Comparison of the general chemical nature of various kerogens based on their reactivities towards bromine

Org. Geochem. Vol.6, pp. 383-390,1984 Printedin Great Britain.Allrightsreserved

1)146-6380/84$03.00+00.00 Copyright © 1984PergamonPress Ltd

Comparison of the general chemical nature of various kerogens based on their reactivities towards bromine PETAR A. PFENDT Institute of Chemistry, Faculty of Sciences, University of Belgrade, ll001 Belgrade, P.O. Box 550, Yugoslavia

Abstract--It was found that data obtained by bromination of kerogens, such as the amount of bromine consumed and the amount of hydrogen bromide liberated, in combination with data obtained by ultimate analysis (C, H) provide a basis for a more detailed comparison of the chemical nature of fossil organic materials than the one on the basis of O/C-H/C ratios only. Kerogens of the following shales were investigated: Estonian Kukersite (Middle Ordovician), Australian Torbanite (Permian-Carboniferous), Kimmeridge shale, Dorset, U.K. (Jurassic), Colorado shale (Eocene, Green River Formation) and Aleksinac shale, Yugoslavia (Oligocene-Miocene). The kerogens were compared with each other as well as with their benzene bitumens, and one sample of petroleum asphaltenes. The data obtained by bromination and by elemental analysis were introduced into an atomic C/Br vs H/HBr diagram, divided into nine areas by means of bromination lines H/HBr = a(C/Br), obtained on the basis of theoretical consideration of the behaviour of eight structural models of fossil organic materials towards bromine. Thc order of areas occupied by kerogens in the C/Br vs H/HBr diagram, from left to right, i.e. starting with lower C/Br values towards higher values, strictly followed the arrangement of the kerogens in the Van Krevelen diagram. However, in the C/Br vs H/HBr diagram details were observed which were useful for a closer characterization of the chemical nature of the organic matter. Two principal indicators of the chemical nature of the organic substances were found: (a) the distance of the position of an investigated substance from the beginning of the coordinating system (C/Br vs H/HBr diagram), and (b) the region which an investigated substance occupies between two bromination lines.

Key words: asphaltenes, C/Br vs H/HBr diagram, kerogens (chemical nature, elemental analysis, reactivity towards bromine), Van Krevelen diagram

INTRODUCTION The investigations of the organic substance of old sediments, undertaken during the last 20 years through the use of modern analytical methods, have enabled us to gain considerable knowledge about the composition and structure of this substance. In this way the models for the structure of the organic substance of vitrinite (Given, 1960), the BurlingameH a u g - S c h n o e s - S i m o n e i t model of C o l o r a d o kerogen (Burlingame et al., 1969), the Djuri~idMurphy-Vitorovid-Biemann model of Colorado kerogen (Murphy et al., 1971), the Schmidt-Collerus and Prien model of Colorado kerogen (Yen, 1976), Yen's model of asphaltenes (Vandenbroucke, 1980) and Colorado kerogen (Yen, 1976), and the TissotE s p i t a l i d - D u r a n d - V a n d e n b r o u c k e model of kerogen type II (Oberlin et al., 1980) were designed. Moreover, the kerogens are classified into three basic types according to their position in the H/C vs O/C diagram (Tissot and Welte, 1978). The purpose of this investigation was a more detailed comparison of the general chemical nature of certain types of kerogen with each other as well as with the corresponding benzene soluble bitumens using elemental analysis data and data about the reactivity of these substances towards bromine. The approach follows from the fact that certain structures, depending on their chemical nature, react

with a definite amount of bromine with the formation of a definite amount of hydrogen bromine which is also characteristic for a given type of structure. Bromine and bromine reagents have been applied a number of times in the investigation of the kerogen structure (Pfendt and Vitorovid, 1973; Vitorovid and Pfendt, 1974; Pfendt, 1975; Vitorovid et al., 1977; Costa Neto et al., 1980). By linking data about the reactivity of organic substances from ancient sediments towards bromine with elemental analysis data, which have proved to be of great value for the classification of kerogen, we thought that the comparison of the general chemical nature would be more precise. As a basis for comparison the C/Br and H/HBr ratios were chosen, i.e. the value for the number of carbon atoms in the organic substance for which one bromine atom is consumed and the number of hydrogen atoms for which one molecule of hydrogen bromide is liberated. We have chosen kerogens of different types and age for comparison: the kerogen of the Estonian Kukersite (Middle Ordovician), Australian Torbanite (Permian-Carboniferous), British Kimmeridge shale (Jurassic, Dorset), Colorado shale (Eocene, Green River Formation) and Yugoslav shale from Aleksinac (Oligocene-Miocene). At the same time the corresponding benzene-soluble bitumens were 383

