Directory UMM :Data Elmu:jurnal:O:Organic Geochemistry:Vol31.Issue12.Dec2000:

Organic Geochemistry 31 (2000) 1509±1523
www.elsevier.nl/locate/orggeochem

Biodegradation and migrational fractionation of oils from
the Eastern Carpathians, Poland
Irena Matyasik a,*, Anna Steczko a, R. Paul Philp b
a

Geology and Geochemistry Department, Oil and Gas Institute, 31-503 Cracow, ul Lubicz 25a, Poland
b
School of Geology and Geophysics, University of OklahomaÐNorman, OK 73019, USA

Abstract
Nineteen oil samples from Silesian Unit of the eastern Carpathian Overthrust have been characterised geochemically
in order to determine the causes of compositional di€erences among them and elucidating the processes responsible for
their di€erences. Some of analysed crude oils have undergone post-emplacement alteration in the reservoir such as
biodegradation and evaporative fractionation. This explains much of the chemical and physical properties variability
across individual ®elds from one tectonic unit. Geochemical correlation based on biomarker distributions showed a
close relationship between all oils (included biodegraded oils). However, data based on the whole oil GC analysis of
selected oils suggest that the process of evaporative fractionation may change the composition of lower molecular
weight hydrocarbons of the oils in this region. This paper outlines the probable mechanisms for oil mixing in the region

and describes how this can lead to observable lateral di€erences in the composition of oils. # 2000 Published by
Elsevier Science Ltd.
Keywords: Biodegradation; Biomarkers; Carpathian Overthrust; Evaporative fractionation; Lower weight hydrocarbons

1. Introduction
The results described in this study will centre on the
geochemical characterisation of oils from the Outer
Carpathian region of Poland which has been a major
petroleum province for over one hundred years. The
Outer Carpathians consist of several major tectonic
units, involving Cretaceous and Paleogene ¯ysch. From
north to south, namely from the external to the more
internal zones, the Polish Outer Carpathian ¯ysch comprises the following units: Stebnik, Skole, Sub-Silesian,
Silesian, Dukla, Magura. These units exhibit strong lateral
facies and thickness changes which were induced by
di€erentiation of the basin ¯oor into cordilleras during
successive compressional episodes, culminating in the
Laramide inversion episode. In the Polish part of the
Carpathian, the main oil ®elds were discovered in both
the Paleogene and Cretaceous ¯ysch. Moreover, they

also contain the source rocks, especially in the early

* Corresponding author.
E-mail address: matyasik@igng.krakow.pl (I. Matyasik).

Oligocene Menilite Shales and in the Albo-Aptian Spas
of the Lower Cretaceous as well in the Upper Cretaceous
Lower Istebna Beds. The Menilite Formation contains
the best potential source-rocks (ten Haven et al., 1993;
Bessereau et al., 1996; Koster et al., 1998a,b). Several
early Cretaceous shales also represent potential, though
less proli®c, source-rocks. The Spas shales are restricted
to the Skole Unit. In the Skole basin, maturation levels
of both the Spas and the Menilite Beds show evidence of
depth-related evolution and reach values corresponding
to the beginning of the ``oil-window'' at depths of about
4000 m (Koltun et al., 1995). In the Silesian basin, Early
Cretaceous strata were located within the oil-window
and Menilite shales might have entered the ``oil-window''
in the deepest parts of the basin (Bessereau et al., 1996).

Previous studies on characterisation of oils from this
region have shown that the oils can be divided into two
main families (ten Haven et al., 1993). The ®rst oil family,
represented by only one sample, has an isotopically light
signature, abundant C29 steranes, and lacks, in contrast
to the second family, characteristic biomarkers such as
oleanane. The second oil family comprises all other oil
samples from the foredeep, as well allochthon, between

0146-6380/00/$ - see front matter # 2000 Published by Elsevier Science Ltd.
PII: S0146-6380(00)00103-0

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I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523

which no signi®cant di€erences could be observed. This
family has an isotopically heavier signature and is characterised by the presence of oleanane, 28,30-dinor-hopane,
and in some oils C25 isoprenoid alkane (HBI) and several
additional biomarkers characteristic of terrigenous

input. Based on sulphur contents and relative abundance
of these biomarkers, the second family was divided into
four subfamilies.
In this study, we describe the geochemical analysis that
were completed on samples from Silesian Unit-Potok
Fold area, in order to reveal similarities and distinctions
among oils from di€erent tectonic blocks. Particular
attention was paid to post-generative alteration processes
on crude oil composition.

