Physicochemical Characteristics and Hydrocarbon Composition
Post on 04-Jun-2018
220 Views
Preview:
Transcript
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
1/12
www.elsevier.com/locate/rgg
The physicochemical characteristics and hydrocarbon compositionof crude oils of the TimanPechora petroliferous basin
A.K. Golovko*, V.F. Kamyanov, V.D. Ogorodnikov
Institute of Petroleum Chemistry, Siberian Branch of the Russian Academy of Sciences, Akademicheskii pr. 4, Tomsk, 634021, Russia
Received 12 April 2011; accepted 23 April 2012
Abstract
The total hydrocarbon composition and average structural-group characteristics of typical Paleozoic crude oils of the TimanPechora
petroliferous basin are described. The hydrocarbon (HC) types of crudes are compared, which were conventionally determined from the
composition of their gasoline fractions, by mass-spectrometric analysis of the HC composition of crudes, and by structural-group analysis of
crudes, based on radiospectrometric data. The analyses have shown the presence of 30 structural types of HCs with up to 43 carbon atoms.
The whole series of members up to C43are specific only for HCs with no more than three rings in the molecule. It has been established that
the carbonate strata in the basin under investigation, independently of the depth of their occurrence and the age of the host deposits, generate
and accumulate heavy high-resin high-sulfur oils rich in alicyclic structures and assigned by HC composition to the naphthenemethane or
even naphthene type. Terrigenous reservoirs here abound in crudes of methanenaphthene type. The contents of sulfur and resinous substances
and the fraction of carbon atoms in alicyclic HC structures decrease as the depth of occurrence of the host deposits grows, thus reflecting the
known gradual process of methanization of petroleum composition.
2012, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.
Keywords: crude; chemical type; hydrocarbons; composition
Introduction
The TimanPechora petroliferous basin is an ancient sedi-
mentary basin with commercial oilfields in Paleozoic deposits
differing strongly in age (from Permian to Ordovician), the
depth of occurrence (100 to 4500 m), and lithologic compo-
sition. At greater depths (to 5600 m), natural-gas fields were
found (Beka and Vysotskii, 1976; Maksimov, 1987; Ostrovskii
et al., 1985).
Earlier analyses showed that the crude oils found in the
basin horizons of different ages are greatly diverse by the mostcrucial compositional and technical parameters: density (4
20=
822975 g/cm3), contents of sulfur (mainly 0.32.0 wt.%),
resinasphaltene substances (RAS) (526 wt.%), and paraffin
(29 wt.%), hydrocarbon (HC) composition, etc. (Bazhenova
et al., 2008; Driatskaya et al., 1972; Golovko et al., 2006a,b;
Guseva and Geiro, 1974; Ostrovskii et al., 1985). Oil-bearing
stratigraphic complexes were discovered within the basin
based on the available geological information and data of field
research and chemical analyses of crudes by methods used in
modern geochemistry of natural HC systems. These methods
include determination of the general physicochemical charac-
teristics and composition of crudes and the contents and
molecular-mass distribution (MMD) of biorelict HCs, includ-
ing normal and isoprenoid alkanes, as well as tetracyclic
(steranes) and pentacyclic (triterpanes) naphthenes. It was
established that the main regional oil resources are localized
in Upper ViseanLower Permian carbonate reservoirs (from
Okian to SakmarianArtinskian ones, C1v3P1ar) and in
MiddleUpper Devonian terrigenous deposits (Givetian andFrasnian Stages, D2gvD3fr
1). The composition parameters
helped to determine the geochemical types of the basin crude
oils.
The modern analytical methods based on results of ra-
diospectrometric and mass-spectral analyses of crudes and
their components permit determination of the average struc-
tural-group (Kamyanov, 1986; Kamyanov and Bolshakov,
1984; Kamyanov et al., 1988) or total (Kamyanov and
Golovko, 2004a) HC composition of crude oil. Both ap-
proaches are proposed for the elaboration of new ways of
chemical classification based on the data on each object as a
whole rather than its relatively small portion (gasoline, alkane,
Russian Geology and Geophysics 53 (2012) 12161227
* Corresponding author.E-mail address: golovko@ipc.tsc.ru (A.K. Golovko)
Available online at www.sciencedirect.com
ed.
1068-7971/$ - see front matterD 201 IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reservV S.. S bol evo2,
http://dx.doi.org/10.1016/j.rgg.2012.09.008
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
2/12
or polycyclane) (Kamyanov et al., 1999; Kamyanov and
Golovko, 2003, 2004c).
We applied these new analytical methods to study 15
representative samples of crude oils from a few deposits of
the TimanPechora Basin. The results of the study are
discussed below.
The objects and methods of investigation
To study the crude oils accumulated in the carbonate
deposits, we used samples taken from the MoscovianSak-
marian reservoirs in the Usa oilfield and from the Lower
Famennian reservoir in the West Tebuk oilfield (Table 1). The
host rocks differ considerably in age and occur in a narrow
depth range, 12501400 m. Crudes were also extracted from
terrigenous reservoirs in the Devonian horizons located at
greatly different depths: from 150200 m in the Yarega pool
to 3100 m in the Usa oilfield and 3450 m in the Kharyaga
oilfield (Table 2).
The crude samples cleaned from water, mineral salts, andmechanical impurities were separated into asphaltenes, resins,
and oils, using the generally accepted techniques (Bogomolov
et al., 1984; Rybak, 1962). Asphaltenes were removed by
Golde hot separation method, with dilution of the crude with
n-hexane (1 : 40 by volume). The deasphaltenized maltene
samples were adsorbed on large-pored activated silica gel and
placed into a Sohxlet apparatus for the successive extraction
of oils with n-hexane and then of resins with a mixture (1:1
by volume) of benzene and ethanol.
