Journal of Kirkuk University – Scientific Studies , vol.3, No.

2,2008

Geochemical Characterization of the Oil in the Tertiary

Reservoir in Bai-Hassan Oil Field / Northern Iraq

Dler H. Baban
College of Science -University of Sulaimani

Abstract

An oil sample from the Tertiary reservoir in the well BH-22 in Bai –Hassan Oil Field,
Northern Iraq has been analyzed by the means of GC and GC/MS. The identified
biomarkers and the stable carbon isotopes indicated a low salinity marine carbonate
depositional environment for the precursor organic matters of the oil. CPI, 20S/
(20S+20R) C29ST, ββS/ (ββS+ααR) C29ST and other maturity biomarkers showed a
moderately mature oil. Non effect of biodegradation has been found out from the ratios of
P1, P2, and P3 and from the absence of 25-Norhopane biomarker. A Star diagram has
been drawn for the analyzed oil sample as a finger print using C9 – C20 alkanes.

Introduction
The minor giant oil field of Bai-Hassan is locates near Kirkuk in North
Iraq. The field has been discovered in 1953 by the Iraqi Oil Company (IPC)
and having come on production in 1960. The structure of the field is about
40km long and about 3.5 km wide and consists of a longitudinal, sinusoidal,
asymmetrical anticline. The southern limb of the structure is steeper(37°-65°)
than the north eastern limb (22°-35°). The structure of Bai-Hassan consists
of two main domes of Kithka at the southern east and Daoud at the western
north. The two domes are separated by Shahal saddle which its base is about
90m deeper than Daoud dome’s crest. The crest of Kithka Dome is 335m
higher than Daoud dome’s crest.

The studied oil sample and the research methods

The studied oil sample has been taken from the well BH-22 from the
Tertiary Main Limestone reservoir. The well locates at the coordinate 43°
57' 41.8" E and 35° 38’ 25 8" N (fig.1).The whole oil sample analyzed by
GC, while the GC/MS analysis done for the saturate compounds and that in
Baseline Resolution, Inc. (Analytical Laboratories) in Houston, USA. Tens
of peaks have been measured through the two analyses reflecting the
 Journal of Kirkuk University – Scientific Studies , vol.3, No.2,2008

properties of the analyzed oil sample. Saturate and aromatic C¹³ isotopes and
the API for the oil sample also have been measured. A number of
relationships between different peaks have been plotted to obtain
information about the source and depositional environment of the initial
organic matters (precursors), maturity stage, biodegradation effect, in
addition to draw the star diagram finger print for the analyzed oil sample.
Table (1) contains the ratios and values of the majority of the used
biomarkers in this study.

Fig.(1): Location map of the studied BH-22 well.

Table (1): The ratios and values of the majority of the used biomarkers in
this study.

C27Dia/
Dias./Ster. %C27 %C28 %C29
Pr/Ph Pr/(Pr+Ph) Pr/nC17 Ph/nC18 (Dia+Reg.Ster)
(217m/z) (217m/z) (217m/z) (217m/z)
(217m/z)

0.89 0.47 0.26 0.34 0.25 0.23 40.5 23.8 35.7

20S/(20S+
C29H/C30 δ13C C29 ββS / (ββS
C35H/C34H δ13C 20R)
H aromatic + ααR) %P1 %P2 %P3
(191 m/z) saturate C29ST
(191 m/z) (217m/z)
(217m/z)

1.43 1.16 -27.1 -27.1 0.45 0.36 31.89 16.05 4.48

Journal of Kirkuk University – Scientific Studies , vol.3, No.2,2008

Source and paleodepositional environment of the precursor

organic matters
Broocks et al. (1969)in Philp,(2004) noted the presence of the regular
isoprenoids pristane (Pr) and phytane (Ph) in crude oils and coal extracts. This
led Powell and Mickidy,(1973)in Philp,(2004)to propose a mechanism for the
production of relatively high concentrations of pristane in oxic type
environments and high concentration of phytane in reducing type environments.
Thus, the Pr/Ph ratio evolved as an indicator of the oxicity of the initial organic
matter’s depositional environment.The Pr/Ph ratios are very helpful in
determining the paleodepositional environment and source of the precursor
organic matters of the reservoired oils. It is well known that Pr/Ph ratios more
than 3.0 indicates predominantly non marine source from terrestrial organic
matter,(terrigenous plant input) deposited under oxic to suboxic conditions
(Peters et al.,2005).An oil accumulation have Pr/Ph ratio less than 0.8 indicates
saline to hypersaline conditions associated with evaporate and carbonate
deposition, while marine organic matters usually have Pr/Ph less than 1.5 (Peters
et al.,2005).As the Pr/Ph ratio for the analyzed oil sample is 0.89, therefore a
marine influence on the type of the source organic matters can be detected.The
plot of the Pr/nC17 and Ph/nC18 values for the analyzed sample on the cross plot
in the figure-2 indicated a mature marine source of organic matter (mostly type II
kerogen) deposited in a reduced condition with less effect of biodegradation.
10
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er
s K
Ty rre

