Lithologic-paleogeographic characteristics of the Bobrikovskian sedimentation stage in the Orenburg region

UDK: 553.98 (470.4)
DOI: 10.24887/0028-2448-2017-10-75-79
Key words: Bobrikovskian horizon, lithological composition, sedimentation environments, facies
Authors: S.V. Astarkin, V.V. Коlpakov (KogalymNIPIneft Branch of the LUKOIL-Engineering LLC in Tyumen, RF, Tyumen), О.P. Goncharenko (Saratov State University, RF, Saratov), Yu.А. Pisarenko (Lower Volga Scientific and Research Institute of Geology and Geophysics JSC, RF, Saratov), V.P. Morozov (Kazan (Volga Region) Federal University, RF, Kazan)

Terrigenous beds of the Bobrikivskian horizon are among the principal production facilities in the Orenburg region. Diverse views on the formation environments of the deposits testify to the complex structure of the study object and emphasize the actuality of the current research. 

The paper deals with the structure, composition and formation environments of the Bobrikovskian horizon in the Orenburg region. Complex sedimentological examinations of the core material from the prospect-appraisal and exploratory wells have been made. Formation settings of the Bobrikovskian horizon have been reconstructed, a paleogeographic chart has been developed. Productive strata are peculiar for non-uniform structure, which is mostly controlled by the bed genesis. Aleurite-sandy and clayey rocks were formed either in the marine basin zones with active hydrodynamics of the sedimentation environment (coastal-marine, shallow-water marine facies of the near and the far zones), or in an accumulative alluvial-deltaic plain. At that, the principal sedimentation regulator consisted of the environment itself and the unstable sedimentation processes against the background of the basin general gradual subsidence in the Early Visean. Those fast-acting factors account for the frequent facies conversions of the aleurite-sandy rocks into clayey ones and for the lenticular-discontinuous structure of the strata, considerably complicating exploration and development of the hydrocarbon deposits. 

Peculiarities of the area tectonic structure and development, paleo-relief of the bottom and the evolution character of the sedimentation basin have predestined development of a particular type of the Bobrikovskian horizon section within the specified facies-paleogeographic zones in the southeast of the Volga-Ural anteclise. Promising explorations are associated with the sections represented by alternating sandstones, aleurolites and argillites peculiar for higher contents of sandy material (up to 70%) and confined to the deltaic and coastal-marine facies-paleogeographic zones. Those may result in discoveries of hydrocarbon pools in non-structural and combined traps.

References

1. Aliev M.M., Yarikov G.M., Khachatryan R.O., Kamennougol'nye otlozheniya Volgo-Ural'skoy neftegazonosnoy provintsii (Carboniferous deposits of the Volga-Ural oil and gas province), Moscow: Nedra Publ., 1975, 262 p.

2. Allyuvial'no-del'tovye sistemy paleozoya Nizhnego Povolzh'ya (Alluvial delta systems of the Paleozoic of the Lower Volga region): edited by Babadagly V.A., Saratov: Publ. of Saratov University, 1982, 156 p.

3. Astarkin S.V., Goncharenko O.P., Pimenov M.V., Depositional environment in Bobrikovsky time within the south-east of the Russian plate (In Russ.), Izvestiya Saratovskogo universiteta. Novaya seriya. Seriya nauki o Zemle = Izvestia of Saratov University. New Series. Series: Earth Sciences, 2013, V. 13, no. 1, pp. 57–62.

4. Astarkin S.V., Goncharenko O.P., Pisarenko Yu.A., Morozov V.P., Type sections from the terrigenous Lower Visean oil and gas-bearing complex in the Middle Volga Region (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2016, no. 7, pp. 66–68.

5. Leonov G.V., Pogudin V.N., Erosion structures of the pre-Visean deposit in the Orenburg region (In Russ.), Geologiya nefti i gaza, 1989, no. 12, pp. 10–16.

6. Yatskevich S.V., Vorob'ev V.Ya., Nikitin Yu.I., Paleorivers: it's a myth, a "river-mania" or a result of scientific research (In Russ.), Nedra Povolzh'ya i Prikaspiya, 2011, V. 66, pp. 15–40.