2. Samples
Nineteen oil samples were collected from separate
tectonic blocks belonging to the Silesian Unit of the
eastern Carpathian Overthrust. Ten samples were collected in the central area Jaszczew and Potok-Turaszowka
Fields (Moderowka-6; Gaz-11; Maksymilan-2,-3;
Witold-1,-2,-3; Potok-19; Ewa-7,-13), ®ve samples were
taken from western Roztoki-Sobniow Fields (Polmin-7,9; Sobniow-27A,-29; Roztoki-37) and only four from
eastern Kroscienko and Trzesniow Fields (Poznan-11;
Mac Allan-3; Kronen-41 and Trzesniow-10) (Fig. 1a
and b). In the western area, small amounts of gas is

associated with the oil. All the oil- and gas-®elds in the
Carpathians are found in the structural traps, usually
anticlinal folds, which are frequently bounded by faults,
thrust and decollement planes (Karnkowski and Ozimkowski, 1999). The detailed Upper Cretaceous±Tertiary
(Oligocene) lithostratigraphic column for Moderowka-6
well is shown in Fig. 2, considered to be lithologically
representative of the Potok Fold area. The Lower
Istebna beds may be suggested as a potential source
rocks for oils accumulated in upper horizons of this
area. For the characterisation of the oils a multiparameter geochemical approach was applied including
determination of bulk and physical properties of the oils
(gravity, sulphur content, viscosity), as well as whole oil
GC (18 samples, excluding oil from Mac Allan well),
GC of saturated hydrocarbon fractions and GC±MS of
saturated hydrocarbons.

3. Experimental procedures
Whole oil gas chromatography was performed on a
Rtx-1 fused silica capillary column (105 m length, 0.32 mm
i.d., 0.50 mm ®lm thickness) installed in a Fisons GC-800.

The conditions of the GC temperature programme were:
isothermal at 35oC for 10 min, programmed at 3 C/min
to 240 C then at 1 C/min to 300 C and held at the ®nal

temperature for 20 min. Approximately 1 ml of crude oil
was injected without prior preparation and carbon disulphide was used as a solvent.
The asphaltenes were removed from the crude oils by
precipitation from n-hexane. The deasphaltened oils were
fractionated by silica/alumina column chromatography
into saturate, aromatic and polar fractions by elution with
n-hexane, toluene/n-hexane (3:1, v/v) dichloromethane/
methanol (1:1, v/v) respectively. The fractions were analysed by GC and combined gas chromatography-mass
spectrometry on a Fisons quadrupole mass spectrometer
equipped with DB5 fused silica capillary column (60
m0.32 mm0.25 mm) with helium as carrier gas. The
GC temperature program was initially held at 60 C for
2 min, then increased at 4 C/min to a ®nal temperature
of 310 C, which was held for 15 min. Samples were
analysed in the full scan mode, scanning from 50 to 550
amu.

4. Results and discussion
Bulk geochemical data for the oils are given in Table
1. The gravity of oils range from 793.6 for unaltered oils
to 902.6 g/cm3 for oils which have undergone alteration
in reservoir. Sulphur contents of the oils range from
0.02 to 0.34% and are proportional to oil gravity. These
sulphur content variations may be related to alteration
processes such as biodegradation. Oils recognised as
having experienced biodegradation are found in reservoirs
shallower than 750 m in Ciezkowice Sands, from the
central and the eastern area of Potok Fold. The Ciezkowice Sands possess meteoric water input trough faults
to carry dissolved oxygen and micro-organisms into the
reservoirs resulting in biodegradation (Bessereau at al.,
1996). Bacteria introduced into an oil pool with oxygenrich meteoric waters, apparently utilise this dissolved
oxygen and metabolise preferentially certain types of
hydrocarbons. Under anaerobic condition, the oxygen
supply of bacteria is probably derived from dissolved
sulphate ions. The di€erent e€ects of biodegradation on
the molecular composition of crude oils are relatively