The content of paraffin in crude was determined by
gas chromatography (Kristall-2000 chromatograph, 25 m
0.22 mm quartz capillary column, SE-54 stationary phase,
linear temperature growth from 50 to 290 C with a rate of
3 deg/min, n-hexadecane as an internal standard) with a
subsequent summation of the contents of all n-alkanes heavier
than C16 (C17+). The samples of crude petroleums, and
asphaltenes, resins, and oils isolated from them were studiedby structural-group analysis (SGA), using the technique
elaborated at the Institute of Petroleum Chemistry, Tomsk, and
based on the elemental composition, molecular masses of
substances, and the data of proton magnetic resonance (PMR)
spectrometry (Kamyanov and Bolshakov, 1984; Kamyanov
et al., 1988).
The contents of C and H were determined by elemental
analysis of the products, applying the conventional combustion
methods; the content of N was measured in the Pokrovsky
reactor; and the content of S was determined by the double-
combustion method (Klimova, 1975). The molecular masses
of substances were measured by cryometric technique innaphthalene, using Krion device designed at the Institute of
Petroleum Chemistry, Tomsk. The PMR spectra were recorded
on an AVANCE AV-300 spectrometer, using deuterochloro-
form as solvent (to obtain 10% solution of the substance to
be analyzed) and hexamethyl disiloxane as internal standard.
Below, we use the same designations of structural parame-
ters as Kamyanov et al. (1988):
C, H, N, S, and O mark the number of element atoms in
the molecule; Ca, Cn, Cp, C, and C show the number of
Table 1. Physicochemical characteristics of crude oils from carbonate reservoirs
Parameter Measurement
unit
Oilfields Average
Usa West Tebuk
Well
1122 1250 3006 8105 8412 2517 3063
Average depth of occurrence m 1248 1251 1336 1348 1354 1406 1409 1369 1340
Age C2P1s D3fm1
Density at 20 C g/cm3 964.3 959.2 968.7 970.7 971.5 968.3 931.9 954.0 961.0
Viscosity at 20 C mm2/s 5275 5866 5146 5818 8867 6204 4830 7345 5858
Tpour C 16.0 17.0 14.0 15.0 14.5 14.0 20.0 14.0 15.5
Average molecular mass amu 335 327 310 370 315 372 320 335 336
Content of wt.%
oils 70.0 74.4 72.0 73.2 70.3 71.5 80.4 74.9 74.0
resins 21.5 17.9 19.4 18.4 22.1 19.8 12.6 20.1 18.4
asphaltenes 8.5 7.7 8.6 8.4 7.6 8.7 7.0 5.0 7.6
Elemental composition wt.%
C 84.49 84.50 84.28 85.30 85.48 84.99 84.70 85.93 84.82
H 11.80 11.88 11.67 11.63 10.95 11.35 11.65 11.26 11.56
N 0.46 0.61 0.78 0.66 0.64 0.58 0.72 0.37 0.64
S 2.10 2.04 2.10 2.04 1.97 2.07 1.88 0.99 2.03
O 1.15 0.37 1.17 0.37 0.96 1.01 1.05 1.45 0.95
A.K. Golovko et al. / Russian Geology and Geophysics 53 (2012) 12161227 1217
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
3/12
carbon atoms in the aromatic, naphthene, and paraffin molecu-
lar structures, in the position with respect to the heteroa-
tomic groups and aromatic rings, and in the methyl groups
not bound with the latters, respectively; fa, fn, and fp are the
fractions of carbon atoms in the aromatic, naphthene, and
paraffin structures; Kt, Ka, and Knare the total number of ringsand the number of aromatic and naphthene rings in an average
molecule, respectively; mais the average number of structural
blocks in the molecule; and a is the degree of substitution
of peripheral carbon atoms in the aromatic rings.
Similar parameters of the structural molecule blocks are
asterisked.
The obtained data on the distribution of carbon atoms
among aromatic, naphthene, and paraffin structures were used
to establish the hydrocarbon types of crudes by the classifica-
tion of caustobioliths proposed by Kamyanov et al. (1999).
In some cases, the crudes were also classified according to
their contents of normal alkanes and isoprenoids, as wasproposed by Petrov (1984) and Solodkov et al. (1975).
The oil fractions of crudes were examined not only by SGA
on the basis of radiospectrometric data but also by mass
spectrometry. Today this is the most informative method of
analysis of the HC composition of crudes because it includes
data both on the total contents of HCs of different structural
types and on the MMD of all members of each isobaric-ho-
mologous series. In this work we recorded mass spectra of
oils on a MKh-1310 spectrometer at 250 C and 12 eV.
The mass spectra were processed by the graphoanalytical
method including the following stages:
(1) Measurement of the intensities of all spectral lines.
(2) Introduction of isotopic corrections and calculation of
the correct relative intensity of each peak (in fractions of the
total ion current).
(3) Determination of the contents of components with a
particular molecular mass by the summation of the fractions
of compounds with even (Mi) and odd (Mi1) masses.(4) Graphical construction of the dependencies of the above
contents on the number of carbon atoms in the molecule or
on the molecular mass for seven theoretically possible iso-
baric-homologous HC series from Z= 14n 2 to Z= 14n+
10, where n= 0, 1, or 2.
