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The 1 st International Applied Geological Congress, Department
of Geology, Islamic Azad University - Mashad Branch, Iran, 26-28
April 2010
Organic Petrography, Geochemical Behavior, and Paleo
Depositional Environment of Binak Oilfield, SW Iran
Fouladvand, Razieh and Alizadeh, Bahram
Department of Geology, Faculty of Earth Sciences, S. Chamran
University of Ahvaz, Iran. Corresponding Author:
[email protected]
Abstract In this study hydrocarbon generation potential and
depositional environment of Pabdeh, Gurpi, Lafan and Kazhdumi
Formatins is investigated using Rock Eval 6 pyrolysis and organic
petrography. Based on Rock-Eval 6 results, organic matter in
Pabdeh, Gurpi and Lafan Formations are mixed Kerogen Types II and
III. Organic matter of Kazhdumi Formation demonstrates prominent
Kerogen Type III. Liptinites, Vitrinites and Inertinites occurrence
altogether, reveal kerogen mixture of Type II and III in Gurpi
Formation. However, abundance of Vitrinite and Inertinit macerlas
in Lafan Formation indicate that Kerogen Type III is prominent. HI
vs OI diagram, demonstrates Pabdeh, Gurpi and Lafan Formations
being deposited in three different facies (B, BC and C). This
reveals that there are terrestrial as well as marine organic
matters in the said formations. Kazhdumi Formation has CD facies
representing an oxidant depositional condition being dominant.
Genetic hydrocarbon potential of Pabdeh, Gurpi, Lafan and Kazhdumi
Formations decreases in the central part of the oilfield due to
activity of Kharg-Mish fault. On the other hand the studied source
rocks towards eastern and western (moving away from its center)
sides of Binak oilfield have a better genetic potential for
hydrocarbon generation. Keywords: Organic petrography and
geochemistry, Depositional Environment, Rock-Eval6.
1. Introduction During the last three decades the Rock-Eval
pyrolysis has been routinely used in organic geochemistry for
examining the oil and gas potential and maturity of different rock
samples (Chang Ryu, 2008). In Iran also few researchers used this
instrument, such as Alizadeh and Moradi in 2007 to geochemically
evaluate Pabdeh Formation in Giant Oilfield of Ahwaz as well as
Zeloi. Optical methods are also used for source rock
characterization but are comparatively require more sample
preparation time (Akinlua et al., 2005). 2. Geological Setting The
study area located at in the vicinity of Persian Gulf at 22 km
northwest of Genaveh port and south of Bibi hakimeh, Rag-e-Safied
and Kilur Karim oilfields (Fig. 1A). In total, 18 wells were
drilled along the axial line of this anticline (Fig. 1B). The
source rocks of this oilfield are Kazhdumi, Lafan, Gurpi and Pabdeh
Formations. During the Albian, Kazhdumi disconformably overlaid
Dariyan Formation. This formation consists of dark and bituminous
limestone interbeded with dark argillaceous limestone and
calcareous shale. In this oilfield, late Certaceous began with
deposition of Coniacian Laffan Shale and completed with deposition
of the Gurpi marls of Campanian to Maastrichtian. Following the
Late Certaceous tectonic activities, the Paleocene-Eocene
transgression resulted in deposition of marls and argillaceous
limestones of the Pabdeh Formation (Motiei, 2007).
mailto:[email protected]
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The 1 st International Applied Geological Congress, Department
of Geology, Islamic Azad University - Mashad Branch, Iran, 26-28
April 2010
3. Methodology and work plan The 43 drill cuttings obtained from
source rocks of wells numbers 2, 4, 6 and 18 were prepared for Rock
Eval analysis by crushing, pulverizing and homogenizing. Then, 50
to 70 mg of sample was loaded in a crucible to perform pyrolysis
with Rock-Eval 6 (Table 1). Later, 21 out of 43 samples were
prepared for incident light microscopy by hand-picking and then
placing cutting particles into a 2.5 cm diameter mold (3 cm deep)
and impregnating with epoxy. After hardening, the sample was ground
using carborundum grits, and finally polished using slurries of
alumina and isopropyl alcohol. Maceral compositions were determined
on polished pellets using a Zeiss Axioplan2 microscope with a 100
oil immersion objective under normal white light. 4. Discussion
This study attempted to understand hydrocarbon potential and paleo
depositional environment of source rocks of Binak oilfield. To
determine the relative ability of source rocks, quantity, quality
and maturation of organic matter was evaluated. 4-1. Quantity of
Organic Matter The TOC content of the studied samples, are
determined to be poor to very good according to Peters, 1986,
classification. The results reveal that TOC of source rocks
decrease toward the center of this oilfield due to the activity of
Kharg-Mish fault (Fig. 2). 4-2. Quality evaluation of organic
Matter by Rock Eval pyrolysis and organic petrography Rock-Eval
pyrolysis data were plotted on a modified Van Krevelen diagram to
evaluate kerogen type. The results indicate that kerogen of the
source rocks in Binak oilfield range from type II to type III (Fig.
