ORGANIC GEOCHEMICAL CHARACTERISTICS OF IRNAK ASPHALTITES ... · Organic Geochemical Characteristics of irnak Asphaltites in Southeast Anatolia, Turkey 59 22S/22S+22R and the values

Oil Shale, 2010, Vol. 27, No. 1, pp. 58–83 ISSN 0208-189X doi: 10.3176/oil.2010.1.07 © 2010 Estonian Academy Publishers

ORGANIC GEOCHEMICAL CHARACTERISTICS OF ŞIRNAK ASPHALTITES IN SOUTHEAST ANATOLIA, TURKEY

O. KAVAK (a)∗ , J. CONNAN (b), N. Y. ERIK (c), M. N. YALÇIN(d)

(a)

Dicle University, Faculty of Engineering and Architecture, Department of Mining Engineering, 21280-Diyarbakır, Türkiye

(b) Laboratoire de Biogéochimie Moléculaire, UMR 7177, Université de Strasbourg, 25 rue Becquerel, 67087-Strasbourg Cedex 02, France

(c) Cumhuriyet University, Faculty of Engineering Department of Geological Engineering 58140, Sivas, Türkiye

(d) İstanbul University, Faculty of Engineering, Department of Geological Engineering, 34850Avcılar, İstanbul, Türkiye

In this study, the organic geochemical properties of asphaltites in Şırnak region in Southeast Anatolia are given in detail. Total organic carbon, Rock-Eval pyrolysis, gas chromatography of saturated fractions, gas chromato-graphy-mass spectrometry and stable carbon isotope (δ13C in ‰/PDB) analysis were conducted on the Şırnak region asphaltite seams. Some of these analyses were performed for the host rocks as well. It is suggested that a live oil seep occurs within asphaltites, which themselves may be formed in a multiple phase system. The amount of total organic matter in asphaltites is high as would be expected, ranging from 12 to 73%. In contrast, this amount is low in the host rocks (0.6–6.3%). The Tmax values are generally between 428 °C and 451 °C. The hydrogen index (HI) values vary between 270 and 541 mg HC/g TOC. The hydrogen index values and Tmax values of the host rocks are significantly lower. The GC analyses have shown that the saturated fractions of all asphaltite samples were not biodegraded. Consequently, organic geo-chemical parameters such as Hopane/Hopane+Moretane, Ts /Tm,

∗ Corresponding author: e-mail [email protected], [email protected]

Organic Geochemical Characteristics of Şirnak Asphaltites in Southeast Anatolia, Turkey

59

22S/22S+22R and the values of %C27, %C28, %C29 steranes obtained as a result of GC-MS analysis were used for maturity assessments. Although the organic geochemical parameters provided some data for the origin and placing mechanism, it is concluded that they are not sufficient for an overall conclusion, especially concerning placing mechanism. Therefore, new studies particularly on local and regional geological aspects need to be undertaken.

Introduction

Asphaltite is a solid petroleum fuel with a high softening point. It contains high amounts of sulfur and volatile substances. Its melting point is approximately 200–315 °C. The raw material is also defined as dark-colored solid petroleum, formed through metamorphosis and principally composed of hydrocarbons containing very little or no oxygenated compounds and crystallizable paraffins [1]. Generally, asphaltic materials are considered to be formed by migration of petroleum and solidification in cracks during tectonic movements [2, 3].

Asphaltite is composed of hydrocarbons and polar compounds, associated with trace metals such as molybdenum, vanadium, nickel and uranium [4]. Asphaltic veins or asphaltites contain large quantities of authigenic minerals similar to those which precipitate within black shales, including clay minerals, quartz, albite, orthoclase and framboidal pyrite [5]. They are known to have high ash levels and to be rich in metals including Mo, Ni and Ti [6]. Turkish asphaltite, which contains high amounts of petroleum, can be used as solid fuel after the petroleum has been extracted. Within this scope, the possibilities for the use of asphaltites in thermal power plants as solid fuel have also been explored [5].

The total reserve of asphaltites in Turkey is 81,940,000 tons, and 45,473,000 tons of this total amount is visible reserve [7, 8] (Table 1). Şırnak asphaltites contain high amounts of ash and sulfur and their calorific

Table 1. Reserve characteristics of asphaltic veins

Reserve (1000 tons) Location name Measured Indicated Inferred Total Grand total Mineable

Harbul-Silopi 17 914 7 851 – 25 765 25 765 7 000 Silip-Silopi 3 071 1 335 – 4 406 4 406 – Üçkardesler-Silopi 9 472 10 881 – 20 352 20 352 – Avgamasya 7 481 673 – 8 154 8 154 7 000 Milli 2 000 2 900 1 600 6 500 6 500 – Karatepe 500 2 000 2 500 5 000 5 000 – Seridahli 3 534 1 254 1 279 6 067 6 067 – Nivekara 300 1 000 700 2 000 2 000 – Ispindoruk 100 500 500 1 100 1 100 –

O. Kavak et al.

60

value is high. Average values for the asphaltites are reported to be as follows (wt.%): total moisture 1–5.3, ash 33–45, sulfur 4.1–6.4, volatile matter 24–40, fixed carbon 47–59, hydrogen 3.2–5.6, and solubility in CS2 4.9–30 [9–10]. Due to combustible sulfur content it is assumed that asphaltites will create important environmental pollution problems if burned without any physical cleaning procedures. The asphaltites, containing dominant carbonate minerals (calcite and dolomite), will produce CO2 from the breakdown of carbonate minerals, when burned.