384

PETARA. PFENDT

compared as well as an asphaltene fraction from the Yugoslav "Velebit" oil. EXPERIMENTAL

Preparation of kerogen concentrates The shale samples were ground in a ball mill to a DIN-60 grain size, treated with 2 M HCI on a steam bath for a period of 4 h and then filtered, washed, dried at 80°C and extracted with benzene in a Soxhlet apparatus. The concentrates were classified using standard DIN-sieves. Three samples of each concentrate were investigated: the total unsieved sample and the -0.050 + 0.040 mm and the - 0.040 mm fractions. The kerogen content in the concentrates (Table 1) was determined according to the method described by Jovanovid and Vitorovid (1952), and the values obtained were corrected for the content of silicate crystalline water. These corrections were based on separate elemental analyses of silicates which previously were obtained by wet combustion of organic matter from the kerogen concentrates (Pfendt and Vitorovid, unpublished data).

Preparation of the asphaltene fraction from oil A sample of Yugoslav paraffin-base oil ("Velebit") was refluxed for 1 h with petroleum ether (b.p. 40-70°C) in the amount 30 cm 3 g oil- 1. After standing for a period of 2.5 h, the suspension was filtered through filter paper S+S 5893 and the obtained asphaltene precipitate was extracted in a Soxhlet apparatus with petroleum ether for a period of 25 h. The crude asphaltenes were then dissolved in ben-

zene also by extraction in a Soxhlet apparatus. After removal of benzene on a steam bath, the refined asphaltenes were dried in a drying oven at 60°C. The elemental analysis of the organic substances (Tables 1 and 2) was performed by means of microprocedures and the results were corrected for the content of crystalline water in the silicates of the examined kerogen concentrates (Pfendt and Vitorovid, unpublished data). The determination of bromine consumption and of the amount of liberated hydrogen bromide was performed according to the previously described procedure (Pfendt and Vitorovid, 1973; Vitorovid and Pfendt, 1974; Pfendt, 1975). Briefly, the kerogen concentrates were brominated as a suspension in a solution of bromine in carbon tetrachloride for48 h in the dark at 20°C. The excess of bromine and the amount of hydrogen bromide liberated were determined by titration with a standard solution of sodium thiosulphate. The bitumens were brominated in the form of their benzene solutions (Table 3).

Methodology On the basis of the elementary composition data of the investigated organic substances and the data about their behaviour towards bromine (Table 3), we have calculated the values for the number of carbon atoms for which one bromine atom is consumed (C/Br), and the number of hydrogen atoms for which one molecule of hydrogen bromide is liberated (H/HBr), due to substitution, oxidation and elimination reactions (Table 3). The values so obtained were then entered in a C/Br vs H/HBr diagram which is divided into nine regions by means of the bromina-

Table 1. The content of kerogen in the concentrates, atomic H/C and O/C ratios

No.

Shale

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Kukersite (a)* Kukersite (b) Kukersite (c) Torbanite (a) Torbanite (b) Torbanite (c) Kimmeridge (a) Kimmerdige (b) Kimmeridge (c) Colorado (a) Colorado (b) Colorado (c) Aleksinac (a) Aleksinac (b) Aleksinac (c)

Kerogen content (%)

H/C

O/C

Type

76.89 79.80 76.65 81.73 79.79 77.26 61.69 62.79 52.42 39.114 42.78 34.24 28.61 30.43 29.22

1.522 1.583 1.453 1.548 1.483 1.482 1.289 1.324 1.372 1.460 1.509 1.576 1.379 1.42(I 1.5(12

0.154 0.168 0.162 0.022 0.031 0.017 0.193 0.244 0.199 0.099 (I. 106 0.088 0.166 0.225 0.229

II-I II-I II I I I II II II I I I II II lI

*(a), (b) and (c) refers to the unsieved, the -0.050 + 0.040 and the -0.040 mm samples, respectively.

Nature of kerogens based on their Br activities Table 2. Bitumens, atomic H/C and O/C ratios No.

