geochemistry of resins in dispersed organic matter and oils of west siberia

3
664 ISSN 1028-334X, Doklady Earth Sciences, 2008, Vol. 420, No. 4, pp. 664–666. © Pleiades Publishing, Ltd., 2008. Original Russian Text © L.S. Borisova, A.E. Kontorovich, 2008, published in Doklady Akademii Nauk, 2008, Vol. 420, No. 3, pp. 382–384. The composition and structure of petroleum resins have been discussed in many works [1–3 and others]. The genetic geochemistry of resins in dispersed organic matter (OM) and oils is insufficiently studied [4, 5]. This work continues our studies of resin–asphaltene components in oils and dispersed OM carried out at the Siberian Research Institute of Geology, Geophysics, and Raw Mineral Materials and the Institute of Petro- leum Geology and Geophysics. The purpose of these studies is to establish a correlation between the main parameters of resins and the geochemical characteris- tics of West Siberian oils, define peculiar features of oil resins of different genetic phenotypes, and reveal a genetic correlation between source rocks and oils. We analyzed resin samples of West Siberian oils taken from host rocks of different ages (from the Pale- ozoic to the Albian–Cenomanian) and resins of terrige- nous and marine DOM extracted from bitumens in source rocks of West Siberia. The resins were studied by different physical and physicochemical methods: element analysis, spectroscopy in the infrared (IR) and visible spectra, high-resolution NMR spectroscopy, and EPR. According to [6], marine varieties of resins from the DOM are enriched in hydrogen (like kerogen and asphaltene [7]) as compared with the terrigenous vari- eties (9.33 versus 7.09%, respectively) and are charac- terized by higher (H/C) at values (1.39 and 1.08, respec- tively) (Fig. 1), indicating the greater role of aliphatic and cycloaliphatic structures in their chemical compo- sition. The elemental composition of resins from terrig- enous dispersed OM also differs from that of resins from its marine varieties in the higher concentration of heteroatoms (largely on account of oxygen). In resins from the terrigenous dispersed OM, the concentration of 13 C is higher (by 25.3‰ on average) than in resins from marine OM, in which the value varies from –32.5 to –29.4‰. The study of dispersed OM by IR and NMR spec- troscopy confirms the high content of aromatic struc- tures in resins from terrigenous OM (Fig. 1). In these structures, carbon in aromatic rings accounts for more than 50% of its total quantity, less than half of the rings being replaced by aliphatic and cycloaliphatic radicals. In resins of marine OM, 35% of carbon atoms, on aver- age, are aromatic with 45% of them being replaced. According to EPR spectroscopy, resins of marine OM have a superfine structure provided by the tetravalent vanadium in vanadyl porphyrines. The EPR spectrum of resins from terrigenous OM is lacking superfine structures. Thus, the study of resin components from bitumens by different physical and physicochemical methods revealed peculiar features in their compositions and structures depending on their marine or terrestrial origin. Oil resins were studied in tens of deposits in West Siberia. In southern areas of the region, eight resin sam- ples were taken from oils in Middle Jurassic rocks (Yakkun’yakh, Pikhtovoe, Novyi Yutym, and Ust- Tegus fields) located in southern areas. Four resin sam- ples were taken from oils in Paleozoic rocks (Khyl’kin and Srednii Yulzhav fields). In the central part of West Siberia, oil resins were sampled from Lower Jurassic rocks of the Priozernaya and Ur’evsk deposits. The col- lection from the northern and northeastern areas included oil resins from Aptian–Albian (Tagul field) and Cenomanian (Russkaya field) rocks. The analysis of available data revealed a relatively strong correlation between different parameters of oil resins, suggesting that they represent a genetically inte- gral unity. The atomic hydrogen/carbon ratio (H/C at ) represents the most informative parameter of resins. The higher this value, the higher the concentration of resins in oils and the more aliphatic their structure. The more aliphatic the structure of resins, the higher the content of sulfur (R = 0.78) and tetravalent vanadium (R = 0.62) and the lower the concentration of aromatic carbon (R = –0.98) and paramagnetic centers (R = –0.83) in resins. The concentration of paramagnetic centers in Geochemistry of Resins in Dispersed Organic Matter and Oils of West Siberia L. S. Borisova and Academician of the RAS A. E. Kontorovich Received December 11, 2007 DOI: 10.1134/S1028334X08040302 Institute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences, pr. akademika Koptyuga 3, Novosibirsk, 630090 Russia; e-mail: [email protected] GEOCHEMISTRY

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Page 1: Geochemistry of resins in dispersed organic matter and oils of West Siberia

664

ISSN 1028-334X, Doklady Earth Sciences, 2008, Vol. 420, No. 4, pp. 664–666. © Pleiades Publishing, Ltd., 2008.Original Russian Text © L.S. Borisova, A.E. Kontorovich, 2008, published in Doklady Akademii Nauk, 2008, Vol. 420, No. 3, pp. 382–384.