Asphaltite occurrences in the Şırnak and Silopi regions in Southeastern Anatolia are found as fault and crack fills in NE-SW and NW-SE trending veins and fractures which were formed by N-S directional forces. The veins are observed in the Cudi Group (Triassic-Jurassic), Germav Formation (Upper Cretaceous-Paleocene), Gerçüş Formation (Eocene) and Midyat Group [11] (Figures 1, 2).

At first glance the easily accessible asphaltites or more likely the oil seeps associated with the asphaltites may have been mined in antiquity to be used as bitumen. Bitumen is present on potsherds in some antique sites, e.g. Kütnüs Höyük, Nervan Höyük and Takyan Höyük, south of the asphaltite vein district [12, 13]. The run-of-mine asphaltite from mainly open-pit mines is directly consumed for domestic heating without any physical cleaning. The quality of these asphaltite reserves is poor in terms of their ash and sulfur contents. Nevertheless, asphaltite is utilized not only as a fuel alternative to coal, but also as a source of trace metals and for the production of ammonia. Asphaltite can be converted into a variety of secondary products such as light hydrocarbon gases and tar by pyrolysis [14].

Various studies have been conducted on the asphaltic components placed in the fractures in different formations in the South East Anatolian region

Fig. 1. Location map of the investigated asphaltites.


61

Fig. 2. Geological map of investigated area.

and on their origin and placement mechanisms. Some studies were done in order to define and classify these occurrences. They were defined as carbon-rich hydrocarbons [15], as a substance between asphaltite and asphaltic pyro-bitumen [4] or as an asphaltic substance [11]. In these studies it was stated that they have an asphalt origin, which arose from a bituminous level deeper or which migrated through fractures upwards from a petroleum-bearing zone [1, 11]. They were formed as a result of the alteration of aromatic-inter-mediate petroleum during migration [3]. The petroleum was emplaced in fractures during a multi-phase migration and was subjected to biodegrada-tion [16]. The asphaltite from veins shows similarities with Raman-Dinçer petroleum in terms of chemical composition, and therefore both are probably originated from the same source [17]. In the studies conducted by Turkish Petroleum Corporation (TPAO) it was stated that Triassic-Jurassic Cudi Group might be the source of the asphaltite [16]. However, according to other studies, in which the potential of the Cudi Group was evaluated, source rock potential of this unit is low [18]. Other studies on the geological and geochemical characterization of the asphaltites of the region were conducted by Ekinci et al. [15, 17], and Khalimov et al. [19]. These authors proposed various interpretations of the origin and classification of the asphaltites [12, 18–20]. Review of the pertinent literature reveals that the definition, origin, and formation of the asphaltite seams remain inconclusive.

O. Kavak et al.

62

The objective of this study is to present a detailed information on the organic geochemical and organic petrographic characteristics of the asphaltite veins in SE Turkey which have to be considered as an additional energy resource in Turkey (Figures 2, 3).

Fig. 3. View of outcrops of Avgamasya and Harbul asphaltite veins.


63

Regional geology

The main oil-producing region of Turkey is Southeast Anatolia. The area is located at the northern margin of the Arabian plate. This plate, as well as its northern extension, was part of the Gondwana continent in the southern hemi-sphere during Palaeozoic time. During Palaeozoic, SE Turkey was affected by epirogenic movements as part of the Arabian Plate. These movements were most probably created by the Caledonian and Hercynian orogenies which caused major structural deformation during the Palaeozoic in SE Turkey and the Arabian Plate [20, 21]. During Mesozoic time, a substantial carbonate platform was developed along the southern margin of the Neotethys Sea in a passive continental margin setting [22]. Beneath are Palaeozoic shelf-type successions inferred to have accumulated along the northern margin of Gondwana [23]. The initial stages of southward obduction of ophiolites resulted in subsidence of the Arabian Platform and deposition of Campanian-Maastrichtian terrigenous sediments [23, 24]. The intervening southerly Neotethys basin remained partly open in the Early Tertiary, and it was finally closed by diachronous collision in Eocene-Miocene time, followed by further convergence and overthrusting during late Miocene. After the onset of westward “tectonic escape” of the Turkish Plate in the Early Pliocene, south-eastern Turkey was transected by the East Anatolian Transform Fault. Today, southern Turkey records a post-collision setting [22, 25].

South of Şırnak where the asphaltite veins are observed, the oldest outcropping unit is Permian limestones of the Tanin Group. Triassic Goyan group overlies this unit which is generally composed of limestone and dolomites. On the upper part, there are Jurassic-Cretaceous Cudi group units represented by limestone and dolomites. The unit, in which asphaltite veins are found in the south of Şırnak, is the Upper Cretaceous-Palaeocene Germav formation, which is composed of marl, argillaceous limestone and sandstone levels (Fig. 4). The Upper Palaeocene Gerçüş formation, in which Harbul, Üçkardeşler and Silip veins are found, has the characteristics of a continental facies. This formation, located south of the E-W striking over-thrust line around Harbul-Silip in the south, is concordant over the Germav formation. Eastward a lateral transition with Becirman limestone is observed. The Gercüş formation is overlain by Mid-Eocene aged Midyat limestones. To the south, Miocene aged Şelmo formation is at surface.

Southeastern Anatolia gained its present day structural configuration by the collision of the Anatolian and Arabian plates in Mid-Miocene along the Bitlis suture zone [20]. The asphaltite veins were formed as a result of the N-S directional compression tectonics and fractures developed longitudinally (in Silopi region) and were filled with liquid/semi solid asphaltic matter to or towards the surface.