(5) Division of the constructed plots into zones correspond-
ing to members of particular superposed homologous series,
taking into account that the plots summarize HCs of the
following structural types:
seriesZ= 14n 2alkanes (n= 0,Z= 2), alkylnaphthale-
nes (n = 1, Z = 12), benzotricyclanes (n = 1, Z = 12), and
mononaphthenochrysenes (n= 2, Z= 26);
series Z = 14nmonocyclanes (n = 0, Z = 0), mono-
naphthenonaphthalenes (n = 1, Z = 14), benzotetracyclanes
(n = 1, Z = 14), dibenzofluorenes (n = 2, Z = 28), and
perylenes + benzopyrenes (n= 2, Z= 28);
seriesZ= 14n+ 2bicyclanes (n= 0, Z= 2), naphthobi-
cyclanes (n= 1, Z= 16), alkylfluorenes (n= 1, Z= 16), and
alkylpicenes (n= 2, Z= 30);
seriesZ= 14n+ 4tricyclanes (n= 0, Z= 4), naphthotri-
cyclanes (n= 1,Z= 18), mononaphthenofluorenes (n= 1,Z=
18), and alkylphenanthrenes (n = 1, Z= 18);
series Z = 14n + 6alkylbenzenes (n = 0, Z = 6),
tetracyclanes (n= 0,Z= 6), dinaphthenofluorenes (n= 1, Z=
20), and mononaphthenophenanthrenes (n= 1, Z= 20);
Table 2. Physicochemical characteristics of crude oils from terrigenous reservoirs
Parameter Measurement
unit
Oilfields
Yarega* Upper Omra Lower Omra Dzher Usa Kharyaga
1 2 89 190 2 7 1099
Average depth of occurrence m
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
4/12
series Z = 14n + 8benzomonocyclanes (n = 0, Z = 8),
pentacyclanes (n= 0, Z= 8), dinaphthenophenanthrenes (n=
1, Z= 22), benzofluorenes (n= 1, Z= 22), and alkylpyrenes
(n= 1, Z= 22)
series Z = 14n + 10benzobicyclanes (n = 0, Z = 10),
mononaphthenobenzofluorenes (n= 1,Z= 24), mononaphthe-
nopyrenes (n = 1, Z = 24), and alkylchrysenes (n = 1, Z =
24).Zones corresponding to fragmentary ions were rejected.
To perform the most difficult operation, division of the
plots, we generalized all our and literature data (Kamyanov
et al., 1982; Peters and Moldowan, 1993; Petrov, 1984; etc.)
on the MMD of HCs of different types and have drawn the
main conclusions given below, which must be taken into
account for the successful operation.
In crudes of any HC type, aliphatic HCs (except for
isoprenanes) and those with only one or two rings in the
molecule (mono- and bicyclanes, alkylbenzenes, mononaph-
thenobenzenes, and, sometimes, alkylfluorenes) form wide
monotonous, usually unimodal series with the similar positionsof the most intensive peaks. On the MMD lines of these HCs,
there are episodic small local peaks of members with the
number of carbon atoms multiple of five or one less, which
might be due to the presence of biosynthetic compounds with
the isoprenoid structure of carbon skeletons. Naphthene and
aromatic rings in the molecules of tetra- and pentacyclic
compounds are condensed in the order specific for biologic
steroids and triterpenoids. These compounds form narrower
series, beginning with the simplest theoretically possible
members (C17 and C21, respectively) and ending with mem-
bers no heavier than C35. Such are the series of tetra- and
pentacyclanes, benzotri- and benzotetracyclanes, naphthobi-
and naphthotricyclanes, and mono- and dinaphthenophenan-
threnes.
Hydrocarbons with condensed polyarene cores in the
molecules (alkylphenanthrenes, derivates of pyrene, picene,
and benzo- and dibenzofluorenes) are present in crudes as
narrow unimodal series of few lower members.
In the cases when crudes and their oil fractions were
analyzed by gas chromatography to determine the contents of
n-alkanes and isoprenanes, the total contents of alkanes found
by mass-spectrometric analysis (Z = 2) were additionally
subdivided into fractions of HCs of these structural types and
other isoalkanes.
This technique permitted us to determine the contents ofHCs of 30 isobaric-homologous series in crudes and their oily
parts.
Results and discussion
Oil fractions are the main component of all the described
crudes. They amount to 7080 wt.% of crudes localized in the
SakmarianMoscovian carbonate horizons (C2P1s) of the Usa
oilfield and in the Lower Famennian horizon (D3fm1) of the
West Tebuk oilfield (Table 1). These are heavy (420=
960970 g/cm3), highly viscous (v204200 mm2/s) low-par-
affin (pour point is 14 C) crudes, which points to a low
content of solid hydrocarbons (paraffin). They are S-rich
(~2 wt.% S) and therefore highly resinous (1822 wt.% resins
and 79 wt.% asphaltenes). All these crudes are similar in
elemental composition (wt.%): C84.585.4, H1112, N
0.50.8, S1.92.1, and O0.41.0.
The crudes from the West Tebuk and Usa (well 8412)
oilfields differ from the other studied crudes in higherviscosity. This is due to a domination of naphthenes over
aliphatic HCs in their oil fractions, which serve as dispersion
media in polydispersed crudes. The Usa crude from well 3063
is of lower density because of the lower content of resins.
The crudes extracted from UpperMiddle Devonian ter-
rigenous reservoirs are much more diverse by the depths of
occurrence and physicochemical characteristics (Table 2). We
analyzed crude samples from the Yarega oilfield, localized at
such a shallow depth (150200 m) that it became possible to
extract them not by well but by pit recovery.
The crudes extracted from depths of >3000 m in the Usa
and Kharyaga oilfields are specific by a wide range of theirdensities, 830950 g/cm3, and molecular masses, 300450
atomic mass units (amu).
The crudes extracted from the Dzher and Usa pools are
the sulfur-richest (~1.6 wt.%). The crudes from the Yarega
pool are medium-sulfur (up to 1 wt.% S), and those from the
Upper Omra and Lower Omra oilfields are low-sulfur (0.36
0.38 wt.%). The most deep-seated Kharyaga crude is the
sulfur-poorest (0.1 wt.%).