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re II

gl

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tu /I
Te

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g ine en
ix II

str
cin ar og
m pe

Ox
du m er
Ty

idiz
re al, II K

ing
al pe
Ty

Re
g

2.0 du
cin
g
Pristane / C17

n
io
at

1.0
ad
gr
e
od
Bi

n
io
at

0.5
ur
at
M

0.3

0.2

0.1
0.1 0.2 0.5 1.0 2.0 5.0 10
Phytane/ C18

Fig (2): Pristane/C17 versus Phytane/C18 cross plot for the studied
oil sample.
Journal of Kirkuk University – Scientific Studies , vol.3, No.2,2008

Hypersaline lakes and ponds often develop anoxic conditions if saline

deep water is covered with water of lower density. Sedimentary rocks that
were deposited under these conditions often contain high relative
concentrations of gammacerane, which is a biomarker generally associated
with water column stratification (Sinninghe Damste et al., 1995 in Brooks
and Summons,2004). The measured gammacerane Index (gammacerane/
hopane)(191m/z) for the analyzed oil sample was so little(0.13) indicating
deposition in a low salinity marine environment. Because some biomarkers
pointed to specific taxa, they can also act as indicators of specific habitats.
Fresh water environments are often indicated by the presence of biomarkers
of typical fresh water organisms such as Botryococus braunii. Lacustrine
conditions are often indicated by the predominance of algal steroids (Chen
and Summons,2002 in Brocks &`Summons,2004). Rearranged steranes
(diasteranes) are relatively more abundant in clastic sediments than in
carbonates (van Kaam-Peters et al.,1998 in Brooks &Summons,2004).
However increase in thermal maturity is also a key factor in the conversion
of biomarkers to their rearranged forms. The cross plot of Pr/Pr+Ph and C27
/(C27Dias.+Reg.Ster.)(fig.3) indicates mostly anoxic carbonate environment
of deposition. The relative abundance of C27,C28, and C29 also supported
the marine carbonate environment of deposition for the precursor organic
matters of Bai-Hassan oil as it appears from the ternary of C27,C28,and C29
in the figure (4). 0.8
Anoxic
0.7 Shales
Suboxic
strata
0.6
Pr /(Pr + Ph)

0.5
Anoxic
0.4 Carbonates

0.3

0.2

0.1
0.1 0.2 0.3 0.4 0.5 0.6 0.7
C27 Dia/(Dia+Reg Steranes)

Fig (3): The cross plot of Pr/(Pr+Ph)versus C27 Dia/(Dia+Reg.Sterane),

from which anoxic carbonate source of organic matters is clear for the
analyzed sample
Journal of Kirkuk University – Scientific Studies , vol.3, No.2,2008

C28
100%

10 10
20 20
30 30 Non-marine shale
40 Marine > 350 M.Y.
40
Marine carbonates
50 50 Marine shale

60 60

70 70
80 80

90 90

100 100
90 80 70 60 50 40 30 20 10
C27 C29
Fig (4): Ternary diagram of C27, C28, and C29 Sterane.

Anoxic, carbonate condition of deposition has also detected from the relation
ship between the ratios of Diasterane / Sterane with C29H / C30H (fig.5)
and C29H / C30H with C35H / C34H (fig.6).

Carbonate content
Diasteranes / Steranes

2.0

1.6

1.2

0.8
Shale

0.4

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
C29H / C30H
Fig (5): Diasterane/Sterane versus C29H/C30H cross plot showing the
influence of Carbonate on the sources of the organic matters.
Journal of Kirkuk University – Scientific Studies , vol.3, No.2,2008

Anoxic condition
2.0

1.6
C29H/C30H

1.2

0.8

Carbonate
content
0.4

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

C35H/C34H
Fig (6): The cross plot of C29H / C30H versus C35H / C34H

Stable Carbon Isotope

The stable carbon isotopic composition of organic matter is an important
tool with which to differentiate algal and land plant source materials and
marine from continental depositional environments (Meyers, 2003 in Youns
and Philp 2005).Zein El-Din and Shaltout(1987)in Youns and Philp(2005)
concluded that the stable carbon isotope values of crude oils are dependent
mainly on the depositional environment of the source rock and the degree of
thermal maturity at which the oil was expelled.The carbon isotopic signature
of bitumen is relatively heavy for predominantly higher plant sourced oil
(Killops et al.,1997).From the plot of δ13C saturate versus δ13C aromatic ratio
(fig.7) a marine or slightly mixed origin oils has been detected.
-16
(PDB)