Twelve asphaltite occurrences within and around the Şırnak region namely Avgamasya, Milli, Anılmış-Karatepe, Seridahli, Nivekara, İspindoruk, Segürük, Harbul (Aksu), Silip, Üçkardeşler, Rutkekurat and Uludere Ortabağ-Ortasu

O. Kavak et al.

64

Fig. 4. Stratigraphic column of the investigated area.

were evaluated in this study (Fig. 1). Apart from these twelve occurrences, there are also the Şırnak-Hebiş, Dergül, Ceffane, Gündükiremo, Besiri, Batman-Gerçüş and Şikeftikon occurrences which are not very significant.

Most of the asphaltite veins in the Şırnak region (Avgamasya, Milli, Seridahli, Nivekara, Karatepe, İspindoruk, Seğürük) are in form of NE-SW directional fracture fillings in the Germav formation. The vein of Avgamasya is up to 15–100 m wide and 3500 m long. The Segürük vein is smaller with about 5–10 m wide and 140 m long. However, the İspidoruk and Rutkekurat veins are within the Cudi Group carbonates. The Üçkardeşler, Harbul and Silip veins, located in the Silopi region, were developed parallel to bedding in the Gerçüş formation. The Harbul and Üçkardeşler veins are also parallel to


65

the overthrust plane. These veins were formed as a result of the filling of the fractures, which were developed in front of the overthrust zone, by asphaltic bituminous mixtures. The Silip vein is a lenticular occurrence formed parallel to an anticlinal fold.

According to Khalimov et al. [26], natural bitumens can be divided into three main groups layered, vein and contact bitumens, according to their geological locations and formation mechanisms. Layered bitumens are generally formed as a result of the contact of reservoir rocks with oxygen. Vein bitumens are generally composed of petroleum migrating into fracture systems through “phase migration”. Harbul natural bitumens around Şırnak were classified as bitumens formed as veins. It was also stated by Khalimov et al. [26] that such bitumens are common in the Taurus-Zagros zone.

Methods

The locations of the veins from the study area were determined through field work and descriptions of the veins were made. Organic geochemical evalua-tion of 61 asphaltite samples, collected from the veins, was performed. Based on data obtained from these analyses, extraction, liquid column chromatography, GC, GC-MS and isotope analyses were performed on seven samples.

Investigated asphaltite samples were prepared for petrographic analysis using standard procedures [27]. The maceral and mineral composition of the samples were studied using reflected and transmitted normal and fluore-scence microscopy. Petrographic studies of asphaltites and hostrocks included quantitative analyses of maceral groups, as well as minerals by use of an Axioplan microscope. For this investigation, the samples were crushed to a maximum size of 1 mm and embedded in epoxy. Sample preparation and reflectance determinations were performed at MTA MAT Laboratory (Ankara, Turkey). Eleven samples were prepared for maceral analysis and analyzed petrographically [4]. Measurements were performed by using a Leitz MPV-Geor system under reflected white and fluorescent light. Reflectance values (Ro) were measured at 548 nm using a Leitz Ortholux microscope MPV2, a glass standard Leitz Rair 1.24%; a halogen lamp, an oil-immersion objective 32/0.65 and an EMI 9592 S-11 photomultiplier.

To gain some insight into the organic geochemistry of asphaltite veins, TOC-Rock-Eval pyrolysis was performed on selected samples. Rock-Eval pyrolysis provides information on the amount and type of organic matter and its level of maturation in a sedimentary rock [28]. The samples were pulverized, then pyrolyzed using a TOC-Rock-Eval-II analyzer following techniques outlined by Espitalié et al. [29] and Peters [30]. S1, S2 S3, Tmax, hydrogen index (HI), oxygen index (OI), production index (PI) values were determined. The samples were analyzed in the Research Group Laboratories of the Turkish Petroleum Corporation (TPAO – Turkey).

O. Kavak et al.

66

For biomarker analyses, seven representative samples were extracted for approximately 40 hrs. using dichloromethane (CH2Cl2) in an ASE 300 (Accelerated Solvent Extraction device). After extraction, the extract yields were calculated and the deasphalted extracts were fractionated by liquid column chromatography. The saturate fraction was analyzed by Agilent 6850 GC in TPAO Research Group Center Laboratories according to ASTM D 5307-97 (Ankara, Turkey). Individual compounds were identified by comparison of mass spectra and retention times in the Total Ion Current chromatogram (TIC). Relative concentrations of different compound groups in investigated asphaltites, and saturated hydrocarbon fractions were measured using peak heights from the gas chromatograms. The saturate fractions were also analyzed by selected ions monitoring (m/z 191 and 217), gas chromatography-mass spectrometry (GC-MS) using an Agilent 7890A\5975C GC-MS spectrometer. The aliphatic composition and carbon preference index (CPI) values were calculated from the gas chromatograms.

Minerological components and petrographic determinations

Generally, asphaltite deposits of Mesozoic-Cenozoic age contain high amounts of quartz, pyrite, carbonates and clay minerals [5]. Mineralogical analysis of these investigated asphaltite samples indicate high amounts of carbonate minerals such as calcite, dolomite, ankerite and siderite. In addition, pyrite, mica, sphalerite, quartz, clay and titanium minerals were also determined.