Shale

H/C

O/C

16 17 18 19 20 21

Kukersite Torbanite Kimmeridge Colorado Aleksinae (Asphaltenes)

1.633 1.429 1.347 1.7(15 1.679 1.077

0.171 0.065 0.088 0.055 0.071 0.018

tion lines H/HBr = a(C/Br). These lines were obtained by theoretical consideration of the behaviour of eight known structural models (Figs 1-5) of organic substances of ancient sediments towards bromine and by calculating their C/Br vs H/HBr values (Table 4). Theoretical bromination lines for the distinct fossil organic substances were found in the following way. Firstly, the maximal n u m b e r of bromine molecules which could be consumed by the certain structural model was calculated on the basis of the known chemical behaviour (Roedig et al., 1960; Patai, 1973) of the distinct structural types (alkanes, alkenes, aromatic hydrocarbons, primary, secondary or tertiary alcohol, etc.). Similarly, the n u m b e r of hydrogen bromide molecules (due to substitution, oxidation

385

and elimination reactions) was calculated. From the values so obtained and the molecular formulas of the structural models, C/Br and H/HBr ratios were calculated and then entered in the C/Br vs H/HBr diagram. Each of these points was connected with the beginning of the coordinating system and straight lines obtained represented theoretical bromination lines. On each line were all substances with the same structural characteristics as the particular structural model observed. The individual investigated organic substances of ancient sediments have various positions in relation to the bromination lines of the structural models. The indicators of the general chemical nature of the investigated substances are: (1) the distance of the position of an investigated substance from the beginning of the coordinating system; (2) the region which the investigated substance occupies between two bromination lines. The distance of an investigated substance's position from the beginning of the coordinating system is inversely proportional to the reactivity of the substance towards bromine. Substances which are found on one particular bromination line but at different distances from the beginning of the coordinating system have the same C/Br vs H/HBr ratios, hence they have a high degree of chemical similarity. The region between two bromination lines of the models of fossil organic substances which the investi-

Table 3. Reactivity data of the kerogens and bitumens towards bromine Bromine consumption (mmol g 1)

HBr liberation (mmol g l)

C/Br

H/HBr

Kerogens 1 Kukersite (a)* 2 Kukersite (b) 3 Kukersite (c) 4 Torbanite (a) 5 Torbanite (b) 6 Torbanite (c) 7 Kimmeridge (a) 8 Kimmeridge (b) 9 Kimmeridge (c) 10 Colorado (a) 1l Colorado (b) 12 Colorado (c) 13 Aleksinac (a) 14 Aleksinac (b) 15 Aleksinac (c)

6.087 5.712 5.858 3.857 3.733 3.689 8.732 8.528 7.647 5.751 5.733 5.585 4.948 4.362 4.313

4.937 4.7ll 4.801 2.824 2.835 2.468 8.810 8.644 7.685 4.251 4.672 4.388 6.001 5.705 5.734

5.1 5.4 5.3 9.1 9.4 9.7 3.4 3.3 3.8 5.5 5.5 5.7 6.0 6.3 6.4

19.1 19.7 18.6 38.6 36.9 43.0 8.6 8.6 10.3 21.7 20.2 22.7 13.6 13.9 14.5

Bitumens 17 Torbanite (a) 18 Kimmeridge (a) 19 Colorado (a) 20 Aleksinac (a) 21 (Asphaltenes)

2.449 6.655 2.573 2.213 5.949

2.154 6.484 3.242 2.321 5.485

14.0 6.0 13.1 15.0 5.8

45.3 13.8 35.4 48.0 13.6

No.

Shale

*(a), (b) and (c) refers to the unsieved, the -0.050 + 0.040 mm and the -0.040 mm samples, respectively. OG 6 : I / h - M *

386

PETAR A. PFENDT

o

CH> -

,

o

I

CH CHz CH CH z CH --CH 2 ~ C H 2 I /\/X/\/\/X/X/ O=C--NH--CH 2 CH2 CH2 CH 2 CH2 CH2 CH2 IS

Fig. 1. Model(A): Coloradoshalekerogenstructure,afterYen (1976).

H~O~~--(CH2)2CH3

Kerogens have the same order in the Van Krevelen diagram (Fig. 7) as one goes from higher to lower O/C ratios. The benzene-soluble bitumens are less reactive towards bromine than the corresponding kerogens and the order of the decrease of their reactivity is not the same:

H3C( H2C )IO ~ X ~ / )

o

Asphaltenes> Kimmeridge ~>Colorado ~>Torbanite >Aleksinac

H3C-~

Fig. 2. Model (B): algal kerogen model (Combaz, 1980).

gated substance occupies points to the chemical similarity of a specific kerogen with one of the structural models. DISCUSSION

The C/Br vs H/HBr diagram on Fig. 6 as one goes diagonally from the beginning of the coordinating system, indicates that the number of reactive sites towards bromine decreases in the kerogens of different types according to the following sequence: Kimmeridge~>Aleksinac >Kukersite >Colorado [I

II

[I-I

~>Torbanite !