The composition and structure of petroleum resinshave been discussed in many works [1–3 and others].The genetic geochemistry of resins in dispersed organicmatter (OM) and oils is insufficiently studied [4, 5].This work continues our studies of resin–asphaltenecomponents in oils and dispersed OM carried out at theSiberian Research Institute of Geology, Geophysics,and Raw Mineral Materials and the Institute of Petro-leum Geology and Geophysics. The purpose of thesestudies is to establish a correlation between the mainparameters of resins and the geochemical characteris-tics of West Siberian oils, define peculiar features of oilresins of different genetic phenotypes, and reveal agenetic correlation between source rocks and oils.

We analyzed resin samples of West Siberian oilstaken from host rocks of different ages (from the Pale-ozoic to the Albian–Cenomanian) and resins of terrige-nous and marine DOM extracted from bitumens insource rocks of West Siberia. The resins were studiedby different physical and physicochemical methods:element analysis, spectroscopy in the infrared (IR) andvisible spectra, high-resolution NMR spectroscopy,and EPR.

According to [6], marine varieties of resins from theDOM are enriched in hydrogen (like kerogen andasphaltene [7]) as compared with the terrigenous vari-eties (9.33 versus 7.09%, respectively) and are charac-terized by higher (H/C)

at

values (1.39 and 1.08, respec-tively) (Fig. 1), indicating the greater role of aliphaticand cycloaliphatic structures in their chemical compo-sition. The elemental composition of resins from terrig-enous dispersed OM also differs from that of resinsfrom its marine varieties in the higher concentration ofheteroatoms (largely on account of oxygen). In resinsfrom the terrigenous dispersed OM, the concentrationof

13

C is higher (by 25.3‰ on average) than in resins

from marine OM, in which the value varies from –32.5to –29.4‰.

The study of dispersed OM by IR and NMR spec-troscopy confirms the high content of aromatic struc-tures in resins from terrigenous OM (Fig. 1). In thesestructures, carbon in aromatic rings accounts for morethan 50% of its total quantity, less than half of the ringsbeing replaced by aliphatic and cycloaliphatic radicals.In resins of marine OM, 35% of carbon atoms, on aver-age, are aromatic with 45% of them being replaced.According to EPR spectroscopy, resins of marine OMhave a superfine structure provided by the tetravalentvanadium in vanadyl porphyrines. The EPR spectrumof resins from terrigenous OM is lacking superfinestructures.

Thus, the study of resin components from bitumensby different physical and physicochemical methodsrevealed peculiar features in their compositions andstructures depending on their marine or terrestrial origin.

Oil resins were studied in tens of deposits in WestSiberia. In southern areas of the region, eight resin sam-ples were taken from oils in Middle Jurassic rocks(Yakkun’yakh, Pikhtovoe, Novyi Yutym, and Ust-Tegus fields) located in southern areas. Four resin sam-ples were taken from oils in Paleozoic rocks (Khyl’kinand Srednii Yulzhav fields). In the central part of WestSiberia, oil resins were sampled from Lower Jurassicrocks of the Priozernaya and Ur’evsk deposits. The col-lection from the northern and northeastern areasincluded oil resins from Aptian–Albian (Tagul field)and Cenomanian (Russkaya field) rocks.

The analysis of available data revealed a relativelystrong correlation between different parameters of oilresins, suggesting that they represent a genetically inte-gral unity. The atomic hydrogen/carbon ratio (H/C

at

)represents the most informative parameter of resins.The higher this value, the higher the concentration ofresins in oils and the more aliphatic their structure. Themore aliphatic the structure of resins, the higher thecontent of sulfur (

R

= 0.78) and tetravalent vanadium(

R

= 0.62) and the lower the concentration of aromaticcarbon (

R

= –0.98) and paramagnetic centers (

R

= –0.83)in resins. The concentration of paramagnetic centers in

Geochemistry of Resins in Dispersed Organic Matterand Oils of West Siberia

L. S. Borisova and

Academician of the RAS

A. E. Kontorovich

Received December 11, 2007

DOI:

10.1134/S1028334X08040302

Institute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences,pr. akademika Koptyuga 3, Novosibirsk, 630090 Russia;e-mail: [email protected]

GEOCHEMISTRY

Page 2: Geochemistry of resins in dispersed organic matter and oils of West Siberia

DOKLADY EARTH SCIENCES

Vol. 420

No. 4

2008

GEOCHEMISTRY OF RESINS 665

resins correlates, in turn, with the content of aromaticcarbon (

R

= 0.91). The oil density shows a strong cor-relation with practically all the studied parameters ofresins.

The obtained data demonstrate that the composi-tions and structures of resins are closely related to theelemental compositions of oils and structural peculiar-ities of their hydrocarbon constituent. For example,resin components in the examined light oils fromLower Jurassic rocks are characterized by low concen-trations of sulfur, high contents of oxygen, lack ofvanadyl porphyrines, and a high aromaticity degree ofmolecules (according to NMR and IR spectroscopy).The low density of these oils and insignificant contentof sulfur in them are consistent with the obtained dataon resins. These oils likely originate from terrigenousor mixed OM. This is also confirmed by data on biom-arker hydrocarbons: maximum

n

-alkanes in them cor-respond to C

27

, steranes are dominated by C

29

, and thepristine/phytane ratio is >2. It is conceivable that sourcerocks contain significant concentrations of terrigenousOM, in addition to marine.