The mineral matter of the asphaltites, determined from XRD analyses, is mainly composed of calcite, dolomite, pyrite, quartz, illite and subordinate quantities of feldspar and gypsum. Karayiğit et al. [9, 10], found the asphaltites, analyzed by ICP-AES and ICP-MS, to be enriched in Cd, Cr, Cu, Mo, Ni, Sb, Se, Tl, U, V and Zn. Concentrations of Bi, Dy, Er, and Gd in some samples exceed the currently available ranges for these elements in most world coals. Cd was detected in sphalerite and Cd-Zn-sulfide, Ni in pentlandite, and traces of Ni, Cu, Zn, V, and Cr in pyrites [9, 10].

Samples of eleven asphaltites were mounted in polished blocks for reflectance measurements of bituminite. The average reflectance of natural asphaltites is: Rmax: 0.26% (stdev: 0.02%), and for the hostrock, Rmax: 0.48% (stdev: 0.03%). Some petrographic characteristics of the veins are given below:

Milli vein; asphaltite with large pores and a pyrite content of 4% which is low when compared to other asphaltites. Because its Rmax value is 0.38%, its volatile matter is assumed to be high. Clay and similar inorganic matter content reaches 13%.

Harbul vein; asphaltite of a very dark color. The Rmax value is very low and the amounts of pyrite (10%) and inorganic matter (20%) are high.

Seridahli vein; metamorphosed asphaltite with an increased value of Rmax (1.42%). The pyrite content is 5%, clay and other inorganic matter – 17%.


67

Segürük vein; The asphaltite has large pores and it is light grey. The Rmax value is 0.66%. Pyrite with amounts to 14% is mostly filling voids. Clay and other inorganic matter comprise 6%.

Avgamasya vein; The asphaltite has a fine aspect and contains 15-micron pores on average. Pyrite with amounts up to 12% is mostly filling voids. Rmax value is 0.54%. Clay and other inorganic matter comprise 20%.

Organic geochemistry

The geochemical analysis was conducted by following the analytical flowchart applied to study petroleum and source rocks. Results of TOC analysis and Rock-Eval pyrolysis, made on 61 samples, are reported in Table 2. Extraction and Iotrascan analysis were limited to nine samples, and gas chromatography, gas chromatography-mass spectrometric spectra of saturated fractions were acquired on seven samples only. TOC analyses

The amount of TOC is high as one would expect for asphaltites varying between 12 and 73% (Table 2). Although the host rock values are lower (0.6-6.3%), they still remain as fair source rocks. The TOC value in the Avgamasya vein averages 42.2%. Significant differences in TOC between host rocks and asphaltites indicate that host rocks were not extensively invaded with bitumen during the filling of the vein. Natural asphalt did not penetrate into the host rock due to its low porosity. Rock-Eval pyrolysis

Interpretation of Rock-Eval data (Table 2) was based on parameters and experimental limits documented by Espitalié et al. [29] and Peters [30]. For the samples studied, HI values are quite high, averaging 309 mg HC/gTOC, whereas Oxygen Index values are very low, contrary to expectations deduced from the published papers (4 mg HC/g TOC on average).

Tmax values range between 440 and 479 °C (446.2 °C on average). A value of 609 °C recorded in a sample taken from the Segürük vein belongs to a single sample that underwent high temperatures by burning naturally. Therefore this value is not representative of the asphaltite of this seam. The pyrolysis data of host rocks are quite low when compared to the asphaltites.

In the Tmax-HI diagram, the asphaltites are classified as Type-II kerogen, whereas the organic matter in the host rocks corresponds to Type-II-Type-III kerogen (Fig. 5). The asphaltites were determined as mature to post mature according to the Tmax values. [31-33].