The resin content of these crudes is correlated with the
sulfur content. The Yarega and Dzher crudes are rich in
resin-asphaltene substances (RAS) (>20 wt.%). The Upper
Omra, Lower Omra, and Usa crudes contain 815 wt.% RAS,
and the Kharyaga crude is the resin-poorest (3.7 wt.% RAS).
Tables 3 and 4 present results of SGA of the oil (concen-
trated HC) fractions of crudes. The objects are grouped
according to their localization in the carbonate or terrigenous
host rocks.
Since most of the molecules of heteroorganic components
of crudes have only one nitrogen and one sulfur atoms and
one or two oxygen atoms, HCs amount to no less than
6070 wt.% of the oils.
The calculated average contents of aromatic rings (struc-
tural units or blocks ma) in the molecules of oils are omitted
from the tables because they are
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
5/12
atoms in naphthene and paraffin structures in the oils of the
Usa crudes vary from 38 to 65 and from 19 to 46%,
respectively.
The HC molecules have two or three ((Ks)av = 2.38)
saturated cycles. Thus, no less than 38% of the molecules have
at least three naphthene rings, i.e., are polycyclane structures
or their dehydroaromatized analogs. The low value of C(2.02.6) indicates that the aromatic rings are localized at the
edges of hybrid naphthene-aromatic cores of the molecules.
The aliphatic fragments in HC molecules of the Usa crudes
usually have 812 (on the average, 9.4) carbon atoms. Atoms
C (3.34.0) enter the methyl substituents of naphthene rings
and the terminal methyl groups of aliphatic chains. This
indicates that the long alkyl fragments including up to 1213
carbon atoms are present in the oil molecules from crudes
localized at a depth of 1250 m (wells 1122 and 1250).
The Usa crudes show no tendency to the enrichment with
alkanes and depletion with naphthenes (methanization of
crudes) with depth. In the depth range 12501350 m, there is,
on the contrary, a significant increase in the fraction of
naphthene carbon and a decrease in the fraction of paraffin
carbon, so that the fp/fndecreases from 1.29 to 0.29 here and
again increases to 0.78 in the most deep-seated crude sample.
That is, the HC type of crude oil transforms with depth, first
Table 3. Physicochemical characteristics and average structural parameters of oil components of crudes from carbonate reservoirs
Parameter Measurement
unit
Oilfields Average*
Usa West Tebuk
1122 1250 3006 8105 8412 2517 3063
Fraction in crude % 70.0 76.4 72.0 73.2 70.3 71.5 80.4 74.9 73.6
Average molecular mass amu 345 295 335 365 327 360 315 332 335Elemental composition wt.%
C 85.05 85.18 85.30 85.05 86.00 85.28 85.22 86.00 85.17
H 11.92 12.22 12.00 11.88 11.26 11.75 12.27 12.46 11.98
N 0.47 0.30 0.70 0.51 0.50 0.56 0.55 0.20 0.51
S 1.75 1.98 1.86 1.90 1.98 1.95 1.57 0.99 1.84
O 0.81 0.32 0.52 0.40 0.26 0.52 0.39 0.35 0.49
Average number of atoms in molecule
C 24.5 20.9 23.7 25.9 23.4 25.5 22.3 23.8 23.7
Ca 3.0 2.9 4.0 4.1 3.9 4.3 3.5 4.0 3.9
Cn 9.3 5.7 10.1 12.0 15.1 13.2 10.5 13.9 10.4
Cp 12.2 12.3 9.6 9.8 4.4 8.0 8.3 5.9 9.4
C 2.5 2.2 2.4 2.6 2.3 2.6 2.0 2.6 2.4
C 3.7 3.3 3.8 3.9 3.5 4.0 3.3 3.6 3.6
H 40.8 35.8 39.9 43.0 36.5 41.8 38.3 41.4 39.9
N 0.12 0.05 0.14 0.14 0.12 0.14 0.12 0.05 0.13
S 0.19 0.18 0.19 0.22 0.20 0.24 0.15 0.10 0.19
O 0.17 0.06 0.11 0.09 0.05 0.12 0.08 0.07 0.11
z= 2C H 8.2 6.0 7.5 8.8 10.3 9.2 6.3 6.2 7.5
100z/C 33.5 28.7 31.6 34.0 44.0 36.1 28.3 26.1 31.6
Fraction of C atoms %
fa 16.4 17.1 17.0 15.8 16.6 16.7 15.8 16.6 16.5 fn 38.0 37.6 42.6 46.5 64.6 51.7 47.2 58.2 44.0
fp 45.6 45.3 40.4 37.7 18.8 31.6 37.0 25.2 39.5
fp/fn 1.20 1.20 0.95 0.81 0.29 0.61 0.78 0.43 0.90
Ring composition
Kt 2.98 2.81 3.19 3.66 5.14 3.93 3.19 4.02 3.16
Ka 0.80 0.79 0.79 0.84 0.73 0.84 0.70 0.66 0.78
Kn 2.18 2.02 2.40 2.82 4.41 3.09 2.49 3.36 2.38
Hydrocarbon type M-N M-N N-M N-M N N-M N-M N N-M
* The sample from well 8412 and West Tebuk crude sample are ignored.
1220 A.K. Golovko et al. / Russian Geology and Geophysics 53 (2012) 12161227
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
6/12
from methanenaphthene into naphthenemethane and even
naphthene and then again into naphthenemethane (according
to the terminology introduced by Dobryanskii (1948)).
The HCs of crude from well 8412 are the most enriched
in naphthene structures: Their fnvalue reaches 64.6%, and fpis as low as 18.8%. According to the SGA results, these
molecules contain (Kn)av = 4.4 naphthene rings. Obviously,
tetra- and pentacyclic compounds are dominated among them.
In this case, the hopanes/steranes ratio must be ~1.5. Note that
similar ratios were earlier established in other crudes from the
same petroliferous complex (Bazhenova et al., 2008).
