25th International Meeting on Organic Geochemistry IMOG 2011

P-270
Aromatic hydrocarbons in oils occurring in Lake Baikal
Galina Pevneva 1 , Natalya Voronetskaya 1 , Anatoly Golovko 1 , Vladimir Kashirtsev 2
1 Institute of Petroleum Chemistry SB RAS, Tomsk, Russian Federation, 2 Institute of Oil-and-Gas Geology
and Geophyisics SB RAS, Novosibirsk, Russian Federation (corresponding author:pevneva@ipc.tsc.ru)
Both geologists and biologists pay great attention
to the investigation of oil shows in Lake Baikal
because of fear of eco-catastrophe [1,2].
Physicochemical characteristics and
compositions of alkyl-aromatic hydrocarbons have
been investigated in an oil film gathered from Lake
Baikal surface and in natural oil show – bitumen taken
from the bottom of the lake at a depth of 869 m. The
samples were taken in 2008 during diving of a deepwater
station ―Mir‖. The samples were preliminary
dehydrated and purified from mechanical
contaminations.
The oil gathered from the surface greatly differ
from a bottom bitumen sample by lower values of
density (886 and 994 kg/m 3 , respectively), molecular
mass (352 a.u.m. and 584 a.u.m.) and pour point
(minus 11 о С and plus + 44 о С). The samples also
differ in element compositions. The oil sample
contains С=85.6 %; Н=13.4 %; N=0.48 % S=0.17 %
and O=0.4 %. The bitumen contains С – 87.5 %; Н –
9.9 %; N – 0.8%; S – 0.1 % and O – 1.8 %. In the oil
the content of hetero-elements is lower than in the
bitumen sample however the oil is more sulfurous.
The amount of resins in the bitumen is 17.3 % and
that of asphaltenes – 6.9 %. In the oil the content of
resins is 2.3 times and that of asphaltene – 5 times
lower as compared with the bitumen.
In both samples saturated hydrocarbons have
maximal concentrations, i.e. 55.2 and 58.0 %. Amount
of aromatic hydrocarbons in the bitumen is lowers as
compared with that in oil. Triaromatic hydrocarbons
predominate among arenes in both samples. In the oil
amount of mono- and biarenes is comparable (8.5
and 8.4 %, respectively). In the bitumen sample the
content of monoarenes is ~ twice lower than that of
biarenes (1.7 and 3.6 %, respectively).
Using chromatography-mass-spectroscopy we
analyzed compositions of alkyl-aromatic
hydrocarbons of benzene (m/z 91, 105, 119, 133),
naphthanene (m/z 128, 142, 156, 170, 184) and
phenanthrene (m/z 178, 192, 206, 220) series in the
both samples. In the oil among alkylbenzenes ortomethyl-substituted
isomers (1,2-MAB) predominate
over meta-isomers (1,3-MAB) and alkylbenzenes with
a chain of normal structure (n-AB) and para-methyl
isomers (1,4-MAB). There are no tetra-substituted
alkylbenzenes in this sample. Homologous series of
n-AB and methylalkylbenzenes consist of the
compounds with a number of carbon atoms ranging
from 12 to 27. Molecular-mass distribution of both n-
AB and MAB is unimodal with a maximum falling on
low-molecular alkylbenzenes С14-С16. In the elution
region of high-molecular alkylbenzenes containing 23-
27 carbon atoms in a molecule one observes a
―naphthenic hump‖ though peaks of alkylbenzenes
are clearly recorded in a chromatogram.
Among alkylnaphthalenes the concentration of
trimethylnaphthalenes is maximal. Such distribution is
typical to the oils occurring in Lower Jurassic deposits
of West Siberia and in Paleozoic deposits of major oiland-gas
bearing basins. Group composition of
alkylphenanthrenes in the oil from Lake Baikal is
similar to that of major oils. In the Baikal oil
dimethylphenanthrenes predominate over methyl- and
trimethylphenanthrenes.
In the bitumen sample alkyl-aromatic
hydrocarbons of benzene, naphthalene and
phenanthrene series were not determined. Probably
fractions of mono-, bi- and triarenes of this sample
mainly contain naphthenoaromatic compounds.
Thus it was shown that oil sample gathered from
the Baikal surface and that of natural oil show -
bitumen, taken from the bottom of the lake, differ in
oily, resin and asphaltene contents as well as in
hydrocarbon composition. In oil aromatic
hydrocarbons of benzene, naphthalene and
phenanthrene series are presented by alkylsubstituted
isomers, whereas in bitumen naphthenosubstituted
compounds predominate.
1. Khlystov O.M., Gorshkov A.G., et al. //Proc. of the
Russian Academy of Sciences. 2007. V.414. № 5.
P.656-659.
2.Kontorovich A.E., Kashirtsev V.A., et al. // Geologia
I Geofizika. 2007.V.48. № 12. P.1346-1356.
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