well known (Volkman et al., 1984; Peters and Moldowan,
1993; van Aarssen, 1999). Our studies have indicated
that the more extensively biodegraded oils (Po-11, MA-3,
K-41 ) are found in Kroscienko ®eld and among them
the oil from Po-11 is the most altered; absence of the
C15+n-alkanes and isoalkanes. Asphaltene contents are
low and range from 0.4 to 1.7%. Maltene fractions are
dominated by saturated compound especially in SobniowRoztoki ®eld with Sat/Aro ratios in the range 3.3±5.8
and HC/NSO in the range 8.3±20.0 in this reservoir.
These ratios seem to have depth dependence (Fig. 3)
excluding two samples from the Roztoki-Sobniow ®eld
(R-37, P-9). It is due to deeper sedimentary burial of the
Istebna beds in Silesian basin during the generation time.

I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523

Fig. 1. (a) Map showing major Outer Carpathian ¯ysch units; (b) location of study ®elds in the Potok Fold.

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I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523

Fig. 2. Stratigraphic column of the well Moderowka-6.

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I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523
Table 1
Bulk parameters and compositions of oils from Potok Fold ®elds
Code

P-7
S-27A
S-29
P-9
R-37
Mo-6
G-11

M-2
M-3
W-1
W-3
W-6
P-19
E-7
E-13
Po-11
MA-3
K-41
T-10
a

Well

Polmin-7
SobnioÂw-27A
SobnioÂw-29
Polmin-9

Roztoki-37
ModeroÂwka-6
Gaz-11
Maksymilian-2
Maksymilian-3
Witold-1
Witold-3
Witold-6
Potok-19
Ewa-7
Ewa-13
PoznanÂ
Mac Allan-3
Kronen-41
Trzes nioÂw-10

Depth
(m)

1304±1300
2295±2285
2240±2203
1230±1222.6
1523±1500
1776±1753
1133±1123
1108±1105
1138±1077
742±738
708±620
728±720
1750±1712
341±331.5
272±239
445±354
415.6±375.6
524±521.5
268±263.7

Lithiostratigraphy

II Ciezkowice Sand.
Istebna Beds
Istebna Beds
Istebna Beds
Lower Istebna Beds
Lower Istebna Beds
Upper Istebna Beds
Upper Istebna Beds
Ciezkowice Sand.
II Ciezkowice Sand.
II Ciezkowice Sand.
II Ciezkowice Sand.
Upper Istebna Beds
Ciezkowice Sand.
I Ciezkowice Sand.
I Ciezkowice Sand.
I Ciezkowice Sand.
II Ciezkowice Sand.
Intermenilite Sand.

Gravitya Viscositya Sulphur Compound
(kg/m3) (mm2/s)
(%)
groups (%)

839.6
840.1
845.3
840.2
793.6
873.2
822.1
828.1
824.9
826.5
824.3
828.1
842.5
861.4
860.3
902.6
880.3
898.2
844.2

77.6
10.95
11.47
6.94
2.00
18.11
3.76
4.84
3.57
3.26
3.14
3.33
18.69
8.00
2.27
24.00
12.99
20.32
8.10

0.20
0.08
0.09
0.09
0.02
0.18
0.05
0.08
0.06
0.15
0.16
0.11
0.05
0.33
0.32
0.34
0.30
0.19
0.34

Sat/Aro HC/NSO

Sat

Aro Resin Asph

68.4
75.9
74.5
80.8
79.3
72.3
72.2
73.8
64.3
52.1
53.9
55.2
75.5
44.2
42.6
36.6
49.3
59.2
64.3

20.8
18.5
18.5
13.9
15.6
20.0
21.7
19.3
27.2
30.7
27.9
28.0
17.4
32.4
37.5
40.6
30.8
26.6
23.5

10.2
4.9
6.3
4.8
4.4
6.6
5.4
6.0
7.6
15.8
17.1
15.8
6.7
22.1
18.4
21.1
18.2
13.0
11.0

0.6
0.7
0.7
0.5
0.7
1.1
0.7
0.9
0.9
1.4
1.1
1.0
0.4
1.3
1.5
1.7
1.7
1.2
1.2

3.3
4.1
4.0
5.8
5.1
3.6
3.3
3.8
2.4
1.7
1.9
2.0
4.3
1.4
1.1
0.9
1.6
2.2
2.7

8.3
17.1
13.4
18.2
20.0
12.0
15.4
13.7
10.9
4.8
4.5
5.0
13.0
3.3
4.0
3.4
4.0
6.1
7.3

Measurement temperature 293 K (20 C).

