Features of the transformation of Visean quartz sandstones under the influence of water-oil fluids

Research subject. This article analyses specific features of secondary transformations of quartz grains under the influence of water-oil fluids on the example of the Tulsky and Bobrikovsky oil-saturated quartz sandstones of the Demkinskoye oil deposit in the south-east of Tatarstan.

Materials and methods. The research was carried out using the methods of optical microscopy, x-ray diffraction and electron paramagnetic resonance (EPR).

Results. On the example of the Tulsky and Bobrikovsky oil-saturated Visean quartz sandstones, we analysed the influence of wateroil fluids on rocks and features of the secondary transformations of quartz grains in the Demkinsky oil field in the southeast of Tatarstan Republic. In the oilcharge stage, the spatial redistribution of silica was realized. Quartz grains dissolved in the sole and middle part of the reservoir, precipitating in the form of chalcedony in the top part of the reservoir. The dissolution of quartz grains was promoted by micro defects concentrated on their periphery. The dissolution was triggered by both plastic deformations of minerals at the contacts and an increase in the alkalinity in the pore space up to pH = 9-10. Chalcedony aggregates were formed in the intergranular space of oil-saturated sandstones. Depending on the nucleation point of the siliceous substance and silica concentration in pore fluids, either single spherulitic or agate-type aggregates were formed. According to EPR, the studied chalcedony aggregates have a high content of paramagnetic E'-centres. This was caused by a deficiency of oxygen in the mineral-forming fluid during chalcedony precipitation.

Conclusions. Chalcedony precipitation underwent in acidic conditions, which led to silica-type metasomatism in the top part of the reservoir followed by substitution of muscovite grains by morphological fibrous chalcedony. Metasomatism affected the grains of both detrital muscovite and muscovite present as inclusions inside quartz grains. This process indicates the manifestation of surface and bulk diffusion of silica, affecting all clastic components.

1. Astarkin S.V., Goncharenko O.P., Pimenov M.V. (2013) Sedimentation settings during the Bobrikov time within the southeast of the Russian plate. Izv. Saratov Univ. Nov. Ser. Nauki o Zemle, 13(1), 57-62. (In Russian)

2. Baranov V.A. (2014) Microdeformations of quartz in Carboniferous sandstones of Donbas. Vestn. PNIPU. Geo logiya. Neftegazovoe i Gornoe Delo, 12, 75-86. (In Russian)

3. Kagarmanova E.V., Kotenov E.V., Chibisov A.V. (2014) Features of the design and development of small oil fields in Tatarstan. Problemy i Resheniya: Sbornik Nauch. Tr., 3(8), 166-173. (In Russian)

4. Kopeliovich A.V. (1965) Epigenesis of ancient strata of the southwest of the Russian platform. Tr. GIN AN SSSR, 121, 312 p. (In Russian)

5. Korolev E.A. (2014). Stages of transformation of sandy reservoirs of the Tula-Bobrikov age in erosion cuts in the territory of Tatarstan. Uch. Zap. Kazan. Univ. Ser. Es- testv. Nauki, 156(3), 87-97. (In Russian)

6. Korolev E.A., Nurgalieva N.G., Smelkov V.M., Eskin A.A., Kalcheva A.V. (2016) Lithological and petrophysical characteristics oil-saturated deposits of Bobrikovsky horizon on the southern slope of the South-Tatarian arc. Neftyanoe Khozyaistvo, 10, 17-19. (In Russian)

7. Larochkina I.A., Ganiev R.R., Kapkova T.A. (2009) Development of types of oil deposits in working out bobrikovsky adjournments and mechanism of its development - the base of designing of wells boring. Georesursy, 4(32), 19-21. (In Russian)

8. Sakhibgareev R.S. (1989) Secondary reservoir changes during the formation and destruction of oil deposits. Leningrad, Nedra Publ., 260 p. (In Russian)

9. Simanovich I.M. (1978) Quartz of sandy rocks. Moscow, Nauka Publ., 156 p. (In Russian)

10. Simanovich I.M. (2007) Postsedimentary lithogenesis of terrigenous complexes in folded areas: rock structures and cleavages. Lithol. Polezn. Iskop., (1), 84-92. (In Russian)

11. Simanovich I.M., Golovin D.I., Buyakaite M.I., Vinogradov V.I., Sakharov B.A., Matsapulin V.U., Sokolova A.L., Pokrovskaya E.V. (2004) On the influence of geodynamic factors on the postsedimentary lithogenesis of the Jurassic terrigenous complexes of the Caucasus (southern Dagestan). Lithol. Polezn. Iskop., (6), 638650. (In Russian)

12. Chukin G.D. (2008) Surface chemistry and structure of dispersed silica. Moscow, Paladin Printing House, 172 p. (In Russian)

13. Yapaskurt O.V., Parfenova O.V., Kosorukov V.L., Sukhov A.V. (1999) Genesis and staged transformations of micas and chlorites in different geodynamic conditions of lithogenesis. Vestn. MGU. Ser. 4. Geologiya, (5), 3-12. (In Russian)

14. Yapaskurt O.V., Rostovtseva Yu.V., Karpova E.V. (2003) Postsedimentary lithogenesis of terrigenous complexes and paleotectonics. Litosfera, 1, 39-53. (In Russian)

15. Yulbarisov E.M., Yulbarisov I.M. (2012) Enhanced oil recovery methods should be equal to oil fields quantity. Georesursy, 6(48), 75-79. (In Russian)