3). However, Organic matter of Kazhdumi Formation is dominated by
Type III. Oxidant environments convert hydrogen-rich organic matter
into organic matter with lower H/C (Jones, 1987). The low HI and
TOC values and the high OI value in Kazhdumi Formation from well
number 4 indicate that organic matter composition in this formation
is not dependant only to the original input material, but also to
the availability of oxygen during and after deposition. The abrupt
decrease of HI values in Kazhdumi Formation is probable due to the
remarkable activity of Kharg-Mish Fault during Albian. The Gurpi
and Lafan Formations are distinguished suitable for organic
petrography because of their abundant maceral content. Petrological
observations show that kerogen macerals in Gurpi Formation are
dominated by Type II and III. Organic matter of this formation is
composed of Liptinite (Sporinite), Vitrinite and Inertinte
(Fusinite, Semifusinite and Micrinite)(Fig. 4). The common macerals
of Lafan Formation are Vitrinite and Inertinite (Fusinite and
Semifusinite)(Fig. 4). Similarly, low amount of Hydrogen Index
parameter (249-298 mg HC/g TOC) for this formation reveals that
kerogen Type III is prominent. 4-3. Maturity of Organic Matter
Rock-Eval Tmax values for total samples lies within the oil window
(430 °C - 470 °C) with the exception of Kazhdumi Formation samples
in well number 4. In this formation strong decomposition of organic
material caused anomalies.
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The 1 st International Applied Geological Congress, Department
of Geology, Islamic Azad University - Mashad Branch, Iran, 26-28
April 2010
4-4. Paleo Depositional Environment Jones (1987) defined seven
types of organic facies (A, AB, B through D). The Pabdeh, Gurpi and
Lafan Formations are composed of mixture of organic facies B, BC
and C (Fig. 5). This reveals that there are terrestrial as well as
marine organic matters in the said formations. The Kazhdumi
Formation has organic facies CD representing an oxidant
depositional condition being dominant (Fig. 5). 5. Conclusions The
organic matter of Pabdeh and Gurpi Formations include kerogen type
II/III in this oilfield. Integration of geochemical and
petrographic analysis indicates that the common constituents of
Lafan Formation are kerogen Type III. Diagram of HI vs. OI
demonstrates that the Kazhdumi Formation has deposited in more
oxidant depositional condition in compare with Pabdeh, Gurpi and
Lafan Formations. The low HI and TOC values and the high OI value
in Kazhdumi Formation from well number 4 indicate that organic
matter compositions are not only dependant on the original input
material, but also on the availability of oxygen during and after
deposition. The drastic change in the geochemical data of Kazhdumi
Formation can be due to remarkable increase of the activity of
Kharg-Mish Fault and the flexure forming in basin during the
Albian. It appears that the major factor in variations of genetic
potential of source rocks is activity of Kharg-Mish Fault in this
oilfield. The genetic potential for all source rocks decreases
toward the Kharg-Mish Fault and center of the oilfield. Finally,
this study indicates that the Pabdeh and Gurpi Formations have
capability to generate oil and gas and the Lafan Formation has
potential to generate gas and minor oil. References
[1] Akinlua, A., Ajayi, T. R., Jarvie, D. M. and Adeleke, B. B.,
2005, A Re-appraisal of the application of Rock-Eval pyrolysis to
source rock studies in the Niger delta, Journal of Petroleum
Geology, v. 28, p.39-48.
[2] Alizadeh, B. and Moradi, M., 2007, Geochemical evaluation of
Pabdeh Formation in oilfields of Zeloi and Ahwaz, Shahid Chamran
University Journal of Science, No. 17, p.33-45.
[3] Chang Ryu, I., 2008, Source rock characterization and
petroleum systems of Eocene Tyee basin, southern Oregon Coast
Range, USA, Organic Geochemistry, v. 39, p.7590.