GC studies indicated that all non-biodegraded oils
contain n-alkanes, mainly in the C13±C32 range, with
dominant C17,C19 members. Pr/Ph ratios for these oils
are in the 1.89±3.84 range, ratios of Pr/nC17 and Ph/
nC18 are 0.71±4.67 and 0.26±1.51, respectively (Table 2).
Pr/Ph ratios usually are dependent upon the source of
organic matter and diagenetic transformations,
although as ten Haven (1988) noted, the relationship
between speci®c depositional environments and Pr/Ph
ratio is not fully understood. In general, high Pr/Ph
ratio are associated with oxidising depositional environments or contribution of signi®cant proportions of
terrestrially derived organic matter to the sedimentary
environment. However, it is also suggested that pristane/
phytane ratios increases with increasing migration-fractionation (Curiale, 1996).
In the present study, the whole oil GC analyses
clearly showed that a number of the oils from the eastern
part of the Carpathians Overthrust had undergone one
or more episodes of biodegradation (Fig. 4a and b). A
moderate extent of the biodegradation is documented
based on absence of the C15+-n-alkanes from these oils
and by the presence of pristane and phytane (Fig. 5).
Since the light ends fractions of a crude oil is very sensitive
to factors inducing heterogeneities (source rocks maturity,
pressure and temperature regimes, biodegradation and
water washing) there is growing interest for the detection of compositional variability within this fraction
among di€erent oils. Selected light hydrocarbons para-

meters for the oils from the Potok Fold are reported in
Table 3. The oils have heptane values (H) ranging from
9.93 to 26.14 and isoheptane values (I) less then 1.7.
Normal oils possess heptane values between 18 and 22,
generally associated with values of F between 0.5 and
0.8, representing equivalent vitrinite re¯ectance levels of
approximately 0.86±1.05% (Thompson, 1987). All of
oils discussed in this study have F ratios less then 0.59
(Figs. 6 and 7).
However, the more intriguing aspect of these analyses
was the fact that many of these biodegraded oils also
contained a relatively high concentration of lower
molecular weight hydrocarbons in the range of C4±C11
giving these oils the appearance of having a condensate
entering the reservoir after the initial oil had been biodegraded. It is proposed that in this particular region
the major mechanism responsible for this is migrationfractionation which was initially described by Thompson (1988). He suggested that oil is frequently partially
vaporised in the reservoir and secondly that gas bearing
substantial portions of the oil in solution can be conducted along faults to form independent gas condensate
accumulations. Residual oils formed in this fashion will
show signs of internal fractionation. These are manifested in the conspicuous loss of light ends along with an
increase in the content of light aromatic and naphtenic
hydrocarbons relative to the parans in the residual oil
(indices A and B in Table 3). The process of evaporative
fractionation involves the intersection of an active fault

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I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523

Fig. 3. HC/NSO and Sat/Aro ratios as function of reservoir depth for oils from Potok Fold.

with an accumulation of gas saturated oil. It was postulated that only the saturated vapour migrates along
the fault and this will change the bulk properties of the
oil as well as certain important ratios in the light ends
themselves; particularly enhancing the aromaticity and
naphtenic nature of the light ends of the oil. As an aid to
recognising this e€ect of evaporative fractionation,
Thompson (1988) proposed the use of a number of

ratios based on low molecular weight hydrocarbons.
For example, the residual oils are typically enriched in
aromatics such as benzene and toluene.
The chromatogram of the typical non-front-end loaded oil from Moderowka-6 well (residual oil) is shown
in Fig. 8.
Curiale (1996) suggested that migration-fractionation
leads to changes in parameters traditionally considered

