The Oka superhorizon (the Upper Visean sub-stage of the Lower Carboniferous) of the Volga-Ural oil and gas province includes a series of productive carbonate formations (O₁–O₆), separated by sulfate, sulfate-carbonate and clayey-carbonate seal rocks. From the bottom up to the superhorizon section the proportion of sulfate rocks (anhydrites) in the seal units increases. Analysis of lithological and petrophysical studies of the Oka superhorizon core allowed assessing the reservoir properties of the formations and the quality of the seals. Particular attention is paid to the carbonate-sulfate and sulfate deposits of the intra-shelf lagoon as the most promising seals for screening hydrocarbon deposits. Typing of seals by lithological composition and assessment of their heterogeneity and changes of thickness over the area were performed. Ultimately, based on a series of obtained geological maps, it became possible to rank and map various zones taking into account the risks of a trap formation. Maps give an idea of the main fluid seals distribution in structural-facies zones at the regional level. To assess the territorial distribution of seals in the section of the Mikhailovskiy and Venevskiy horizons, a set of prepared maps was taken into account: seal thickness, lithological type distribution and lithological purity of dense rocks or homogeneity. Maps of the reservoir layers distribution were additionally built. Various maps combination provided mapping zones with an increased risk of traps formation and territories favorable for the probable formation of hydrocarbon deposits. This work can serve as a basis for substantiating promising objects and searching for deposits in already discovered fields and new license areas. To improve and clarify forecasts, it is recommended to combine the presented approach with seismic and other studies.

Bibliography:

1. Otsenka kachestva kollektorov i flyuidouporov v razreze sul’fatno-karbonatnoy tolshchi okskogo nadgorizonta Orenburgskoy oblasti / V.A. Shakirov, A.P. Vilesov, V.N. Kozhin [i dr.] // Geologiya, geofizika i razrabotka neftyanykh i gazovykh mestorozhdeniy. – 2024. – № 4(388). – S. 13–26.

2. Rol’ pokryshek v sokhrannosti zalezhey uglevodorodov v sul’fatno-karbonatnom razreze / T.G. Nemirovich, A.P. Vilesov, Yu.A. Butolina [i dr.] // Neftepromyslovoe delo. – 2015. – № 3. – S. 30–36.

3. Novyy vzglyad na geologicheskoe stroenie slozhno postroennykh okskikh plastov Volgo-Ural’skoy NGP / T.G. Nemirovich, A.P. Vilesov, Yu.A. Butolina, L.S. Starukhin // Geologiya, geofizika i razrabotka neftyanykh i gazovykh mestorozhdeniy. – 2015. – № 1. – S. 4–11.

4. Boyarshinova M.G., Kalina R.I. Litologiya karstovykh otlozheniy razreza verkhnego vize Zalesskoy ploshchadi (severo-zapadnaya chast’ Orenburgskoy oblasti, Rossiya) // Vestnik geonauk. – 2022. – № 331. – S. 3–10. – DOI: 10.19110/geov/2022.7.1

5. Bakirov E.A., Gabrielyants G.A., Khanin A.A. Ekraniruyushchaya sposobnost’ glinistykh pokryshek i ee vliyanie na raspredelenie gazovykh zalezhey (na primere otdel’nykh rayonov Karakumskoy platformy) // Geologiya i razvedka gazovykh i gazokondensatnykh mestorozhdeniy. – 1968. – № 2.

6. Masagutov R.Kh., Kamilov D.U. Usloviya osadkonakopleniya i perspektivy neftenosnosti mikhaylovskikh otlozheniy okskogo nadgorizonta platformennogo Bashkortostana // Vestnik Evraziyskoy nauki. – 2021. – № 5. – T. 13. – S. 1–11.