Geochemical evidence for petroleum potential of Domanic deposits in the Republic of Tatarstan

UDK: 553.98(470.41)
Key words: Domanic deposits, oil generation potential, maturity, kerogen, organic matter
Authors: R.S. Khisamov (Tatneft PJSC, RF, Almetyevsk), V.G. Bazarevskaya, PhD, T.I. Tarasova, O.V. Mikhailova, S.N. Mikhailov (TatNIPIneft, RF, Bugulma)
Detailed survey of Domanic formations in Tatarstan has been under way since 2012. To date, sufficient amount of data has been obtained and analyzed. The analysis shows that Domanic formations in Tatarstan are presented by domanikites occupying a large starved basin of the Sargaev-Domanik-Mendymskian age and having TOC of 5 – 20 %, and domanikoids being analogous to Upper Frasnian-Tournaisian shallow-water bioherm-carbonate deposits and having TOC of 0.5 – 5%. These deposits occupy the central areas of the Kama-Kinel system of starved downwarps and the total territory of Tatarstan. 
According to data analysis, domanikites are presented by nonuniform interbedding of carbonate-silica rocks with limestones and dolomites. Organic matter varies from very low to high concentrations. But, regardless of high variation range, the majority of the core samples (55%) have organic matter content over 4%. Whatever organic matter content is, domanikites exhibit HI from 300 to 600 mg·HC/g, which is typical of oil generating kerogen, type 2 (sapropelic). Generally, rock maturity is rather low; according to pyrolysis data, Tmax value averages to 425oC, corresponding to protocatagenesis termination zone. Hence, domanikites are at the beginning of the main oil generation phase. However, deposits maturity within the South-Tatar uplift is higher compared to the Melekessk depression, which can obviously be attributed to specific geothermal conditions in this area, as well as to formation of deposits with high sulphur content, which affected rock maturity distribution and the type of kerogen capable of generating early pre-main-phase oils. These oils contain heavy components (resins and asphaltenes) and sulphur. Analysis of Tatarstan oil composition and density supports this idea. 
Domanikoids are presented by carbonates with varying content of organic matter which, in general, is rather low. As compared to domanikites, domanikoids have higher content of humus substance. Rock maturity is low; according to pyrolysis data, Tmax averages to 424oC, which corresponds to protocatagenesis zone. Productivity index (PI) conforms to Tmax values and corresponds to protocatagenesis zone, as well. 
So, both domanikites and domanikoids exhibit good hydrocarbon potential, being at the end of protocatagenesis and at the start of mezocatagenesis processes throughout the entire territory under consideration. However, considering the potential for early pre-main-phase oil generation and presence of confirmed oil accumulations in Domanic facies associated with natural fracture zones, we can conclude that these deposits show good promise for discovering new unconventional oil reservoirs. To produce oil from such reservoirs, optimization of thermal recovery processes, as well as acid and multi-stage fracturing methods is required.
References
1. Postnova E.V., Podgornaya E.V., Merkulov O.I., Navrotskiy O.K., Sozdanie geologo-
geokhimicheskoy modeli s tsel'yu otsenki stepeni perspektivnosti
vyyavlennykh i podgotovlennykh lokal'nykh ob"ektov na osnove programmnogo
produkta firmy Beicip-Franlab (Creation of geological and geochemical
models to assess the degree of prospects of identified and blocked
out local objects on the basis of Beicip-Franlab software product), Saratov:
Publ. of NVNIIGG, 2002, 56 р.
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rezul'tatov issledovaniya kerna (11 obraztsov) s tsel'yu opredeleniya
petrofizicheskikh i geokhimicheskikh svoystv porod (Processing and interpretation
of results of core analysis (11 samples) to determine the petrophysical
and geochemical properties of rocks), Moscow: Publ. of Lomonosov
Moscow State University, 2013, 279 р.
3. Gavrilov S.S., Dakhnova M.V., Panchenko I.V. et al., Provedenie petrofizicheskikh
i geokhimicheskikh issledovaniy kerna (Petrophysical and geochemical
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s tsel'yu vydeleniya perspektvinykh intervalov i vozmozhnykh kollektorov
(The geochemical and petrophysical studies of core samples (Frasnian
stage) of well no. 300 of Tlyanche-Tamakskaya area in order to highlight of
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State University, 2014, 439 р.
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petrofizicheskikh i geokhimicheskikh issledovaniy kerna (Petrophysical
and geochemical core studies),, Moscow: Publ. of VNIGNI, 2015, 120 р.