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I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523
Table 2
Geochemical ratios for oil samples based on gas chromatographic analysis
Code

Well

CPITotal

CPI17ÿ23

CPI25ÿ31

nCmax

Pr/Ph

Pr/nC17

Ph/nC18

P-7
S-27A
S-29
P-9
R-37
Mo-6
G-11
M-2
M-3
W-1
W-3
W-6
P-19
E-7
E-13
Po-11
MA-3
K-41
T-10

Polmin-7
SobnioÂw-27A
SobnioÂw-29
Polmin-9
Roztoki-37
ModeroÂwka-6
Gaz-11
Maksymilian-3
Maksymilian-2
Witold-1a
Witold-3a
Witold-6a
Potok-19
Ewa-7a
Ewa-13a
PoznanÂ-11a
Mac Allan-3a
Kronen-41a
Trzes nioÂw-10

1.04
1.03
1.13
1.14
1.08
1.06
1.04
1.05
1.04

1.05
1.05
1.15
1.22
1.11
1.12
1.00
1.12
1.04

1.01
1.00
1.25
0.76
0.76
1.01
1.05
1.05
1.03

17
16
17
16
17
16
19
19
17

1.00
0.96
0.74
1.85
0.85
1.42
1.15
4.67
0.71

0.43
0.51
0.26
1.28
0.54
0.76
0.54
1.51
0.40

1.04

0.99

0.76

16

2.83
2.13
3.84
1.92
2.08
1.93
1.79
2.01
2.23
2.12
2.72
2.59
2.53
1.93
2.19

1.00

0.39

1.89

1.20

0.57

a

27

1.07

1.05

0.76

17
19

Biodegraded oils.

to be predominantly source-in¯uenced (e.g. Pr/Ph, sulphur/nitrogen, d13C di€erences greater than 1.0%) and
maturity-in¯uenced (the ratio of short-chain to long
chain triaromatic steroid and the ratio of the C23-tricyclic terpane to hopane).
In this study, the characterisation of the oils by GC±
MS has shown that the biomarker ®ngerprints are
almost identical for all of the oils examined, regardless
of their degree of biodegradation or condensate content,
suggesting that in all probability these oils were all
derived from the same source (Fig. 9). The m/z 191
chromatograms are generally similar, 17a21b(H)hopanes are dominated by C30 hopane. A decreasing
intensity from C31 to C35 17a21b(H) 22S and 22R
homohopanes is observed indicating the prevailing suboxic depositional environment. The m/z 217 chromatograms demonstrate very similar distribution of regular
steranes. The dominance of hopanes over steranes in
examined oils, excluding Trzesniow oil, (hop/ster ratio
>2.3) suggests that prokaryotic organism were important in the source for these oils. The presence of higher
plant biomarker, e.g. oleanane, indicates that the source
rocks of these oils are Upper Cretaceous to Tertiary in
age. Biomarker maturity parameters indicate that the
oils of the Upper Cretaceous reservoirs in Roztoki,
Sobniow, Polmin and Potok ®elds are the most mature
oils. Relative to other oils, mass fragmentograms m/z
191 and m/z 217 for these oils from west part of the

Potok Fold indicate they have low amount of hopanes
and steranes (Table 4). The low amounts of polycyclic
alkanes in these oils is probably a function of high
thermal maturity. Trzesniow oil, reservoired in the Oligocene Menilite sandstone, appears to be normal
maturity oil based on its whole oil parameters. Its low
maturity sterane patterns (not presented in this paper)
may be due to ''contamination'' from low maturity
Menilite Shales.
With this in mind, and the fact the region is heavily
faulted with reservoirs occurring at many depths as a
consequence of a major tectonic activity in the region
leads to the proposal that migration fractionation is
probably an active mechanism in the region. Over-pressuring of the deeper reservoirs can lead to fracturing of
the cap rocks and escape of the lighter components from
the reservoirs and subsequent release of the pressure. The
lighter components subsequently migrate in to the shallower reservoirs. Variations in the cyclohexane and toluene ratios following the same trends initially proposed by
Thompson (1988) support this hypothesis (Table 3).
In addition to these observations, characterisations of
oils from west to east in the region shows that the
sequence starts from Roztoki-Sobniow and Jaszczew
®elds with nondegraded oils located in deeper part of
the producing trend. The second block in the sequence,
Potok-Turaszowka has lost some n-parans, but
retained most of C18±C20 isoalkanes. Furthermore these

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I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523

Fig. 4. (a) Capillary gas chromatogram (whole-oil analysis) of crude oil from Ewa-7 well; (b) capillary gas chromatogram (whole-oil
analysis) of crude oil from Witold-6 well (continued on next page).