-18
% (PDB)

OILS OF TERRIGENOUS ORIGIN

% (PDB)

-20
LS
OI
-22 IN
IG
OR
Aromatics

-24 ED
Aromatics

IX
M OILS OF MARINE ORIGIN
-26

-28 ine
ar
d¹³ C

g m
sin
δ¹³C

-30
c rea ence
In flu
-32 in
-34 -32 -30 -28 -26 -24 -22 -20 -18
δ¹³CCSaturates
d13 Saturates%%
(PDB)
(PDB)
Fig(7): Cross plot of δ13C saturate versus δ13C aromatic for the analyzed oil sample.
Journal of Kirkuk University – Scientific Studies , vol.3, No.2,2008

Maturation
The gas chromatogram of the saturated hydrocarbon fractions shows a
shift in the normal alkane distribution to lower carbon numbers (fig.8),
reflecting relatively a moderate level of thermal maturity , The analyzed oil
sample is isotopically light sample (saturate fractions is-27.1‰ and aromatic
fractions is also-27.1‰PDB);this can be interpreted according to Cooper et
al.,(1993) in Justwan, et al.,(2005) in terms of increased type II kerogen
contribution. The Carbon Preference Index(CPI) which generally is
presented by the following equation:
1  (C 25  C 27  C 29  C 31  C 33) (C 25  C 27  C 29  C 31  C 33) 
CPI  
2  (C 24  C 26  C 28  C 30  C 32) (C 26  C 28  C 30  C 32  C 34) 
can offer valuable information on the maturation of source rocks and
reservoired oil. High CPI values(above1.5) always refer to relatively
immature samples. Low CPI values, however, do not necessarily mean
higher maturity; they can also mean a lack of higher n- alkanes stemming
from terrestrial input. The measured CPI value for the studied oil sample
was equal to 0.98 which means that it is moderately mature oil. The cross
plot of the two maturity indicator biomarkars20S/(20S+20R) C29ST versus
ββS/(ββS+ααR)C29ST,(fig.9)shows a moderately mature oil.According to
Hunt (1996) the Thermal Equilibrium Value (The end point of the reaction
in the oil generation zone (Brooks et al., 1992 in Othman, 2003) for S/(S+R)
C29ST (ααα) biomarker is 0.5 (approximately comparable to 0.9%Ro), and
for ββS/(ββ+ααR)C29ST biomarker is 0.70 (approximately comparable to
0.9%Ro). Accordingly, the estimated maturities as comparable Vitrinite
Reflectance for the studied oil have been calculated and appeared to be
0.65 %Ro using S/(S+R) C29ST (ααα) biomarker and 0.58 %Ro using
ββS/(ββ+ααR)C29ST biomarker, indicating a moderate stage of maturity.
The measured API gravity for the studied oil sample (23.9°) may support the
moderate maturity of the oil.

Fig.(8): The GC chromatogram for the analyzed oil sample.

Journal of Kirkuk University – Scientific Studies , vol.3, No.2,2008

%C29 20S/(20S+20R) 55

50

40

t u rity
35 Ma

0
0 40 50 60
%C29 ββ / (ββ + ααR)
Fig.(9): 20S/(20S+20R) C29ST versus ββS/(ββS+ααR) C29ST cross plot
shows a moderately mature oil.
Biodegradation
The biodegradation of petroleum and other hydrocarbons in the
environment is a complex process, whose quantitative and qualitative
aspects depend on the type, the nature, and amount of the oil or hydrocarbon
present; in addition to the seasonal environmental conditions (such as
temperature, oxygen, nutrient, water activity, salinity, and acidity (pH)), and
the composition of the allochthonous microbial community (Wang et al.,
2006). In general, the degradation of hydrocarbons is ranked in the following
order of decreasing susceptibility: normal-alkanes more than branched
alkanes more than low molecular weight aromatics more than high
molecular weight aromatics and cyclic alkanes (Garrett et al., 1998 in Wang
et al., 2006). Mango (1994) established a P1, P2, P3 diagram based on C 7
data to show the effect of biodegradation on the oils or extracts. In the
diagram; P1 represents the straight chain C 7 n-alkane; P2 represents mono-
branched C7s while P3 includes the poly-branched C7s, according to Mango;
this plot seems to be very sensitive measure of biodegradation. Using
Mango’s ternary diagram of P1, P2, and P3 for determining the effect of
biodegradation on the studied oil sample (fig10), a non effect of
biodegradation has been noticed. According to Peters et al., (2005),25-
norhopanes occur in oils where the hopanes were preferentially removed, but
are absent where the hopanes show greater bioresistance than the steranes.
Journal of Kirkuk University – Scientific Studies , vol.3, No.2,2008

Many biodegraded oil contain abundant 25-norhopanes, and high

abundance is evidence for severe biodegradation(rank more than or equal to 6)
(Trendel et al., 1990 in Peters et al., 2005). As the analyzed oil sample of
BH-22 contain no 25-norhopanes, therefore no sever biodegradation activity
can be suggested.