I

The investigated samples of the Australian Torbanite occupies a position to the left from the bromination line of the Colorado kerogen model (A), which points to structures that consume more bromine than this model, but with the liberation of a lesser amount of hydrogen bromide, i.e. the Torbanite kerogen is more "unsaturated", or it contains less structures that react by substitution or oxidation than the Colorado kerogen model (A) (Fig. 1). The Torbanite kerogen occupies a separate position also in the Van Krevelen diagram, mainly as a consequence of its low O/C ratio. Closest to the Torbanite kerogen in the Van Krevelen diagram is the Colorado kerogen, and according to their position in this diagram both kerogens belong to type I. The Colorado kerogen is richer in oxygen although it has approximately the same H/C ratio as the Torbanite kerogen. In the C/Br vs H/HBr diagram their differences are reflected in considerably higher reactivity of the Colorado kerogen towards bromine and in higher content of

387

Nature of kerogens based on their Br activities

~ ~

= 0 ~ / OH

Fig. 3. Model (C): type II kerogen, after Tissot el al. (Oberlin et al., 198{)).

OH o===(

..)---c----o---{

X "/

~

v

COOH

~6Hl105

I

0

CH2

I

Hz

)---c..

OCH3

D

.-X

OH I

OH ,)----- c - - o ----K

H

H2

)~c..

.g

(~I

H

I

CH2

,)---c--o--{,

)===o

k~W

~,,

I

CO-- NH - - CsHIBO3N E

CzH5 CH3 H 3 C ~ c H 3

OH (CH2)2CH3 H

3 N

HO

C~ 0

v

C ~~H2II4CH3 CH 3

C

~

(CH215-S- (CH2)5 - - )

~

~ , ~HZ)z__CH3

~OH H3C/~

~H2

0

s

Z

Fig. 4. Model (D): humic acid model of Dragunov (Cooper and Murchison, 1969); Model (E): kerogen liptinic (Combaz, 1980); Model (F): asphaltenes, after Yen (Vandenbroucke, 1980).

388

PETAR A. PFENDT

/H OH H

OH

0

H2

0 I

H

H2

H H2 H2

~

I/

0

o

T 11 H2C~c~(;H2 H2 ,, J. H2C-,

HOOCH3 f) %o

H

(0H2)2 OH 3

Fig. 5. Model (G): structure of coal vitrinite of Given (I96()); Model (H): lignohumic kerogen (Combaz, ]980),

structures that react with bromine by substitution or oxidation, as well as in greater similarity of the Colorado kerogen with its structural model (A). The Kukersite kerogen shows considerable chemical similarity with the Colorado kerogen. In the C/Br vs H/HBr diagram it occupies a region very close to the bromination line of the Colorado kerogen model (A) but to the right of this line, and it is somewhat more reactive towards bromine in the sense of substitution or oxidation. According to its position it ought to be similar to the model of the Colorado kerogen, but more reactive and more unsaturated than the model of algal kerogen (B) (Fig. 2). The Kukersite kerogen follows the Colorado

,~.

H C2

O~H

kerogen in the Van Krevelen diagram also. However, according to its position it is closer to type II than type I kerogen. Therefore, the C/Br vs H/HBr diagram allows consideration of additional details about the nature of this intermediate type of kerogen. This conclusion is reached also by consideration of the Kimmeridge kerogen. According to its position in the Van Krevelen diagram this kerogen belongs distinctly to type II. The C/Br vs H/HBr diagram indicates, besides belonging of the Kimmeridge kerogen to type I1, model (C), that this kerogen is the most reactive one towards bromine among all examined kerogens and that by this, as well as by its general chemical nature, it considerably differs from the kerogen of the Aleksinac shale which also belongs to type II. The kerogen of the Aleksinac shale occupies a position near to the bromination line of the liptinite kerogen model (E) and the asphaltene model (F) but to the right. This indicates that in this kerogen the ratio of structures which react by substitution or oxidation to the total number of structures which consume bromine is greater than in the previously mentioned models. The asphaltenes in the C/Br vs H/HBr diagram are located on the bromination line of their structural model (F). In their vicinity is the Aleksinac kerogen and the benzene bitumen of the Kimmeridge shale which points to a certain chemical similarity of these three substances. The Aleksinac kerogen is somewhat more saturated, and the Kimmeridge bitumen is somewhat more unsaturated than asphaltenes.