Aliphatic HCs are scarce in this naphthene crude. They
have, on the average, Cp= 4.4, with 3.5 of which being atoms
of terminal methyl groups. Thus, the alkyl substituents in their
molecules are, most often, one ethyl and a few methyl groups.
The HCs of naphthene crude from the Lower Famennian
horizon of the West Tebuk oilfield have a similar structural-
group composition. On the average, their molecules consist of
24 carbon atoms; 1/3 of the molecules lack aromatic rings
(Ka= 0.66). Naphthenes are also mainly polycyclanes (Kn =
3.66), but steranes and pentacyclic triterpanes amount to no
more than 1/3 of them. Paraffin fragments comprise 25% of
Table 4. Physicochemical characteristics and average structural parameters of oil components of crudes from terrigenous reservoirs
Parameter Measurement
unit
Oilfields
Yarega* Upper Omra Lower Omra Dzher Usa Kharyaga
1 2 89 190 2 7 1099
Fraction in crude % 76.6 68.7 91.6 89.1 75.6 93.7 96.3
Average molecular mass amu 338 390 342 350 320 315 298
Elemental composition wt.%
C 86.33 85.89 85.76 86.60 85.31 86.00 85.95
H 11.66 11.92 13.31 12.52 12.24 12.88 13.54
N 0.10 0.04 0.45 0.18 0.46 0.18 0.17
S 1.04 0.79 0.38 0.36 1.64 1.57 0.11
O 0.09 0.16 0.10 0.34 0.17 0.44 0.23
Average number of atoms in molecule
C 24.0 27.9 24.4 25.3 21.1 22.4 21.3
Ca 3.0 3.9 2.6 3.3 1.6 3.7 2.7
Cn 9.1 10.4 8.1 9.7 8.0 7.1 6.7 Cp 11.9 13.6 10.2 12.3 11.5 11.6 11.9
C 1.8 1.9 1.6 1.9 1.9 2.6 0.5
C 3.8 4.9 4.3 4.6 3.9 3.1 3.0
H 41.4 48.7 45.2 43.5 38.8 38.6 39.7
N 0.02 0.04 0.11 0.05 0.10 0.12 0.01
S 0.11 0.10 0.07 0.04 0.15 0.15 0.09
O 0.02 0.09 0.02 0.07 0.07 0.08 0.02
z= 2C H 6.6 7.1 3.6 7.1 3.4 6.2 2.9
100z/C 27.5 25.4 14.8 28.1 16.1 27.7 13.6
Fraction of C atoms %
fa 12.4 14.1 12.6 13.2 7.6 16.5 12.7
fn 38.0 37.3 38.6 38.2 37.9 31.6 31.5
fp 49.6 48.6 48.8 48.6 54.5 51.9 53.8
fp/fn 1.31 1.30 1.26 1.27 1.52 1.64 1.77
Ring composition
Kt 2.68 2.62 1.80 1.68 1.65 1.86 1.61
Ka 0.53 0.79 0.32 0.26 0.27 0.65 0.45
Kn 2.15 1.83 1.48 1.42 1.38 1.21 1.16
Hydrocarbon type M-N M-N M-N M-N M-N M-N M-N
* Samples were taken from oil pits.
A.K. Golovko et al. / Russian Geology and Geophysics 53 (2012) 12161227 1221
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
7/12
all carbon atoms; on the average, 3.6 of 5.9 atoms (~60%) in
the molecule are carbon atoms of methyl groups, i.e., long
alkyl chains are virtually absent.
The oil components of the crudes from the terrigenous
horizons of the studied pools also differ significantly in many
structural parameters.
Judging from the number of S, N, and O atoms in the
average molecule, the oils from the Dzher and Usa crudeshave up to 30% admixtures of heteroorganic compounds,
including 15 mol.% sulfur-containing and 1012 mol.%
nitrogen-containing ones. The oils from the other crudes have
no more than 20 mol.% nonhydrocarbon admixtures, including
10 mol.% sulfur-containing compounds.
The average molecular mass of oils in the crudes from
terrigenous horizons varies from 300 to 390 amu. Correspond-
ingly, the number of carbon atoms in the molecules varies, on
the average, from 21 to 28; 1214% of them form aromatic
rings. The fraction of aromatic carbon is somewhat higher (up
to 16.5%) in the oils of the Devonian Usa crude and is almost
twice lower (7.6%) in the oils of the Dzher crude.The low average proton deficit of molecules,z= 2C H =
67 (both absolute value and that reduced to 100 carbon atoms
(100z/C) for excluding the influence of molecular mass)
evidences that aromatic HCs in the oils are mainly mono-
arenes.
The main distinctive feature of the studied oils as compared
with HCs from carbonate reservoir crudes is the greater
amount of paraffin and the smaller amount of naphthene
structures. Paraffin structures make up 4955% of all carbon
atoms in the molecules of all studied crudes. Naphthene rings
amount to 31.5% of all carbon atoms in the oils from the Usa
and Kharyaga crudes and 3739% in the rest samples.This abundance of carbon atoms determined the small sizes
of alicyclic fragments of the molecules. Bicyclanes are the
most abundant naphthenes in the Yarega crudes (Kn =
1.82.2). In the rest crude oil samples, the main naphthenes
are monocyclanes (Kn< 1.5). They amount to 8085% of all
naphthenes in the oils from the Usa and Kharyaga crudes.
It is obvious that all studied crudes from terrigenous
reservoirs are of methanenaphthene type. The average size
of naphthene fragments of oil molecules (Kn) monotonously
decreases and the ratio of the fractions of paraffins and
naphthenes (fp/fn) significantly increases as the depth of the
host-rock occurrence grows, i.e., methanization of crudetakes place, which was not observed for the crude in carbonate
rocks. This change in the HC composition of crude with depth
might be either due to a partial differentiation of HCs during
their migration from the oil-generating aluminosilicate
(clayey) rock (Kamyanov and Golovko, 2004a,b) or due to a
catagenetic destruction of high-molecular crude components,
which is catalytically intensified by the present clay minerals.