[4] Jones, R.W., 1987, Organic Facies. In: Brooks, J., Welte, D.
(Eds.), Advances in Petroleum Geochemistry, Academic Press, New
York, 1-90.
[5] Motiei, H., 2007, Petroleum Geology of the Persian Gulf,
Tehran University and National Iranian Oil Company, 707p.
[6] Peters, K.E., 1986, Guidelines for evaluating petroleum
source rock using programmed pyrolysis: AAPG Bulletin, v.70, pp.
318-329.
[7] Sherkati, S.H. and Letouzey, J., 2004, Variation of
structural style and basin
evolution in the central Zagros (Izeh zone and Dezful
Embayment), Iran, Marine and Petroleum Geology, v. 21,
p.535554.
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The 1 st International Applied Geological Congress, Department
of Geology, Islamic Azad University - Mashad Branch, Iran, 26-28
April 2010
Table 1. Rock-Eval data from Pabdeh (Pb), Gurpi (Gu), Lafan (La)
and Kazhdumi (Kz) Formations
Pb 2657 672 540 0.12 435 Pb
2520 513 83 1.21 439 Gu 3007 372 272 0.4 434 2560 430 70 1.05
444
La 3211 287 67 2.94 439 2656 314 116 0.51 438 3241 200 93 0.43
435
Gu
2722 220 120 0.8 444 3251 250 92 0.38 438 2760 330 190 0.3
442
Kz
3930 136 252 0.58 422 2818 350 150 3.5 456 3980 64 318 0.44 411
2870 300 180 2.2 457 4005 84 334 0.5 416 2930 209 200 1.9 456 4025
100 586 0.42 421 2972 395 93 0.4 436 4045 110 540 0.3 417 3030 250
160 4.4 456 4060 148 490 0.21 305
La 3208 220 26 4 441
4185 88 676 0.33 411 3224 200 16 16 431 4205 141 539 0.41 426
3260 250 25 4 444
Pb 2621 222 550 0.18 433 Pb 3000 404 164 0.99 439 Gu 2717 289
236 0.53 436 3102 232 296 0.47 436
Table 1. Continued
Gu
2763 312 298 0.41 435
Gu
3402 408 265 0.65 435 2817 271 368 0.38 436 3456 424 209 0.75
434 2865 365 295 0.43 435 3504 412 382 0.4 436 2916 442 280 0.55
436 3562 344 312 0.34 436 2956 279 259 0.29 432 3604 577 131 0.91
438
La 3157 116 242 0.31 332 La
3840 185 107 0.64 447
3878 217 19 11.9 435
Figure 1. Location map of the Zagros oil fields (modified after
Sherkati and Letouzey, 2004) (A) and Well locations on Binak
underground contour map on top of Sarvak Formation (B).
B)(
(A)
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The 1 st International Applied Geological Congress, Department
of Geology, Islamic Azad University - Mashad Branch, Iran, 26-28
April 2010
Figure 2. Column charts frequency (%) versus TOC (wt %) in Binak
oilfield: Pabdeh Formation (A), Gurpi Formation (B), Lafan
Formation (C) and Kazhdumi Formation (D).
Figure 3. Modified Van Krevelen diagram (HI vs. OI).
Figure 4. Digital images of maceral components in Gurpi and
Lafan Formations using a 100 oil immersion objective and under
normal white incident light. Gurpi Formation: Sporinite (A),
Fusinite and Semifusinite (B) and Sporinite, Micrinite and
Vitrinite (C). Lafan Formation: Vitrinite (D) and Fusinite (E) and
(F).
10
(B
Semifusinit10µm
(A Sporinit
Vitrinite10 µm
(C)
(E)
10
1010
(D)
10 µm
10
(F)
(C)
(D
(B)
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The 1 st International Applied Geological Congress, Department
of Geology, Islamic Azad University - Mashad Branch, Iran, 26-28
April 2010
Figure 5. plot of HI versus OI for determination of organic
facie (modified after Jones, 1987). A: Strongly reducing lacustrine
environment, AB: Reducing transgressive marine environment, B:
relatively reducing lacustrine or marine environment, BC: The
environments that consist of terrestrial and marine organic matters
together and have a high sedimentation rate in suboxic environment,
C: Environments with intermediate sedimentation rate in reducing
conditions, CD: Deep environments adjacent to orogeny areas, D:
Strongly oxidant continental environments.