O. K

avak

et a

l. 68

Tab

le 2

. TO

C a

nd R

ock-

Eva

l pyr

olys

is d

ata

of t

he in

vest

igat

ed a

spha

ltit

e sa

mpl

es

Asp

hal

tite

Loca

tion

S

amp

le

Nu

mb

er

TO

C,

%

S1

, m

g H

C/g

TO

C S

2,

mg

HC

/g T

OC

S3

, m

g C

O 2/g

TO

C P

I,

mg

HC

/g T

OC

) H

I,

mg

HC

/g T

OC

O

I,

mg

CO 2

/g T

OC

Tm

ax,

°C

Avg

amas

ya

21

1

2.1

–4

9.5

1

0.1

8–

22

.4

9

9.7

1–

16

5.3

0

.2–

3.0

9

0.0

6–

0.1

6

25

1–

11

02

0

–8

4

40

–4

51

S

egü

rük

10

3

7.8

–4

3.6

1

.15

–2

4.7

1

.47

–2

26

.41

0.2

6–

2.8

0

.05

–0

.44

4–

50

7

1

–1

3

43

7–

60

9

Har

bu

l 1

1

46

.9–

65

.1

0–

32

.7

0.0

1–

28

3.4

0

.07

–1

.9

0.0

6–

0.1

1

0

–5

69

0

–3

4

28

–4

79

K

arta

l 3

4

4.6

–4

9.4

1

0.1

7–

13

.53

2

34

.7–

25

8.4

0.2

3–

0.8

4

0.0

4–

0.0

5

52

2–

52

7

0–

2

43

3–

43

7

Çift

çile

r 3

2

9.7

–4

4.9

1

2.9

–2

2.5

15

8–

23

2.6

4

2.2

1

0.0

6–

0.0

9

49

9–

53

1

1–

4

43

5–

44

0

Ku

mça

tı

2

3

9–

41

.9

6

–6

.6

14

4.3

–1

55

.4

1.3

–1

.7

0.0

4

37

0–

37

1

3–

4

44

6–

44

8

Ser

idah

li 1

3

1–

73

7

.48

4

0.2

3

0.6

1

0.1

6

12

6

1

46

5

Kar

atep

e 1

4

9.4

1

7.5

2

60

.04

0

.61

0

.23

1

21

1

4

65

N

ivek

ara

1

53

.1

10

.09

7

5.4

9

0.4

9

0.1

2

14

2

0

46

4

Mill

i 1

4

5

10

.91

8

9.9

5

0.7

3

0.1

1

19

9

1

45

6

Ho

st R

ock

s 7

0

.7–

6.3

0

.13

–0

.61

0

.65

–4

.3

0.3

1–

0.4

8

0.0

9–

0.2

1

17

–2

76

8

–5

2

42

7–

44

2

68 O. Kavak et al.


69

Fig. 5. HI-Tmax diagram of the investigated asphaltites and hostrock samples.

Extraction and biomarker analyses

In addition to Rock-Eval pyrolysis, precipitation of asphaltenes and liquid column chromatography analysis of desasphalted extract were carried out on 9 samples in order to determine percentages of saturated and aromatic hydrocarbon, resins and asphaltenes (Table 3).

Saturated and aromatic hydrocarbons were examined by gas chromato-graphy followed by computerized GC-MS. No obvious evidence of bio-degradation has been recorded in the saturated (Fig. 6) and aromatic (Fig. 7) hydrocarbons of asphaltites. n-Alkanes are present in all samples, and their low amounts in some asphaltites (Fig. 6) seem more likely related to low to moderate maturities than to biodegradation. This assumption agrees with OI values of asphaltites which are extremely low and therefore consistent with a lack of biodegradation and oxidation in these samples. Biodegradation has been observed in host rock samples which are acting as petroleum reservoirs and may have allowed bacteria to consume hydrocarbons.

O. K

avak

et a

l. 70

Tab

le 3

. Qua

ntit

y, y

ield

and

gro

ss c

ompo

siti

on o

f C

H2C

l 2 e

xtra

ct f

rom

asp

halt

ites

, δ13

C o

f as

phal

tene

s an

d bi

omar

ker

rati

os

Sam

ple

n

um

ber

(d

ata

ban

k)

Loca

tion

%

EO

, w

eigh

t %

Le

co T

OC

, %

/sam

ple

%

EO

/TO

C E

xtra

ct,

pp

m

Sat

ura

tes,

%

A

rom

atic

s,%

R

esin

s,

%

Asp

hal

ten

es,

%

δ13C

as

ph

alte

nes

, ‰

PD

B

Ts/

Tm

G

A /

C

30α

βH

22

65

1

-Seg

uru

k 5

.29

4

0.7

1

3.0

5

3

5.8

2

3.1

3

4.3

3

6.8

–

26

.8

0.0

4

0.0

07

2

26

6

2-S

erid

ahli

2.0

8

38

.7

5.4

2

07

76

3

0.6

4

6.3

1

8.4

4

.7

–

–

–

22

67

3

-Avg

amas

ya 7

.52

4

4.2

1

7.0

7

5

8.3

4

1.7

3

5.8

1

4.2

–

26

.8

0.0

5

0.0

07

22

68

4

-Kar

talte

pe

11

.39

4

7.5

2

4.0

1

14

3

.3

27

.4

31

.8

37

.5

–2

6.8

0

.05

0

.00

7

22

69

5

-Ku

mca

ti 2

.41

3

9.5

6

.1

24

08

6

6.9

3

2.4

2

6.5

3

4.2

–

26

.8

0.1

7

0.0

14

22

70

6

-Mili

3

.40

3

4.1

1

0.0

3

4

8.

3

38

3

3.9

1

9.8

–

26

.6

0.4

9

0.0

2

22

71

7

-Kar

atep

e 2

.05

3

9.7

5

.2

20

53

5

41

.1

38

.7

18

.1

2.1

–

–

–

22

72

8

-Har

bu

l 2

1.6

7

49

.6

43

.6

21

7

4.1

2

7.2

3

6.2

3

2.5

–

26

.9

0.0

15

0

.00

5

22

73

9

-Niv

ekar

a 1

.93

4

3.9

4

.4

1

93

48

2

6.3

4

9.2

2

1.1

3

.4

–

–

–

–

no

t d

eter

min

ed

70 O. Kavak et al.


71

Fig. 6. Continues.

Abundance

Abundance

Abundance

O. Kavak et al.

72

Fig. 6. Continues.

Abundance

Abundance

Abundance


73

Fig. 6. GC-MS analysis of C15+ saturates: TIC from nine asphaltite veins.

Abundance

Abundance

Abundance

O. Kavak et al.

74

Fig. 7. Continues.

Abundance

Abundance

Abundance


75

Fig. 7. Continues.

Abundance

Abundance

Abundance

O. Kavak et al.

76

Fig. 7. GC-MS analysis of C15+ aromatics: TIC from nine asphaltite veins.