7. Pisarenko Yu.A., Vorob'ev V.Ya. et al., Results of regional geological and geophysical works on territory of south-eastern part of Russian plate and prospects of their further activity (In Russ.), Geologiya nefti i gaza = The journal Oil and Gas Geology, 2011, no. 1, pp. 68–77.

Terrigenous beds of the Bobrikivskian horizon are among the principal production facilities in the Orenburg region. Diverse views on the formation environments of the deposits testify to the complex structure of the study object and emphasize the actuality of the current research. 

The paper deals with the structure, composition and formation environments of the Bobrikovskian horizon in the Orenburg region. Complex sedimentological examinations of the core material from the prospect-appraisal and exploratory wells have been made. Formation settings of the Bobrikovskian horizon have been reconstructed, a paleogeographic chart has been developed. Productive strata are peculiar for non-uniform structure, which is mostly controlled by the bed genesis. Aleurite-sandy and clayey rocks were formed either in the marine basin zones with active hydrodynamics of the sedimentation environment (coastal-marine, shallow-water marine facies of the near and the far zones), or in an accumulative alluvial-deltaic plain. At that, the principal sedimentation regulator consisted of the environment itself and the unstable sedimentation processes against the background of the basin general gradual subsidence in the Early Visean. Those fast-acting factors account for the frequent facies conversions of the aleurite-sandy rocks into clayey ones and for the lenticular-discontinuous structure of the strata, considerably complicating exploration and development of the hydrocarbon deposits. 

Peculiarities of the area tectonic structure and development, paleo-relief of the bottom and the evolution character of the sedimentation basin have predestined development of a particular type of the Bobrikovskian horizon section within the specified facies-paleogeographic zones in the southeast of the Volga-Ural anteclise. Promising explorations are associated with the sections represented by alternating sandstones, aleurolites and argillites peculiar for higher contents of sandy material (up to 70%) and confined to the deltaic and coastal-marine facies-paleogeographic zones. Those may result in discoveries of hydrocarbon pools in non-structural and combined traps.

References

1. Aliev M.M., Yarikov G.M., Khachatryan R.O., Kamennougol'nye otlozheniya Volgo-Ural'skoy neftegazonosnoy provintsii (Carboniferous deposits of the Volga-Ural oil and gas province), Moscow: Nedra Publ., 1975, 262 p.

2. Allyuvial'no-del'tovye sistemy paleozoya Nizhnego Povolzh'ya (Alluvial delta systems of the Paleozoic of the Lower Volga region): edited by Babadagly V.A., Saratov: Publ. of Saratov University, 1982, 156 p.

3. Astarkin S.V., Goncharenko O.P., Pimenov M.V., Depositional environment in Bobrikovsky time within the south-east of the Russian plate (In Russ.), Izvestiya Saratovskogo universiteta. Novaya seriya. Seriya nauki o Zemle = Izvestia of Saratov University. New Series. Series: Earth Sciences, 2013, V. 13, no. 1, pp. 57–62.

4. Astarkin S.V., Goncharenko O.P., Pisarenko Yu.A., Morozov V.P., Type sections from the terrigenous Lower Visean oil and gas-bearing complex in the Middle Volga Region (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2016, no. 7, pp. 66–68.

5. Leonov G.V., Pogudin V.N., Erosion structures of the pre-Visean deposit in the Orenburg region (In Russ.), Geologiya nefti i gaza, 1989, no. 12, pp. 10–16.

6. Yatskevich S.V., Vorob'ev V.Ya., Nikitin Yu.I., Paleorivers: it's a myth, a "river-mania" or a result of scientific research (In Russ.), Nedra Povolzh'ya i Prikaspiya, 2011, V. 66, pp. 15–40.

7. Pisarenko Yu.A., Vorob'ev V.Ya. et al., Results of regional geological and geophysical works on territory of south-eastern part of Russian plate and prospects of their further activity (In Russ.), Geologiya nefti i gaza = The journal Oil and Gas Geology, 2011, no. 1, pp. 68–77.


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