6. Plotnikova I.N., Morozov V.P. et al., Izuchenie litologo-petrograficheskikh i
geokhimicheskikh svoystv domanikovykh otlozheniy na territorii Romashkisnkogo
mestorozhdeniya (Berezovskaya ploshchad', Aznakaevskaya
ploshchad', Zelenogorskaya ploshchad') (The study of the lithological and
petrographic and geochemical properties of the Domanik sediment on the
Romashkisnkoe field (Berezovskaya area, Aznakaevskaya area, Zelenogorskaya
area)), Kazan': Publ. of KSU, 2015, 244 р.
7. Stupakova A.V., Fadeeva N.P. et al., Litologo-geokhimicheskie issledovaniya
otlozheniy domanikovoy formatsii (semilukskiy gorizont-famen) s
tsel'yu ustanovleniya istochnikov UV v zapadnoy chasti Yuzhno-Tatarskogo
svoda – Bavlinskoe mestorozhdenie (The lithological and geochemical
studies of Domanik formation (Semiluk horizon-Famennian) to determine
the sources of hydrocarbons in the western part of the South-Tatar arch -
Bavlinskoye field), Moscow: Publ. of Lomonosov Moscow State University,
2015, 361 р.
8. Peters K.E., Cassa M.R., Applied source rock geochemistry, In: The petroleum
system – From source to trap: AAPG Memoir 60/edited by Magoon
L.B., Dow W.G., USA, Tulsa: The American Association of Petroleum Geologists,
1994, pp. 93-120.
9. Khristoforova N.N., Khristoforov A.V., Bergemann M.A., Analysis of geothermal
maps and petroleum potential of the deep sediments (on the Republic
Tatarstan example) (In Russ.), Georesursy = Georesourses, 2008, no. 3 (26),
pp. 10–12.
10. Bushnev D.A., Early cretaceous anoxic basin of the Russian plate: Organic
geochemistry (In Russ.), Litologiya i poleznye iskopaemye = Lithology and
Mineral Resources, 2005, no. 1, pp. 25–34.

Detailed survey of Domanic formations in Tatarstan has been under way since 2012. To date, sufficient amount of data has been obtained and analyzed. The analysis shows that Domanic formations in Tatarstan are presented by domanikites occupying a large starved basin of the Sargaev-Domanik-Mendymskian age and having TOC of 5 – 20 %, and domanikoids being analogous to Upper Frasnian-Tournaisian shallow-water bioherm-carbonate deposits and having TOC of 0.5 – 5%. These deposits occupy the central areas of the Kama-Kinel system of starved downwarps and the total territory of Tatarstan. 
According to data analysis, domanikites are presented by nonuniform interbedding of carbonate-silica rocks with limestones and dolomites. Organic matter varies from very low to high concentrations. But, regardless of high variation range, the majority of the core samples (55%) have organic matter content over 4%. Whatever organic matter content is, domanikites exhibit HI from 300 to 600 mg·HC/g, which is typical of oil generating kerogen, type 2 (sapropelic). Generally, rock maturity is rather low; according to pyrolysis data, Tmax value averages to 425oC, corresponding to protocatagenesis termination zone. Hence, domanikites are at the beginning of the main oil generation phase. However, deposits maturity within the South-Tatar uplift is higher compared to the Melekessk depression, which can obviously be attributed to specific geothermal conditions in this area, as well as to formation of deposits with high sulphur content, which affected rock maturity distribution and the type of kerogen capable of generating early pre-main-phase oils. These oils contain heavy components (resins and asphaltenes) and sulphur. Analysis of Tatarstan oil composition and density supports this idea. 
Domanikoids are presented by carbonates with varying content of organic matter which, in general, is rather low. As compared to domanikites, domanikoids have higher content of humus substance. Rock maturity is low; according to pyrolysis data, Tmax averages to 424oC, which corresponds to protocatagenesis zone. Productivity index (PI) conforms to Tmax values and corresponds to protocatagenesis zone, as well. 
So, both domanikites and domanikoids exhibit good hydrocarbon potential, being at the end of protocatagenesis and at the start of mezocatagenesis processes throughout the entire territory under consideration. However, considering the potential for early pre-main-phase oil generation and presence of confirmed oil accumulations in Domanic facies associated with natural fracture zones, we can conclude that these deposits show good promise for discovering new unconventional oil reservoirs. To produce oil from such reservoirs, optimization of thermal recovery processes, as well as acid and multi-stage fracturing methods is required.