Thus, the crudes of the TimanPechora petroliferous basin,
especially those in carbonate reservoirs, are rich in sulfur
compounds, which significantly hamper a mass-spectral analy-
sis of their HC composition and can cause a great error of
results if their content is high. Therefore, these crudes have
been poorly studied by the high-efficiency mass-spectrometric
method.
Nevertheless, we performed a mass-spectral analysis of
low-S (0.360.38%) oils from the crudes from the Upper Omra
and Lower Omra oilfields and of oil components (~1% S) of
the crudes from carbonate rocks. Components of these oils
contain, on the average, no more than 0.1 sulfur atom
(Tables 3 and 4); admixtures of sulfur compounds amount to10 mol.%. The results of the performed analyses are sum-
marized in Table 5.
The data obtained show that alkanes are predominant in
the crude from the Upper Omra oilfield, whereas the crudes
from the Lower Omra and, particularly, West Tebuk oilfields
are composed mainly of naphthenes. Moreover, alkanes are
scarcer than aromatic HCs in the West Tebuk crude.
A half (5054%) of all naphthenes in the studied crudes
are monocyclanes, bicyclanes are scarcer (3238%), and tetra-
and, especially, pentacyclanes are minor (
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
8/12
Table 5. Group hydrocarbon composition of studied crude oils (wt.%)
Hydrocarbons Oilfields
Upper Omra Lower Omra West Tebuk
Alkanes 35.610 26.915 14.589
Monocyclanes 17.110 21.878 18.496
Bicyclanes 12.150 13.064 13.976
Tricyclanes 3.310 5.269 4.167
Tetracyclanes 0.186 0.171 0.351
Pentacyclanes 0.081 0.116 0.167
Naphthenes 32.830 40.498 37.157
Alkylbenzenes 11.240 7.742 7.772
Benzomonocyclanes 7.556 5.915 7.152
Benzobicyclanes 2.495 3.079 3.463
Benzotricyclanes 0.619 0.335 0.397
Benzotetracyclanes 0.182 0.391 0.527
Monoarenes 22.09 17.461 19.310
Alkylnaphthalenes 0.725 0064 0.171Naphthomonocyclanes 0.176 0.409 0.196
Naphthobicyclanes 0.081 0.249 0.372
Naphthotricyclanes 0.131 0.257 0.205
Naphthalenes 1.118 0.979 0.943
Alkylfluorenes 0.377 0.126 0.300
Mononaphthenofluorenes 0.104 0.161 0.110
Dinaphthenofluorenes 0.035 0.054 0.048
Fluorenes 0.139 0.341 0.458
Biarenes 1.257 1.320 1.402
Alkylphenanthrenes 0.071 0.252 0.072
Mononaphthenophenanthrenes 0.071 0.067 0.082
Dinaphthenophenanthrenes 0.019 0.084 0.041
Phenanthrenes 0.161 0.403 0.195
Alkylbenzofluorenes 0.070 0.112 0.035
Naphthenobenzofluorenes 0.019 0.017 0.024
Benzofluorenes 0.089 0.129 0.059
Triarenes 0.250 0.632 0.254
Alkylpyrenes 0.030 0.079 0.031
Naphthenopyrenes 0.019 0.026 0.000
Pyrenes 0.049 0.105 0.031
Alkylchrysenes 0.033 0.027 0.047
Naphthenochrysenes 0.092 0.216 0.085
Chrysenes 0.125 0.243 0.132
Dibenzofluorenes 0.123 0.154 0.080
Tetraarenes 0.197 0.502 0.243
Perylenes + benzopyrenes 0.095 0.291 0.122
Picenes 0.014 0.060 0.084
Pentaarenes 0.109 0.351 0.206
Arenes 23.06 20.166 21.417
Total identified 91.500 87.579 73.164
Nonidentified 0.099 0.521 1.736
Total 91.600 88.100 74.900
A.K. Golovko et al. / Russian Geology and Geophysics 53 (2012) 12161227 1223
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
9/12
ied crudes are narrower and include compounds C17C35(Figs. 1, c, eand 2, a). They are dominated by C25C30, with
C27, C29, or C30being in the maximum contents. The MMD
patterns of these HCs are generally similar to those of
crude-oil steranes (Petrov, 1984). Most likely, these HCs are
actually the main tetracyclanes in the studied crudes.
The homologous series of pentacyclanes and their dehy-
droaromatized derivates (benzotetracyclanes, naphthotricycla-
nes, dinaphthenophenanthrenes) in the studied crudes begin
with C21and end with C35or C36. The MMD patterns of these
HCs show maxima for C26C30, with C29 or C30 being
predominant. This suggests that pentacyclic triterpanes and
Fig. 1. Molecular-mass distribution of saturated and monoaromatic hydrocarbons in the Lower Omra crude oil. a, Alkanes; b, c, cyclanes; d, e, monoarenes. 1, alkanes,
2, isoprenanes; 3, other isoalkanes; 4, monocyclanes; 5, bicyclanes; 6, tricyclanes; 7, tetracyclanes; 8, pentacyclanes; 9, alkylbenzenes; 10, benzomonocyclanes;
11, benzobicyclanes; 12, benzotricyclanes; 13, benzotetracyclanes.
1224 A.K. Golovko et al. / Russian Geology and Geophysics 53 (2012) 12161227
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
10/12
their partly dehydrogenized analogs are the most abundant
among the homologues.