389

Nature of kerogens based on their Br activities Table 4. The structural models of ancient sediment organic substances for which the bromination lines were calculated Bromine HBr consumption liberation (mol mol -~)

Sign

Model

C/Br

H/HBr

a*

A

Colorado kerogen C2~3H415OI3N3S6 (Yen, 1976)

92

78

1.429

5.321

3.724

B

Algal kerogen C4~HxIO3N (Combaz, 1980)

20

20

1.225

4.050

3.306

C

Type II kerogen C563H675031 N4S4v (Tissot-Espitalid-Durand-Vandenbroucke) (Oberlin etal., 1980)

133

119

2.117

5.672

2.679

D

Humic acid Cs,H,,)O: 1N4 (Dragunov) (Cooper, Murchison, 1969)

26

25

1.115

2.760

2.475

E

Kerogen liptinic C~,,~H~sOvN (Combaz. 1980)

21

22

1.643

3.864

2.352

F

Asphaltenes (oil) C74H,3ONS2 (Yen. 1976)

14

15

2.643

6.200

2.346

20

19

2.575

4.105

1.594

13

14

1.769

2.786

1.575

(Vandenbroucke, 1980) G

Vitrinite

C I, )3H7~O I I ) N 2 (Given, 1960) H

Kerogen lignohumic C u~H>O~,N (Combaz, 1980)

*a = slope of the bromination line H/HBr = a(C/Br).

I 45

40

Shale Kukersite

Ker

Bit

•

V

Tar bonOe

~

Colorado

•

o

Aleksinac

1

z~

Shele

( Asphattene

Ker

Bit.

Kukersite

v

7

Torbanite

~

(~

-l-

-c-

Colorado

•

o

Aleksinac

•

,',

--

X

Kimmeridge

35 ,P

£,F

3O

(A s p h a l t e n e s )

,\/

t

17 ~1o

16

0

/,

"~.~'~ ~ ~

2O 15

°

°

•

•

A

14

# ,/

13 12 11

5

10 0

L _ 2

_L 4

0 05 6

8

if0

12

14

IG

C 8r

Fig. 6. The C/Br vs H/HBr diagram (see also Table 4).

010

0.15

0 20

0 C

Fig. 7. The Van Krevelen diagram.