I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523

Fig. 4. (continued)

1517

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I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523

Fig. 5. Total ion chromatograms of C15+ saturated fractions of biodegraded oils from Potok-Turaszowka ®eld (Witold-6, Ewa-7).

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I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523
Table 3
Geochemical ratios calculated from whole oil chromatogramsa
Code

Well

A

B

X

C

I

F

H

P-7
S-27A
A-29
P-9
R-37
Mo-6
G-11
M-2
M-3
W-1
W-3
W-6
P-19
E-7
E-13
Po-11
K-41
T-10

Polmin-7
SobnioÂw-27A
SobnioÂw-29
Polmin-9
Roztoki-37
ModeroÂwka-6
Gaz-11
Maksymilian-2
Maksymilian-3
Witold-1
Witold-3
Witold-6
Potok-19
Ewa-7
Ewa-13
PoznanÂ-11
Kronen-41
Trzes nioÂw-10

1.51
3.42
2.17
3.08
0.70
3.91
1.27
1.88
1.00
1.12
0.91
0.98
1.60
0.24
0.17
1.43
2.97
1.06

1.15
1.16
1.26
1.30
0.95
2.54
1.03
1.13
0.98
0.96
0.91
0.91
0.81
0.90
0.90
0.16
4.16
0.65

1.00
1.15
0.59
1.00
0.49
2.09
0.00
0.58
0.52
0.48
0.48
0.47
0.39
0.56
0.54
0.89
1.72
0.40

0.59
1.38
0.46
1.15
0.52
2.21
0.49
0.46
0.50
0.52
0.56
0.53
0.54
0.75
0.78
0.30
0.42
0.69

0.99
1.65
1.22
0.89
1.66
±
1.45
1.37
1.42
1.38
1.31
1.35
1.26
0.66
0.67
0.51
0.88
1.11

0.45
0.41
0.38
0.45
0.50
0.46
0.45
0.44
0.45
0.49
0.49
0.49
0.46
0.58
0.58
0.26
0.34
0.59

17.63
17.36
17.20
17.50
20.64
21.95
19.09
19.35
19.03
19.70
18.75
19.63
18.61
18.50
18.52
9.93
15.25
26.14

a
De®nitions of compositional ratios: A, benzene/n-hexane; B, toulene/n-heptane; X, xylene (m- and p-)/n-octane; C, (n-hexane+nheptane)/cyclohexane+methylcyclohexane); I, [methylhexanes (2-+3-)]/[dimethylcyclopentanes (1c3-, 1t3-+1t2-)]; F, n-heptane/
methylcyclohexane; H, 100n-heptane/( cyclohexane through methylcyclohexane excluding 1c2-dimethylcyclopentane).

Table 4
Source and maturity related biomarker ratios of oil samples from the Potok Fold
Code

Well

Sterane (%)
C27

P-7
S-27A
S-29
P-9
R-37
Mo-6
G-11
M-2
M-3
W-1
W-3
W-6
P-19
E-7
E-13
Po-11
MA-3
K-41
T-10

Polmin-7
SobnioÂw-27A
SobnioÂw-29
Polmin-9
Roztoki-37
ModeroÂwka-6
Gaz-11
Maksymilian-2
Maksymilian-3
Witold-1
Witold-3
Witold-6
Potok-19
Ewa-7
Ewa-13
PoznanÂ-11
Mac Allan-3
Kronen-41
Trzes nioÂw-10

