Lithological and petrophysical characteristics of reservoirs and seals of the Kashirskian sequence in the west of Bashkortostan

UDK: 552.578
DOI: 10.24887/0028-2448-2022-3-26-29
Key words: Kashirskian sequence, carbonate reservoirs, seal-rock, dolomite
Authors: R.V. Mirnov (RN-BashNIPIneft LLC, RF, Ufa), V.N. Minkaev (Bashneft PJSOC, RF, Ufa), I.I. Yagfarov (Bashneft-Dobycha LLC, RF, Ufa)

Kashirskian sequence deposits of the Moscow stage are promising for replenishing the resource base of the Volga-Ural oil and gas province in conditions of depletion of the basic horizons oil reserves. In the Kashirskian sequence, 8 elementary cyclites are distinguished. These cycites have a similar lithological structure and contain signs subaeral erosion at the top. The cyclites are composed of the following lithological types of rocks: clayey mudstones (1), spongolitic siliceous limestones and silicites (2), organic-rich laminated wackestones (3), bioclastic wackestones-packstones (4), bioturbated packstones (5), foraminiferal grainstones (6), polydetritic grainstones (7), laminated bioclastic packstones (8), microcrystalline massive dolomites (9), microcrystalline laminated dolomites (10) and microcrystalline patterned dolomites (11). The main reservoirs are represented by microcrystalline dolomites with high porosity and relatively low permeability and foraminiferal grainstones, similar in properties to terrigenous reservoirs. The C2ks4 reservoir in the lower part of the Kashirskian sequence is composed of foraminiferal grainstones. It is covered by the seal of clayey limestones lithotype (1). The C2ks1 reservoir layer in the top of the Kashirskian sequence is composed of microcrystalline dolomites. The seal includes of polydetritic grainstones and laminated bioclastic packstones with sulfate inclusions. The middle part of the Kashirskian sequence is characterized by a complex interbedding of dolomite and limestone reservoirs with different filtration-volumetric properties and low-permeability rocks (possible seals). The described structural features of the Kashirskian sequence must be taken into account when calculating reserves, as well as when designing horizontal wells and hydraulic fracturing.


1. Kirillov A.I., Akhmatdinov F.N., Lozin E.V. et al., Estimation of the efficiency of oil displacement by water from the reservoir rocks of the middle carboniferous fields of Bashkortostan (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2009, no. 11, pp. 96-99.

2. Khisamov R.S., Khazipov R.G., Bazarevskaya V.G. et al., Studying the structure of void space of complex carbonate rocks of the Kashirskian horizon using electric microscanning technique (In Russ.), Geologiya nefti i gaza, 2014, no. 3, pp. 47–53.

3. Mirnov R.V., Sedimentological cyclicity and lithological features of the Kashirskian sequence in the northwestern Bashkortostan (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2020, no. 7, pp. 79-81, DOI 10.24887/0028-2448-2020-7-79-81.

4. Choquette P.W., Pray L.C, Geologic nomenclature and classification of porosity in sedimentary carbonates, AAPG Bulletin, 1975, V. 54, pp. 207–250, DOI:10.1306/5D25C98B-16C1-11D7-8645000102C1865D

5. Kirkham A., Patterned dolomites: microbial origins and clues to vanished evaporates in the Arab Formation, Upper Jurassic, Arabian Gulf, Geological Society, London, Special Publication, 2004, V. 235, pp. 301–308, DOI:10.1144/GSL.SP.2004.235.01.12

To buy the complete text of article (a format - PDF) or to read the material which is in open access only the authorized visitors of the website can. .

Mobile applications

Read our magazine on mobile devices

Загрузить в Google play