References
1. Postnova E.V., Podgornaya E.V., Merkulov O.I., Navrotskiy O.K., Sozdanie geologo-
geokhimicheskoy modeli s tsel'yu otsenki stepeni perspektivnosti
vyyavlennykh i podgotovlennykh lokal'nykh ob"ektov na osnove programmnogo
produkta firmy Beicip-Franlab (Creation of geological and geochemical
models to assess the degree of prospects of identified and blocked
out local objects on the basis of Beicip-Franlab software product), Saratov:
Publ. of NVNIIGG, 2002, 56 р.
2. Bogomolov A.Kh., Kalmykov G.A., Kozlova E.V. et al., Obrabotka i interpretatsiya
rezul'tatov issledovaniya kerna (11 obraztsov) s tsel'yu opredeleniya
petrofizicheskikh i geokhimicheskikh svoystv porod (Processing and interpretation
of results of core analysis (11 samples) to determine the petrophysical
and geochemical properties of rocks), Moscow: Publ. of Lomonosov
Moscow State University, 2013, 279 р.
3. Gavrilov S.S., Dakhnova M.V., Panchenko I.V. et al., Provedenie petrofizicheskikh
i geokhimicheskikh issledovaniy kerna (Petrophysical and geochemical
core studies), Moscow: Publ. of VNIGNI, 2013, 126 р.
4. Stupakova A.V. , Fadeeva N.P. et al., Geokhimicheskie i petrofizicheskie
issledovaniya kerna (franskiy yarus) skv. no. 300 Tlyanchi-tamakskoy ploshchadi
s tsel'yu vydeleniya perspektvinykh intervalov i vozmozhnykh kollektorov
(The geochemical and petrophysical studies of core samples (Frasnian
stage) of well no. 300 of Tlyanche-Tamakskaya area in order to highlight of
prospective collectors and intervals), Moscow: Publ. of Lomonosov Moscow
State University, 2014, 439 р.
5. Fortunatova N.K., Shvets-Teneta-Guriy A.G., Dakhnova M.V. et al., Provedenie
petrofizicheskikh i geokhimicheskikh issledovaniy kerna (Petrophysical
and geochemical core studies),, Moscow: Publ. of VNIGNI, 2015, 120 р.
6. Plotnikova I.N., Morozov V.P. et al., Izuchenie litologo-petrograficheskikh i
geokhimicheskikh svoystv domanikovykh otlozheniy na territorii Romashkisnkogo
mestorozhdeniya (Berezovskaya ploshchad', Aznakaevskaya
ploshchad', Zelenogorskaya ploshchad') (The study of the lithological and
petrographic and geochemical properties of the Domanik sediment on the
Romashkisnkoe field (Berezovskaya area, Aznakaevskaya area, Zelenogorskaya
area)), Kazan': Publ. of KSU, 2015, 244 р.
7. Stupakova A.V., Fadeeva N.P. et al., Litologo-geokhimicheskie issledovaniya
otlozheniy domanikovoy formatsii (semilukskiy gorizont-famen) s
tsel'yu ustanovleniya istochnikov UV v zapadnoy chasti Yuzhno-Tatarskogo
svoda – Bavlinskoe mestorozhdenie (The lithological and geochemical
studies of Domanik formation (Semiluk horizon-Famennian) to determine
the sources of hydrocarbons in the western part of the South-Tatar arch -
Bavlinskoye field), Moscow: Publ. of Lomonosov Moscow State University,
2015, 361 р.
8. Peters K.E., Cassa M.R., Applied source rock geochemistry, In: The petroleum
system – From source to trap: AAPG Memoir 60/edited by Magoon
L.B., Dow W.G., USA, Tulsa: The American Association of Petroleum Geologists,
1994, pp. 93-120.
9. Khristoforova N.N., Khristoforov A.V., Bergemann M.A., Analysis of geothermal
maps and petroleum potential of the deep sediments (on the Republic
Tatarstan example) (In Russ.), Georesursy = Georesourses, 2008, no. 3 (26),
pp. 10–12.
10. Bushnev D.A., Early cretaceous anoxic basin of the Russian plate: Organic
geochemistry (In Russ.), Litologiya i poleznye iskopaemye = Lithology and
Mineral Resources, 2005, no. 1, pp. 25–34.



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