C28

C29

S/(S+R)

bb/(aa+bb) S/(S+R) Ts/Tm M/C30hop O/C30hop hop/stera

C29aaa

C29ster

ster

33
34
0.33
0.39
Concentration below measurement limit
Concentration below measurement limit
Concentration below measurement limit
Concentration below measurement limit
Concentration below measurement limit
Concentration below measurement limit
Concentration below measurement limit
Concentration below measurement limit
32
34
34
0.42
31
34
34
0.38
33
31
36
0.39
Concentration below measurement limit
30
33
37
0.35
34
34
32
0.37
35
33
32
0.38
32
32
36
0.37
32
29
39
0.46
29
37
34
0.21

C32hop
Low amounts of hopanes

0.42
0.40
0.40

0.57
0.56
0.57

0.82
0.87
0.83

0.15
0.15
0.16

0.17
0.20
0.16

2.26
2.54
2.38

0.36
0.46
0.37
0.42
0.46
0.27

0.56
0.56
0.59
0.56
0.52
0.47

0.77
0.82
1.14
1.11
1.38
0.83

0.16
0.15
0.13
0.12
0.14
0.29

0.13
0.13
0.10
0.18
0.22
0.11

2.82
2.52
3.05
2.70
2.25
1.00

a
hop/ster=17a(H)21b(H)C30 hopane (m/z 191)/ 5a(H)14a(H)17a(H) (20R+20S)C29 and 5a(H)14b(H)17b(H) (20R+20S)C29
steranes (m/z 217).

1520

I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523

Fig. 6. Plot of aromaticity (B=toluene/nC7) vs. paranicity (F=nC7/methylcyclohexane) for Potok Fold oils (after Thompson, 1987;
Holba et al., 1996). Zones: 1, petroleum as generated; 2, higher maturity or source e€ect; 3, early phase fractionation and possible
biodegradation; 4, heavy phase fractionation residual oil; 5, biodegradation.

Fig. 7. Plot of isoheptane value (I) vs. heptane value for Potok Fold oils (after Thompson, 1987; Holba et al., 1996).

I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523

Fig. 8. Capillary gas chromatogram (whole-oil analysis) of residual crude oil from Moderowka-6 well.

1521

1522
I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523
Fig. 9. Mass fragmentograms (m/z 191, m/z 217) showing hopane and sterane distributions in two oils (saturated fractions GC±MS analysis) from Potok-Turaszowka and Jaszczew
®elds.

I. Matyasik et al. / Organic Geochemistry 31 (2000) 1509±1523

degraded oils have an enhanced concentration of the
light hydrocarbons in the condensate range. The third
block in the sequence contains mainly degraded oils
from Kroscienko ®eld, accumulated in the Ciezkowice
Sandstones. The oil from the most eastern part, Trzesniow, appears to be relatively immature. The suspected
``contamination'' of the oil Menilite biomarkers makes
its assignment to any oil family dicult. Additionally,
mixing of oils derived from shales with oils derived from
other source-rocks might be possible, but this requires
further work to be veri®ed.

5. Conclusions
Nineteen oil samples from Potok fold were analysed
to identify oil families and to correlate oils from one
tectonic unit but from separate tectonic blocks.
According to the applied biomarker parameters, all oils
seem to have originated from similar source.
The presence of higher plant biomarker, e.g. oleanane, indicates that the source rocks of these oils are
most likely the Lower Istebna beds.
The most mature from other oils are located in the
west of the Potok fold and are buried at greatest depth.
The Trzesniow oil reservoired in Oligocene Menilite
sands indicates lower maturity. The biomarker traces
suggest that this oil is contaminated with immature
biomarkers from the Menilite Shale.
Biodegraded oils are located in the eastern part of the
Potok fold (Potok-Turaszowka ®eld) and the intensity
of biodegradation is almost constant in the oil ®eld.
Some oils appear to have been biodegraded and then a
second input of light oil has migrated into the reservoirs
diluting the biodegraded oils.
The most probable explanation is migrational fractionation of light oils escaping from deeper over-pressured reservoirs.
The results presented in this paper, may be useful in
clarifying probable mechanisms for oil mixing in this
region, especially mixing of oils derived from Menilite
shales with oils derived from other source-rocks.

Acknowledgements
We are indebted to Dr. M. Chiaramonte, Dr. Sedat Inan
and an anonymous reviewer for constructive criticisms and
suggestions that greatly improved the manuscript.

1523

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