P3
100
90 10

70 30

50 Original oil 50

30 B
70
Tr iode
en gr
d ad
at
ion
10 90

100 90 70 50 30 10 100
P1 P2
Fig.(10): P1. P2 and P3 ternary diagram shows a non biodegraded
oil of BH-22.
Star Diagram
Kaufman et al. (1990) developed a sensitive method, called Reservoir Oil
Fingerprinting (ROF), for recognizing differences in the gas chromatograms
of oils. Kaufman et al’s ROF procedure consists of first numbering all small
measurable peaks sequentially through n-C20. Then they visually select
fewer than 25 pairs of peaks (usually 12 or so) and calculate the ratios of
their peak heights or areas. Peaks are mainly selected in the C9 – C20 range
where there is a good distribution of naphthenes and aromatics without too
much overlap. The next step is to construct a star diagram (polygon plot) by
plotting each peak ratio on a different axis of a polar plot. The figure (11)
shows the star diagram or the fingerprint of the analyzed oil sample
depending on it’s containing of C9-C20 normal paraffin (Table 2). This
diagram and the chromatograms of the GC/MS analysis (fig.12) will mark
the oil of the Tertairy reservoir in Bai-Hassan oil field.
Journal of Kirkuk University – Scientific Studies , vol.3, No.2,2008

C15
C14
10. C16
08.0
6.0 C17
C13
4.0
2.0
C12 C18

C19
C11

C10 C20
C9
Figure (11): Star diagram for the analyzed oil sample
using C9 – C20 peak values.
Table (2): The ratios of the nrmal paraffins from C9 to C20 used in drawing the star Diagram for the
analyzed oil sample.
C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20
8.12 8.63 9.03 8.36 8.07 7.34 7.19 6.08 5.44 4.75 4.11 3.79

Conclusions
 The precursor organic matters of the analyzed oil sample of BH-22
well are from a low salinity marine carbonate depositional
environment.
Figure (12): GC / MS chromatograms for the analyzed oil sample from BH-22 well.
 The studied oil sample is isotopically light and appears to be mostly of
type II kerogen origin.
 The oil is moderately mature.
 No biodegradation activities affected the analyzed oil sample.

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‫التمثيل الجيوكيميائي للنفط الموجود في مستودع العصر الثالثي‬
‫في حقل باى حسن النفطي‪ /‬شمال العراق‬

‫دلير حسين بابان‬

‫قسم الجيولوجي‪ /‬جامعة السليمانية‬

‫المستخلص‬
‫أجريت تحاليل كروماتوكراف الغاز (‪ (GC‬و كروماتوكراف الغاز‪/‬طيف الكتلي‬
‫(‪ (GC/MS‬لنموذج من النفط الموجود في مستودع العصر الثالثيي فيي ل يل يان لسين النف يي فيي‬
‫شييماا العييراظه أ قييرا دييي الييتاةا الحياتييير و كسيين كليياقر الكر ييوا المسييت ر ي ا المييواد الع ييوير‬
‫األولير للنموذج النف ي المتروس ديت تربي ت فيي يبير حريير كار وكاتيير دليلير الملوليره أميا اليتاةا‬
‫الحياتير الخاصر تحتيت الن وج الحرارن و المتمثلر عامل التفاضل الكر وكي )‪ (CPI‬و‬
‫‪ 20S/ (20S+20R) C29ST‬و ‪ ββ/ (ββ +αα) C29ST‬ف ت أكتا ا النموذج النف ي المحليل‬
‫هييو كاضييا لراريييا صييور‪ .‬معتتلييره أمييا كسيين ‪ P2 ,P1‬و ‪ P3‬ل ع ييقا ال ي عغ و يييا ‪C25-‬‬
‫‪ Norhopane‬ضمن كتاقا التحليل ف ت دلت على عتم تي ثر الينفط المحليل التكسير الحيياتي أو الن ياط‬
‫ال كتيرنه من كالير أخرى‪ ,‬ف ت ت رب ال كل ألنجمي ك صمر إ قام خاصر نفط العصير الثالثيي فيي‬
‫ل ل ان لسن و ذلك اعتمادا على كسن الكر وكاا من (‪ )C9‬إلى (‪)C20‬ه‬