Biarenes with fluorene fragments in the crudes are alkyl,
mononaphthene, and dinaphthene derivates with up to 20, 23,
and 26 carbon atoms in the molecule, respectively.
Triarenes are phenanthrene, anthracene, and benzofluorene
derivates containing up to five condensed aromatic and
naphthene rings in the molecule.
It is impossible to differentiate the series of phenanthrenes
and anthracenes by mass spectrometry; therefore, we present
Fig. 2. Molecular-mass distribution of bi-, tri-, and polyarenes in the Lower Omra crude oil. a, Biarenes; b, fluorenes; c, triarenes; d, benzofluorenes; e,f, tetra- and
pentaarenes, respectively. 1, alkylnaphthalenes; 2, mononaphthenonaphthalenes; 3, dinaphthenonaphthalenes; 4, trinaphthenonaphthalenes; 5, alkylfluorenes;
6, mononaphthenofluorenes; 7, dinaphthenofluorenes; 8, alkyl (Ph + A); 9, mononaphthene (Ph + A); 10, dinaphthene (Ph + A); 11, alkylbenzofluorenes;
12, mononaphthenobenzofluorenes; 13, alkylpyrenes; 14, mononaphthonepyrenes; 15, alkylchrysenes; 16, mononaphthenocrysenes; 17, perylenes; 18, dibenzofluo-
renes; 19, picenes.
A.K. Golovko et al. / Russian Geology and Geophysics 53 (2012) 12161227 1225
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
11/12
the total contents of these compounds, Ph + A (Fig. 2). TheseHCs in the crudes show a narrow unimodal (with a C16 peak)
MMD ending with C20C21.
Benzofluorenes and their naphthene derivates in the studied
crudes are represented only by compounds with no more than
four carbon atoms in substituents, with their total content not
exceeding 0.05 wt.%.
Tetracycloaromatic HCs in the studied crudes are alkyl-
and mononaphthene derivates of pyrene and chrysene and
fluorene benzologuesdibenzo- and/or naphthofluorenes. Tet-
raarenes are dominated by chrysene derivates, up to C28inclusive.
Pentaaromatic HCs are minor in the crudes and arerepresented by picenes and perylenes, with the latter being
predominant.
The experimental MMD of HCs of different types in the
crudes of the TimanPechora Basin agrees with the regularities
derived from literature data and used to fulfill stage 5 of
graphoanalytical mass spectra processing.
Summarizing the contents of C7C11 (boiling points 80
200 C) determined from mass spectra, it is possible to
estimate a tentative group composition of the gasoline frag-
ment of each crude, i.e., to perform its typification following
Dobryanskiis (1948) criteria. Calculations showed (Table 6)
that the Upper Omra and Lower Omra crudes must be assigned
to the methane-naphthene type (1 < M:N < 2) according to
gasoline composition, and the West Tebuk one, to the
naphthene type (M:N < 0.5). These mass-spectrometric data
agree with the above results of SGA based on radiospectromet-
ric data.
The Upper Omra and West Tebuk crudes should be
assigned to the same types according to their classification by
the HC composition of the crude as a whole. Using the data
from Table 4, we calculated the M:N values for the sum of
HCs in the two crudes, 1.08 and 0.39, respectively. The results
of typification of the Lower Omra crude by both methods are
different: It is a methane-naphthene crude (M:N = 1.47)
according to its gasoline portion and a naphthene crude
(M:N = 0.66) according to the full set of its HCs. The sameHC types follow from the ratio of the fractions of carbon
atoms in the aliphatic and naphthene fragments of all compo-
nents of the Lower Omra and West Tebuk crudes (fp/fn= 1.17
and 0.40, respectively, Table 4).
Conclusions
Thus, the obtained chemical data clearly show that the
Paleozoic carbonate strata in the TimanPechora Basin, inde-
pendently of their depth of occurrence and age, generate and
accumulate heavy high-resin high-sulfur crudes rich in alicy-clic HCs, which are assigned to the naphthene-methane or
naphthene type by Dobryanskiis (1948) classification.
Terrigenous reservoirs abound in methane-naphthene
crudes. The contents of sulfur and resinous substances and the
fraction of carbon atoms in the alicyclic structures of the HC
molecules of these crudes decrease as the depth of occurrence
of the host deposits grows, thus reflecting the gradual
methanization of crude.
A specific feature of the crude-oil HCs is a predominance
of compounds with one or two naphthene and/or aromatic
rings and long aliphatic substituents in the molecules. The
main components of the studied crudes are alkylmonocyclanes(among naphthenes) and alkylbenzenes (among arenes). These
HCs show a broad, up to C43, mainly unimodal molecular-
mass distribution with the similar positions of peaks. The
MMD of HCs with more than two rings in the molecule is
much narrower and usually includes only a few lower
members of each homologous series.
The kind of junction of the rings in the molecules of
polycyclic HCs suggests their genetic relations with biosyn-
thesized steranes and triterpanes.
All these structural peculiarities of HCs are responsible for
the very high fractions of carbon atoms in aliphatic structures,
even in crudes rich in cyclic compounds.
Table 6. Group hydrocarbon composition of gasoline components C7C11 (wt.%) of studied crude oils
Hydrocarbons Oilfields
Upper Omra Lower Omra West Tebuk
Alkanes 41.48 55.24 25.20
Monocyclanes 19.66 28.60 39.50
Bicyclanes 10.06 9.06 22.60
Naphthenes 29.72 37.66 62.10
Alkylbenzenes 21.14 4.34 6.44
Benzomonocyclanes 7.38 2.69 5.71
Monoarenes 28.52 7.03 12.15
Alkylnaphthalenes 0.29 0.56 0.55
Arenes 28.81 7.59 12.70
Total C7C11 (wt.% of oil) 28.00 26.65 13.38
M:N 1.08 1.47 0.41
1226 A.K. Golovko et al. / Russian Geology and Geophysics 53 (2012) 12161227
8/14/2019 Physicochemical Characteristics and Hydrocarbon Composition
12/12
Thus, the composite multibed terrigenous-sedimentary car-
bonate strata of the studied petroliferous basin show the same
regularities of change in HC composition with depth as those
established earlier in other basins.