Abundance

Abundance

Abundance


77

GC-MS analysis revealed distributions of terpanes (m/z 191) and steranes (m/z 217) as shown by a sample taken from the Segürük vein (Fig. 8). Identification of key molecules is presented and diagnostic biomarker ratios were calculated when possible (Tables 3 and 4). In fact high maturities, expected on the basis of Rmax, HI and gross composition of extracts for Seridahli, Karatepe and Nivekara, are confirmed by steranes and terpanes. These biomakers are indeed almost absent in these samples and no ratios could be calculated (Table 3). Harbul appeared again as the less mature sample with a Ts/Tm ratio of 0.015. The rates of sterane isomerization (20S/20S+20R) and bishomohopane isomerization (22S/22S+22R) indicate that isomerization is not fully completed, and therefore maturity of the samples is less than 0.8–0.9% Ro. Maturities in asphaltites cover a wide range from samples as Harbul at the top of the liquid oil window to samples in which steranes and terpanes have completely disappeared.

Carbon isotopic values (δ13C in ‰/PDB) on whole samples (Table 4) provide information which is not representative of the organic matter present in the raw asphaltite material for these values are obviously influenced by carbonates, present in the mixture. δ13C is shifted from 2-4 δ13C as shown when comparing bulk values to data on asphaltenes (Table 3) which are all around -27 ‰/PDB. Isotopic values on asphaltenes combined with some molecular ratios (Fig. 9) such as Ts/Tm and Gammacerane/C31αβHopane (GA/C31αβH) show that asphaltites are clustering in the same area and are likely belonging to the same genetic family. In addition asphaltites are well differentiated from other famous oil shows analysed in southeast Turkey namely Eruh, Şelmo, Boğazköy and Yeşilli. As a consequence, bitumen coatings of some potsherds at Nervan, Kütnüs, south of the Şırnak district, do not seem to have originated from oil seeps associated with asphaltite veins (Fig. 9).

Table 4. Biomarker ratios and isotope values of asphaltites

Vei

n lo

catio

n

Sam

ple

ref

eren

ce

Typ

e o

f sa

mp

le

δ13C

wh

ole

as

ph

altit

e,

‰ /

PD

B T

s/T

m

(su

rfac

e ar

ea)

Ts/

Tm

(p

eak

hei

gh

t)

Ho

pan

e /

Ho

pan

e +

C3

0M

ore

tan

e (s

urf

ace

area

)

Ho

pan

e /

Ho

pan

e +

C3

0M

ore

tan

e (p

eak

hei

gh

t)

22

S /

22

S +

22

R

(C3

1αβH

op

ane)

su

rfac

e ar

ea 2

2S

/ 2

2S

+ 2

2R

(C

31α

βHo

pan

e)

pea

k h

eig

ht

Avgamasya JK46 host rock – 0.35 0.31 0.84 0.89 0.52 0.54

Seguruk JK47 host rock – 0.2 0.13 0.87 0.88 0.56 0.57

Avgamasya JK51 host rock –23.6 0.21 0.18 0.84 0.92 0.52 0.55

Seguruk JK48 vein –25.7 0.07 0.04 0.88 0.91 0.5 0.54

Seguruk JK50 vein –23.6 0.47 0.3 0.89 0.94 0.6 0.6

Ciftciler JK49 vein –23.3 – 0.06 0.87 0.9 0.54 0.55

Avgamasya JK52 vein –24.8 0.15 0.14 0.72 0.88 0.55 0.57

– not determined

O. Kavak et al.

78

Fig. 8. GC-MS analysis of C15+ saturates: TIC, terpane (m/z 191) and sterane (m/z 217) mass fragmentograms of an asphaltite (Segürük, n 2265).

Org

anic

Geo

chem

ical

Cha

ract

eris

tics

of Ş

irnak

Asp

halti

tes

in S

outh

east

Ana

tolia

, Tur

key

79

0

0.51

1.52

2.5

-30

-29.5

-29

-28.5

-28

-27.5

-27

-26.5

-26

Hos

t roc

ks

Asp

ha

ltite

vei

ns

Eru

h

Hak

emiU

se +

Kav

usa

nHak

em

iUse

Ner

van

Sel

mo

Sel

mo

Haz

ro

Haz

ro

Haz

ro

Ts

/ Tm

δ13 C

asp

(in

‰/

PD

B)

0

0.2

0.4

0.6

0.81

1.2

00.5

11.5

2

Ts

/ Tm

GA

/ C

31αβ

H

Ne

rva

n

Ye ş

illi

Kü

tnüs Eru

hH

ake

miU

se +

Ka

vusa

n

Boğa

zkö

yD

emir

köy

Hö

yük

Se

lmo

Ha

zro

Asp

hal

tite

s

Fig

. 9.

Mo

lecu

lar

ratio

s (G

A/C

31αβ

H,

Ts/

Tm

) an

d δ13

C o

f as

pha

ltene

s: c

om

par

iso

n o

f as

pha

ltite

s w

ith o

il se

eps

(Eru

h, Y

eşi

lli,

Şel

mo

, B

oğa

zkö

y) a

nd a

rcha

eo

logi

cal b

itum

ens

(Ha

kem

i Use

, K

avu

şan,

Ne

rva

n, K

ütnü

s, D

em

irkö

y).

Organic Geochemical Characteristics of Ş irnak Asphaltites in Southeast Anatolia, Turkey 79

O. Kavak et al.

80

Discussion and conclusions

The veins were placed in fractures at high angles to the bedding of the Campanian-Maestrichtian Germav Formation and Jurassic-Triassic Cudi group units. But the asphaltite occurrences in the Palaeocene-Lower Eocene Gercüş formation are mainly parallel to bedding

The organic matter present in the asphaltite material has reached various degrees of maturities which were initially seen by the Rock-Eval characteristics (HI vs. Tmax) and confirmed by GC-MS properties of C15+ alkanes and C15+ aromatics and as well as by some Ro values obtained by petrographic analysis of the organic matter. This evaluation of the states of maturation, using present-day techniques, confirmed the pioneering study of Orhun [4] who concluded that varied degrees of geothermal alteration of the asphaltites occurred among the veins. In this respect, the asphaltites of Seridahli, Karatepe and Nivekara are the most mature whereas asphaltites of Harbul and Kartaltepe are the least mature.