The oil resins from Paleozoic rocks demonstratecharacteristics close to the parameters observable inLower Jurassic resins: a low sulfur content and lack ofvanadyl porphyrines. Such a composition of oils (inparticular, resinous components) could result from theinfluence of secondary processes (for example, cat-agenesis). According to [8], the catagenetic transforma-tion degree of host sediments is classified as apocat-agenesis.

In terms of the atomic hydrogen/carbon ratio, aro-maticity degree, and concentration of vanadyl porphy-rines and sulfur, as well as contents and ratios of oxy-gen-bearing structures, oil resins from Middle Jurassicrocks are similar to their counterparts from bitumens ofmarine OM [6]. This is consistent with the high density,resin and sulfur contents, and distribution of

n

-alkanesand steranes typical of marine oils [9].

According to gas–liquid chromatography andCHM-MS data, the examined oils from Aptian–Cen-omanian rocks of northeastern West Siberia are biode-graded. It is difficult to classify these oils according totype of primary OM based on both the composition ofresins and the biomarker hydrocarbon parametersbecause steranes are dominated by C

29

, while tricycla-nes are practically missing. All the IR, NMR, and EPRparameters and the elemental composition of resinsfrom biodegraded oils demonstrate values intermediatebetween typical marine and typical terrestrial. Sincenorthern areas were characterized by intense verticalmigration of hydrocarbons, these oils are most likely ofmixed origin. It is conceivable that the influence ofhypergene processes is reflected even in changes ofsome parameters of the heterocyclic components(increase in aromaticity degree and condensation ofmolecular structures).

Thus, the source rock–oil genetic relations arereflected most distinctly in the contents of sulfur, oxy-gen, and porphyrines. In terms of hydrogen concentra-tion and carbon distribution, resins from all the exam-ined oils are closer to their counterparts from marineOM (Fig. 1). This is also clearly evident from the dia-gram demonstrating the elemental composition of res-

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C

α

/

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ar (primary)

(c)

30 40 50 60

C

ar

, %

(b)

1

2

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1.1 1.3 1.5(H/C)

at

(a)

Occurrence frequency

Fig. 1.

Bar charts of compositions and structures of resins:(a) atomic ratio of hydrogen and carbon; (b) content of car-bon in aromatic structures of resins; (c) the degree ofreplacement of aromatic structures by aliphatic compounds.(

1

) Marine OM; (

2

) terrigenous OM; (

3

) oil.

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DOKLADY EARTH SCIENCES

Vol. 420

No. 4

2008

BORISOVA, KONTOROVICH

ins from oils and resins of different genetic types: fieldsof resins from marine and terrigenous OM differ inhydrogen concentrations, while resins of oils from hostrocks of different ages fall into the field of resins frommarine OM (Fig. 2).

Thus, the study of resinous components in WestSiberian oils reveals that they are characterized by

peculiar compositions and properties. Therefore, theycan be used for solving many genetic problems of oilsand interpreting their subsequent geochemical history,including the influence of secondary processes (cat-agenesis and hypergenesis).

REFERENCES

1. S. R. Sergienko, B. A. Taimova, and E. I. Talalaev,

High-Molecular Nonhydrocarbon Oil Compounds: Resinsand Asphalthenes

(Nauka, Moscow, 1979) [in Russian].2. V. F. Kam’yanov, R. S. Aksenov, and V. I. Titov,

Hetero-atomic Oil Components

(Nauka, Novosibirsk, 1983) [inRussian].

3. A. K. Golovko, L. V. Gorbunova, V. F. Kam’yanov, et al.,

Chemical Composition of Oils from West Siberia

(Nauka, Novosibirsk, 1988) [in Russian].4. G. F. Grigor’eva, A. V. Ryl’kov, L. E. Svitnitskikh, et al.,

in

Geochemistry of Oils and Bitumens in Upper Jurassicand Lower Cretaceous Sediments of the Tyumen Region

(ZapSibNIGNI, Tyumen, 1970), pp. 58–143 [in Rus-sian].

5. I. V. Goncharov,

Geochemistry of Oils of West Siberia

(Nedra, Moscow, 1987) [in Russian].6. A. E. Kontorovich, L. S. Borisova, and E. P. Strekhle-

tova, Geokhimiya, No. 6, 853 (1995).7. A. E. Kontorovich and L. S. Borisova, Geokhimiya,

No. 11, 1660 (1994).8. A. N. Fomin, A. E. Kontorovich, and V. O. Krasavchikov,

Geol. Geofiz.

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, 1875 (2001).9. A. E. Kontorovich, K. E. Peters, J. M. Moldovan, et al.,

Geol. Geofiz., No. 10, 3 (1991).

95

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510152025SNO H

C

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2

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Fig. 2.

Ternary diagram of the elemental composition ofresins. (

1

) Terrigenous OM; (

2

) marine OM; (

3

) oil.