025

390

PETARA. PFENDT

In Advances in Organic Geochemistry 1968 (Edited by Schenck P. A. and Havenaar I.), pp. 85-129. Pergamon (1) By linking the data of elemental analysis of the Press, Oxford. organic substances of ancient sediments (i.e. Combaz A. 11980) Les k6rog6nes vus au microscope. In Kerogen--lnsoluble Organic Matter from Sedimentary kerogens, benzene-soluble bitumens) with the Rocks (Edited by Durand B.), pp. 55-111. t~dition amount of bromine that these substances under Technip, Paris. certain conditions may consume and with the amount Cooper B. S. and Murchison D. G. (1969) Organic geochemistry of coal. In Organic Geochemistry (Edited by of hydrogen bromide which is consequently liberEglinton G. and Murphy M. T. J.), p. 714. Springerated, the C/Br and H/HBr ratios were obtained, Verlag, Berlin, which present a basis for a more detailed character- Costa Nero C., Maqaira A. M. P., Pinto R. C. P., ization of the general chemical nature of the subNakayama H. T. and Cardoso J. M. 11980) New analytical approach to organic geochemistry: solid phase funcstances. tional group extraction from bitumens and functional (2) Useful indicators for characterizing the chegroup analysis for kerogens. In Advances in Organic mical nature of the organic substance of ancient Geochemistry •979 (Edited by Douglas A. G. and sediments were found to be (a) the distance of the Maxwell J, R.), pp. 24%263. Pergamon Press, Oxford. position of an investigated substance from the begin- Given P. H. (1960) The distribution of hydrogen in coals and its relation to coal structure. Fuel 39, 147-153. ning of the coordinating system of the C/Br vs H/HBr diagram and (b) the region which the investigated Jovanovi6 S. Lj. and Vitorovi6 D. 11952) Contribution to the study of oil shales from Aleksinac. Bull. Soc. chim, substance occupies between two bromination lines Belgrade 17, 347-360. which are obtained by theoretical consideration of Murphy R. C., Biemann K., Djuri6i6 M. and Vitorovi6 D, (1971) Organic acids obtained by alkaline permanganate the behaviour of known structural models for ancient oxidation of kerogen from the Green River (Colorado) organic substances towards bromine. Shale. Geochim. Cosmochim. Acta 35, 1201-1207. (3) The order of kerogens in the C/Br vs H/HBr Oberlin A., Boulmier J. L. and Villey M. 1198/)) Electron diagram, according to the decrease in the reactivity microscopic study of kerogen microtexture. Selected towards bromine, corresponds to their sequence in criteria for determining the evolution path and evolution stage of kerogen. In Kerogem--lnsoluble Organic Matter the Van Krevelen diagram as one goes from higher to from Sedimentary Rocks (Edited by Durand B.), pp. lower O/C ratios (i.e. Kimmeridge, Aleksinac, 191-241. t~dition Technip, Paris. Kukersite, Colorado, Torbanite). Patai S. (Ed.) (1973) The Chemistry of the Carbon-Halogen (4) The position of a kerogen in the C/Br vs Bond, Parts I and II. John Wiley, Chichester. H/HBr diagram enables to distinguish the chemical Pfendt P. A. (1975) Ein Studium der chemischen Natur des Aleksinacer Oelschieferkerogens auf Grund Bronature of kerogens which, according to their position mierungsreaktionen. Dissertation, University of Belin the Van Krevelen diagram, belong to the same grade. type of kerogen (e.g. the kerogens of Australian Pfendt P. A. and Vitorovi6 D. 11973) Untersuchung der Torbanite and of the Colorado shale). Furthermore, Struktur des Aleksinacer Oelschieferkerogens mittels modifizierter Jodzahlmethoden. II. Der Einfluss des it enables also to better explain the chemical nature Bromwasserstoffs. ErdOl Kohle 26, 143-148. of intermediate types of kerogen (e.g. the Estonian Roedig A., Kreutzkamp N., Meerwein H. and Stroh R. Kukersite kerogen). (1960) Methoden zur Herstellung und Umwandlung von (5) The asphaltenes from oil have a structure very Halogenverbindungen. In Methoden der Organischen Chemie (Houben-Weyl) (Edited by Miiller E.), Band similar to their structural model (Yen, 1974a). The V/4, pp. 13-516. Georg Thieme Verlag, Stuttgart. benzene-soluble bitumen of the Kimmeridge shale Tissot B. P. and Welte D, H. (1978) Petroleum Formation and the kerogen of the Aleksinac shale might have a and Occurrence. p. 538. Springer-Verlag, Berlin. somewhat similar chemical structure. Vandenbroucke M. (1980) Structure of kerogens as seen by (6) The Colorado kerogen (type I) is poorer in investigations on soluble extracts. In Kerogen--lnsoluble Organic Matter .from Sedimentary Rocks (Edited by structures that react by substitution or oxidation Durand B.), pp. 415-443. Editions Technip, Paris. (tertiary CH, aromatic nuclei, alcoholic, phenolic Vitorovi6 D. K. and Pfendt P. A. (1974) Effect of bromine and ketonic structures), than its structural model on Aleksinac Shale kerogen--source of data for better (Yen, 1974). understanding of its chemical nature. An. Acad. Brasil. Ci(nc. 46, 49-55. Vitorovi6 D. K., Krsmanovi6V. D. and Pfendt P. A. 11977) Acknowledgements--Financial support by the Research Eine Untersuchung der Struktur des Aleksinacer OelFund of the S.R. Serbia (Yugoslavia) is gratefully acknowschieferkerogens mittels verschiedener chemischer ledged. Methoden. In Advances in Organic Geochemistry 1975 (Edited by Campos R. and Goni J.), pp. 71!7-734. REFERENCES ENADIMSA, Madrid. Burlingame A. L., Haug P. A,, Schnoes H. K. and Simoneit Yen T. F. (1976) Structural aspects of organic components in oil shales. In Oil Shale (Edited by Yen T. F. and B. R. (1969) Fatty acids derived from the Green River Chilingarian G. V.), pp. 129-148. Elsevier, Amsterdam. Formation oil shale by extraction and oxidation-- review. CONCLUSIONS