The high Tmax values and reflectance data indicate that bitumens were injected in place under temperatures reached within the oil and gas condensate windows. Asphaltites, rich in total organic matter, contain organic material with a Type-II kerogen aspect and are of mid to high maturities.

The high values of the hydrogen index (HI), coupled with low oxygen index (OI), indicate a rather high hydrocarbon potential and a very low level of oxidation. The high production index (PI) means that there are significant amounts of liquid hydrocarbons as well. No significant biodegradation was recorded in both the C15+ saturated and the C15+ aromatic hydrocarbons

The existence of bitumen with different chemical and physical charac-teristics indicates that asphaltites were formed at different stages of the thermal degradation of their related source rock. The source of asphaltites around Şırnak was discussed by several authors. Bartle et al. [3] stated that the Avgamasya asphaltite was derived from some high-sulfur, aromatic-inter-mediate petroleum. Ekinci et al. [18] pointed out that Harbul asphaltite derived from marine organic matter deposited under anoxic conditions. In agreement with these characteristics, Cretaceous carbonate units are found in south-eastern Anatolia Region [34]. Nevertheless, the source rock evaluation performed in particular on the Cudi group strata reveals that the asphalt from asphaltite did not originate from the Cudi group carbonates and evaporites.

In regions where tectonic movements are intense, the development of new fractures or fault lines may open new ways of migration from reservoirs to surface, and brings the underlying petroleum closer to the surface at different times. For this reason, hydrocarbons have the characteristic of live petroleum under the solid bitumens located at the surface in the field of study and may be considered as indicative of potential petroleum reserves in the depths.


81

Acknowledgements

This study was performed with support from Dicle University Research Fund Project No. DÜAP–2000-MF–403 and DÜAPK–03-MF–85. Within this scope, we would like to thank Dr Selami Toprak (MTA) and Assoc. Prof. Dr. Sedat İnan (TÜBİTAK-MAM) for their special concern and support. The entire staff of TKİ Şırnak, especially Adil Tunç, Meki Aydın and all colleagues who have contributed, are kindly acknowledged. REFERENCES

1. Lebküchner, R. F. Occurrences of the asphaltic substances in Southeastern Turkey and their genesis // Bulletin of the Mineral Research and Exploration Institute of Turkey. 1969. Vol. 72., P. 72–74.

2. Kural, O. Coal: Resources, Properties, Utilization, Pollution. – Istanbul: Kurtis Press, 1994 [in Turkish].

3. Ekinci, E., Bartle, K. D., Frere, B., Mulligan, M., Saraç, S. The nature and origin of harbulite and related asphaltite from southeastern Turkey // Chem. Geol. 1981. Vol. 34, No. 1–2. P. 151–164.

4. Orhun, F. Characteristic properties of the asphaltic substances in Southeastern Turkey, their degrees of metamorphosis and their classification problems // Bulletin of the Mineral Research and Exploration Institute of Turkey. 1969. Vol. 72. P. 97–109.

5. Parnell, J. Timing of hydrocarbon-metal interactions during basin evolution, Source, transport and deposition of metals // Proceedings of the 25 years SGA Anniversary Meeting, Nancy, 1991. Vol. 25. P. 573–576.

6. Saltoglu, T., Akyuz, T., Alparslan, E. Quantitative determination of molybdenum, nickel, vanadium and titanium in the asphaltites and asphaltite ashes by XRF-spectroscopy // Bulletin of the Mineral Research and Exploration Institute of Turkey. 1978. Vol. 91. P. 89–93.

7. Gönenç, O. Asphaltites and Asphaltite Deposits of Turkey. – A report of MTA, 1990 [in Turkish].

8. Şengüler, İ. Energy valve and potential of asphaltite and bituminous shale in Turkey. – Turkey 6th Energy Congress, 2007. P. 186–195 [in Turkish].

9. Karayigit, A. İ., Querol, X. Mineralogy and elemental contents of the Şırnak asphaltite, Southeast Turkey // Energ. Source. 2002. Vol. 24. P. 703–713.

10. Karayigit, A. I., Gayer, R. A., Querol, X., Onacak, T. Contents of major and trace elements in feed coals from Turkish coal-fired power plants // Int. J. Coal Geol. 2000. Vol. 44, No. 2. P. 169–184.

11. Erdem-Şenatalar, A., Ekinci, E., Keith, D., Bartle, K. D., Frere, B. Hydrocarbon minerals from South-Eastern Turkey – A comparison of the chemical natures of the neighbouring Raman-Dincer crude oil and Avgamasya Asphaltite // Erdöl & Kohle, Erdgas Petrochemie. Bd. 44, Hft. 7/8, 1991. P. 298–300.

12. Kavak, O., Yalçın, M. N. Organic geochemical properties of Şırnak asphaltites. – 14th International Petroleum and Natural Gas Congress and Exhibition of Turkey. 2003, 12–14 May, Ankara, Turkey. International Proceedings. 2003. P. 185–187 [in Turkish].