References
Bazhenova, T.K., Shimanskii, V.K., Vasileva, V.F., Shapiro, A.I., Yakovleva
(Gembitskaya), L.A., Klimova, L.I., 2008. Organic Geochemistry of the
TimanPechora Basin [in Russian]. VNIGRI, St. Petersburg.
Beka, K., Vysotskii, I.V., 1976. Oil and Gas Geology [in Russian]. Nedra,
Moscow.
Bogomolov, A.I., Temyanko, M.B., Khotyntseva, L.I. (Eds.), 1984. Modern
Methods of Oil Analysis [in Russian]. Nedra, Leningrad.
Dobryanskii, A.F., 1948. Oil Geochemistry [in Russian]. Gostoptekhizdat,
Leningrad.
Driatskaya, Z.V., Mkhchiyan, M.A., Zhmykhova, N.M. (Eds.), 1972. The Oils
of the USSR [in Russian]. Khimiya, Moscow, Vol. 3.
Golovko, A.K., Gorbunova, L.V., Kamyanov, V.F., 2006a. The group
hydrocarbon composition and typification of Devonian oils of the Komi
Republic (from mass spectrometry data), in: Natural Bitumens and Heavy
Oils [in Russian]. Nedra, St. Petersburg, pp. 6478.
Golovko, A.K., Golovko, Yu.A., Gorbunova, L.V., Pevneva, G.S., Kamya-
nov, V.F., 2006b. High-molecular components of Devonian oils of the
TimanPechora province, in: Natural Bitumens and Heavy Oils [in
Russian]. Nedra, St. Petersburg, pp. 7989.
Guseva, A.N., Geiro, S.S., 1974. Geochemical types of oils of the Timan
Pechora Basin. Izvestiya Akad. Nauk. Ser. Geol., No. 8, 105114.
Kamyanov, V.F., 1986. The modern potentialities of a structure-group
analysis of high-boiling oil fractions. Radiospectroscopy as an alternative
of the common n-d-M analysis, in: Study of Oils and Oil Products [in
Russian]. TsNIITENeftekhim, Moscow, pp. 6772.
Kamyanov, V.F., Bolshakov, G.F., 1984. Determination of structural
parameters in a structure-group analysis of oil components. Neftekhimiya
24 (4), 450459.
Kamyanov, V.F., Golovko, A.K., 2003. A new approach to a chemical
typification of oils, in: Oil and Gas Chemistry [in Russian]. Izd. IOA SO
RAN, Tomsk, pp. 9193.
Kamyanov, V.F., Golovko, A.K., 2004a. Biodegradation is not the only way
for the formation of naphthene oils in the Earths interior, in: New Ideas
in Oil and Gas Geology and Geochemisty [in Russian]. GEOS, Moscow,
pp. 223225.
Kamyanov, V.F., Golovko, A.K., 2004b. Formation of naphthene oils in the
Earths interior, in: New Ideas in Oil and Gas Geology and Geochemisty
[in Russian]. GEOS, Moscow, pp. 225229.
Kamyanov, V.F., Golovko, A.K., 2004c. The total hydrocarbon composition
of oils according to recent data, in: New Ideas in Oil and Gas Geology
and Geochemisty [in Russian]. GEOS, Moscow, pp. 230231.
Kamyanov, V.F., Golovko, A.K., Kurakolova, E.A., Korobitsina, L.L., 1982.
High-Boiling Aromatic Hydrocarbons of Oils [in Russian]. Izd. Tomskogo
Filiala SO AN SSSR, Tomsk.
Kamyanov, V.F., Filimonova, T.A., Gorbunova, L.V., Lebedev, A.K.,
Sivirilov, P.P., 1988. Oil resins and asphaltenes, in: The Chemical
Composition of West Siberian Oils [in Russian]. Nauka, Novosibirsk,
pp. 177269.
Kamyanov, V.F., Gorbunova, L.V., Ogorodnikov, V.D., 1999. A new
approach to the classification of caustobioliths. Neftekhimiya 39 (2),
134143.
Klimova, V.A., 1975. The Main Micromethods of Analysis of Organic
Compounds [in Russian]. Khimiya, Moscow.
Maksimov, S.P. (Ed.), 1987. Oil and Gas Deposits of the USSR. A
Reference-Book, Book 1: The European Part of the USSR [in Russian].
Nedra, Moscow.
Ostrovskii, M.I., Botneva, T.A., Pankina, R.G., Shulova, N.S., Kholodi-
lov, V.A., 1985. The composition of oil and formation of its pools in the
OrdovicianLower Devonian deposits of the Pechora syneclise. Sovet-
skaya Geologiya, No. 4, 3539.
Peters, K.E., Moldowan, J.M., 1993. Biomarker Guide. Englewood Cliffs,
New Jersey, Prentice Hall.
Petrov, Al.A., 1984. Oil Hydrocarbons [in Russian]. Nauka, Moscow.
Rybak, B.M., 1962. Analysis of Oil and Oil Products [in Russian]. Gostop-
tekhizdat, Moscow.
Solodkov, V.K., Dragunskaya, V.S., Kamyanov, V.F., 1975. Classification
of oils. Izv. AN TurkmenSSR. Ser. Fiz.-Tekh., Khim. i Geol. Nauk, No. 1,6779.
Editorial responsibility:V.A. Kashirtsev
A.K. Golovko et al. / Russian Geology and Geophysics 53 (2012) 12161227 1227
top related