25th International Meeting on Organic Geochemistry IMOG 2011

P-013
Study on non GC amenable fractions in biodegraded oils of the
Liaohe Basin by negative-ion ESI FT-ICR MS and PY-GC
Yuhong Liao 1 , Quan Shi 2
1 Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China, 2 China
University of Petroleum, Beijing, Beijing, China (corresponding author:liaoyh@gig.ac.cn)
In our research, 7 biodegraded oils extracted from
reservoir cores of two columns of the Liaohe Basin,
NE China, were studied. These tar sand extracts are
of known identical source and similar maturity,
representing a natural sequence of increasing degree
of biodegradation. These bitumens are termed with
the degrees of biodegradation on Peters and
Moldowan scale (abbreviated as PM level). Kim et al.
(2005) showed that biodegradation alters both the
core nuclei and alkyl side chain distributions in neutral
nitrogen and oxygen polar compounds using ESI FT-
ICR-MS. The methods of elemental composition,
δ13C, δ15N, together with ESI FT ICR-MS and Py-
GC, were used to study the influence of
biodegradation on heavy fractions in crude oils of the
Liaohe Basin.
In our research, ESI FT-ICR MS suggested that
relative abundance of O2 species in asphaltene
fraction are no less than in maltene fraction though
asphaltenes were re-precipitated repeatedly,
sonicated and washed by n-alkane repeatedly,
indicating that organic acids may be linked to
functionalities of asphaltene structure by such as Hbonding.
In maltenes fraction, N1 species are
dominated by carbazoles, benzocarbazoles and
dibenzocarbazoles. N1 species decrease much with
biodegradation. NO species decrease significantly
with biodegradation, especially in the range of PM
level 2-4 (Es3 column). In asphaltene fraction, N1
species are dominated by dibenzocarbazoles and N1
compounds with even higher aromaticity. The
distribution of N1 species at various biodegradation
levels is very similar. NO species in asphaltenes show
higher aromaticity than maltenes. NO species also
decrease with biodegradation, but the distribution is
very similar. The more condensed and multiheteroatomic
nitrogen-containing species will likely be
in the asphaltene fraction, and the least condensed
nitrogen species are likely in the resin fraction. N1
and NO species with higher aromaticity and less alkyl
side chains show higher polarity and are likely
precipitated by n-hexane as a part of asphaltene
fraction. The progressive consumption of susceptible
nitrogen species may continually change δ15N values
in biodegradation. Conversely, the δ15N values of the
asphaltenes are fairly constant at PM levels > 3,
suggesting that once the most susceptible nitrogen
species are removed, the remaining species are
relatively stable.
Py-GC can provide structural information of alkyl
side chains of asphaltenes by crack them into small
ones. In the range of PM level 5-8, TOC-normalized
intensity of n-alkanes plus n-alkenes of identical
carbon number produced by quantitative pyrolysis
(PY-GC) of asphaltenes decrease with biodegradation
(Fig. 1), especially at PM level 8. It suggested that
alkyl side chains of asphaltenes are progressively
shortened during biodegradation.
TOC TOC normalized normalized Intensity Intensity
1200
900
600
300
Es 1
0
6 8 10 12 14 16 18 20 22 24 26
Carbon number
L-5 L-6 L-7 L-8
Fig. 1 TOC normalized intensity of n-alkanes plus nalkenes
with identical carbon numbers
Reference:
Rubinstein, I., Spyckerelle, C., Strausz, O.P., 1979.
Pyrolysis of asphaltenes: a source of geochemical
information. Geochimica et Cosmochimica Acta 43, 1-6.
Connan, J., 1984. Biodegradation of crude oils in
reservoirs. In: Brooks, J., Welte, D.H. (Eds.), Advances
in Petroleum Geochemistry I. Academic Press, London,
UK, pp.298–335.
Kim, S., Stanford, L.A., Rodgers, R.P., Marshall, A.G.,
Walters, C.C., Qian, K., Wenger, L.M., Mankiewicz, P.,
2005. Microbial alteration of the acidic and neutral polar
NSO compounds revealed by Fourier transform ion
cyclotron resonance mass spectrometry. Organic
Geochemistry 36, 1117-1134.
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