O. Kavak et al.

82

13. Kavak, O., Connan, J., Yalçın, M. N., Jarvie, B., Jarvie, D. Geochemical characterization of the asphaltite veins from the Şırnak area, southeastern Turkey: their use as archaeological material. – IMOG 2007, Torquay, UK.

14. Harput, B., Harput, A. Geochemical evalvation of Seridahli (Şırnak) asphaltites of South-east Anatolia. – Turkey Petroleum Congress, 16–20 April 1990. P. 92–106 [in Turkish].

15. Ekinci, E., Pakdel, H., Jones, D. W., Bartle, K. D., Olcay, A., Özel, F. The organic geochemistry of Harbul and Avgamasya asphaltites // Chim. Acta Turc. 1981. Vol. 9. P. 465–473.

16. Taşman, C. E. Harbolite, a carbonecaous hydrocarbon // Am. Assoc. Petr. Geol. Bull. 1946. Vol. 30. P. 1051.

17. Ekinci, E., Saraç, S., Bartle, K. D. Characterization of pyrolysis products of harbolite and Avgamasya asphaltites: Comparison with solvent extracts // Fuel. 1982. Vol. 61, No. 4. P. 346–350.

18. Yalçın Erik, N., Özçelik, O. Organic facies variation from well data on the Cudi Group, the Eastern part of SE Turkey // Geochem. Int. 2007. Vol. 11. P. 1245–1255.

19. Khalimov, E., M., Klimushin, I. M., Ferdman, L. I., Goldberg, I. S. Geological problems of natural bitumens. – 11th World Petrol. Congr., Bristol, UK. PD1 (5). 1983. P. 1–14.

20. Hiçyılmaz, C., Altun, N. E. Improvements on combustion properties of asphaltite and correlation of activation energies with combustion results // Fuel Process. Technol. 2006. Vol. 87, No. 6. P. 563–570.

21. Dewey, J. F., Pitman, W. C., Ryan, W. B. F., Bonnia, J. Plate tectonics and the evolution of the Alpine system // Geol. Soc. Am. Bull. 1973. Vol. 84, No. 10. P. 3137–3180.

22. Bambach, R. K., Scotese, C. R., Ziegler, A. M. Before Pangea: the geographies of the Palaeozoic world // Am. Sci. 1980. Vol. 68. P. 26–38.

23. Şengör, A. M. C., Yılmaz, Y., Sungurlu, O. Tectonics of the Mediterranean Cimmerides: nature and evolution of the western termination of the Paleo-Tethys // Geological Society, London, Special Publications. 1984. Vol. 17, No. 1. P. 77–112.

24. Al-Laboun, A. A. Stratigraphy and hydrocarbon potential of Palaeozoic succession in both Tabuk and Widyan Basins, Arabia // Future Petroleum Provinces of the World. AAPG Memoir / M. T. Halbouty (ed.). 1986. Vol. 40. P. 373–397.

25. Bozdoğan, N., Erten, T. Age and effects of Mardin uplift South-East Anatolia. – Turkey 8th Petroleum Congress, 1990. P. 207–227 [in Turkish].

26. Khalimov, E. M., Klimushin, I. M., Ferdman, L. I., Goldberg, I. S. Geological factors in the formation of deposits of natural bitumens // Int. Geol. Rev. 1985. Vol. 27, No. 2. P. 187–193.

27. Bustin, R. M., Cameron, A. R., Grieve, D. A., Kalkreuth, W. D. Coal Petrology: Its Principles, Methods and Aapplications (Short Course Notes). Vol. 3, 3rd ed. – Geological Association of Canada, 1989. 278 p.

28. Espitalié, J., Madec, M., Tissot, B., Menning, J. J., Leplat, P. Source rock characterization method for petroleum exploration. – Proc. Ninth. Annual Offshore Technology Conf. 1977. Vol. 3. P. 439–448.

29. Espitalié, J., Deroo, G., Marquis, F. Rock-Eval pyrolysis and its applications. Part 2. // Rev. Inst. Fr. Pét. 1985. Vol. 40, No. 6. P. 755–784.


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30. Peters, K. E. Guidelines for evaluating petroleum source rock using pro-grammed pyrolysis // Am. Assoc. Petr. Geol. Bull. 1986. Vol. 70. P. 318–329.

31. Altun, N. E., Hicyılmaz, C., Kok, M. V. Effect of particle size and heating rate on the pyrolysis of Silopi asphaltite // J. Anal. Appl. Pyrol. 2003. Vol. 67, No. 2. P. 369–379.

32. Kok, M. V., Pamir, R. Pyrolysis kinetics of oil shales determined by DSC and TG/DTG // Oil Shale. 2003. Vol. 20, No. 1. P. 57–68.

33. Tonbul, Y., Saydut, A. Thermal behavior and pyrolysis of Avgamasya asphaltite // Oil Shale. 2007. Vol. 24, No. 4. P. 547–560.

34. Yalçın Erik, N., Özçelik, O., Altunsoy, M., İlleez, H. İ. Source-rock hydrocarbon potential of the Middle Triassic-Lower Jurassic Cudi Group units, Eastern Southeast Turkey // Int. Geol. Rev. 2005. Vol. 47, No. 4. P. 398–419.

Presented by A. Siirde Received September 28, 2009

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ORGANIC GEOCHEMICAL CHARACTERISTICS OF IRNAK ASPHALTITES ... · Organic Geochemical Characteristics of irnak Asphaltites in Southeast Anatolia, Turkey 59 22S/22S+22R and the values