kerogens from source rocks of the Gandhar Field, Cambay Basin, India

Org. Geochem. Vol. 21, No. 3/4, pp. 383-392, 1994 Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0146-6380/94 $7.00 + 0.00

Pergamon

Pyrolysis-gas chromatography of asphaltenes/kerogens from source rocks of the Gandhar Field, Cambay Basin, India A. K. GARG1and R. P. PHILP2 ~Geochemistry Division, KDM Institute of Petroleum Exploration, Oil and Natural Gas Commission, Dehradun 248195, India and 2School of Geology and Geophysics, University of Oklahoma, Norman, OK 73019, U.S.A. Abstract--Pyrolysis-gaschromatography of rocks from three exploratory wells in the Gandhar area of the Cambay Basin, India, reveals that the organic matter is dominated by input from higher land plants. The pyrograms of asphaltenes and kerogens demonstrate that the Hazad and Cambay Shale were deposited in different environments with the former being an overall regressive deltaic environment and the latter a marine transgressive sequence. Studies of TOC (values range from 1 to 2.6%), Rock-Eval (HI values range from 70 to 183), pyrolysis-gas chromatography, vitrinite reflectance (Ro range from 0.4 to 0.8), bitumen extracts and isotopic ratios demonstrate that both Hazad and upper Cambay Shale can act as effective source rocks wherever they are thermally mature. Key words--source rock, asphaltene, kerogen, pyrolysis-gas chromatography, Gandhar, Cambay Basin,

India INTRODUCTION

Cambay Basin is a rift basin and an inland extension of the large offshore basin located on the northwest margin of the Indian Platform. The geology and stratigraphy of Cambay Basin have been extensively studied and reported by Raju (1968), Raju and Srinivasan (1983), and Chandra and Chowdhary (1969). The basin is subdivided into four tectonic structural blocks: (1) Ahmedabad; (2) Cambay-Tarapur; (3) Jambusar Broach; and (4) Narmada (Fig. 1). Hydrocarbon accumulations in these blocks have been discovered in Eocene to Miocene reservoirs having shale cap rocks of Eocene to Miocene age. The Cambay Shale sequences have long been recognized as the major source rocks for the large oil and gas accumulations in the Cambay Basin by Chandra and Chowdhary (1969), Chandra et al. (1982), Garg et al. (1985, 1987) and Philp and Garg (1991). In the Broach depression, the Cambay Shale has undergone deep subsidence and is thought to have generated hydrocarbons in large quantities as reported by Yalcin et al. (1987) through 3-D computer aided basin modelling. In the rising north-western flank of the Broach depression is the Gandhar field, which contains large hydrocarbon accumulations. The Broach depression is 50 km long and 16 km wide covering an area of 800 km 2 located partly on land and partly on the shelf area adjoining the Gulf of Cambay. Tertiary and Quarternary sequences of the order of 5000 m are expected to lie unconformably over the Deccan Trap. The Hazad Member of Anklesvar Formation is the main target of exploration. The Hazad reservoir sandstones are sub-divided into sub-units (GS-1 to GS-12), and the total thickness of Hazad Member varies between 383

180-200 m. The reservoir sands are inferred to pinchout towards the west and north in the adjoining Gulf and Jumbusar area. The Gandhar field has been divided into three sectors: North Gandhar, North-East Gandhar and South Gandhar. The present study was confined to the South Gandhar sector using the samples from three exploratory wells A, B and C (Fig. 1). Samples from these wells ranging in depth from 1500 to 3200m at 5-m intervals were first screened using Rock-Eval pyrolysis. Pyrolysis-gas chromatography (Py-GC) studies were subsequently performed on selected samples to determine the nature of source organic matter. Hydrocarbon generation potential of the samples was evaluated using various geochemical techniques, especially Py~3C. Py--GC is now being used routinely to characterize petroleum source rocks, kerogens, asphaltenes, coals and other organic rich materials from diverse sources for better implementing petroleum exploration strategies (Larter, 1978, 1985; Larter and Douglas, 1980; Van Graas et al., 1981; Van de Meent et al., 1980; Solli and Leplat, 1986; Vandenbroucke et al., 1988 Rose et al., 1992). P y - G C studies on both kerogen and asphaltenes were performed to obtain a more detailed insight on the kerogen structures. Behar and Pelet (1985) suggested that kerogens and asphaltenes are genetically related, possibly originating from the same precursors. Striking similarities between asphaltenes and kerogen structures have been observed in Py--GC studies (Bandurski, 1982; Behar and Pelet, 1984, 1985; Larter and Douglas, 1980; Aref'yev et al., 1980; Philp and Gilbert, 1987; Philp and Bakel, 1988). A number of parameters has been developed for the kerogen characterization. In the present work a number of Py~3C parameters

384

A. K, GARGand R. P. PHILP

[e.g. n-alkene/n-alkane; toluene/nCj0, phenol/nCL2, C6-Cj3/(toluene + phenol + xylene); (mono + disubstitutednaphthalenes)/C3-alkylbenzene and (m + p ) xylene/n-octene] have been utilized to evaluate the nature and hydrocarbon generation potential of the source rock kerogens from the Gandhar field. The significance of these parameters and their application to kerogen characterization has been described previously by Larter and Senftte (1985), Oygard et al. (1988), and Christie et al. (1989). EXPERIMENTAL

Six core/cutting samples from each of the three exploratory wells A, B and C in the depth range of 2550-3175 m, covering Eocene-Paleocene sequences, in Hazad/Cambay shale formations were studied. Crushed whole rock samples were extracted with methylene dichloride/methanol (1:1) for 48h by Soxhlet extraction prior to kerogen isolation using the H C L / H F procedure described by Saxby (1976). The isolation of the asphaltenes was undertaken in a round bottom flask using 100 mg of rock extract in methylene dichloride. Excess solvent was evaporated using a rotary evaporator and then excess n-pentane (40 times the amount of rock extract) was added and left in a refrigerator overnight. The asphaltenes precipitated as a dark brown solid which was filtered on a sintered glass funnel and was washed thoroughly with n-pentane four to five times in order to remove

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adsorbed and/or co-precipitated material. The aso phaltenes were stored at 0°C in a refrigerator prior to performing Py43C of the asphaltenes and their corresponding kerogens using a Chemical Data System (CDS) ribbon probe/Pyroprobe 122 with extended temperature programming capabilities interfaced to a Varian 3300 gas chromatograph. Milligram amounts of kerogens were loaded individually into a quartz glass tube, which was then plugged at each end with quartz wool. The asphaltenes were pyrolysed using the ribbon probe of the CDS Pyroprobe 122, at a temperature setting of 800"C, corresponding to pyrolysis of 610~C. for 20 s. The pyrolysates were rapidly removed from the heated interface (30@C) by a stream of helium onto a 30 m x 0.25 mrn i.d., fused silica DB-5 (1.0 pm film thickness; J & W Scientific) capillary column in a Varian 3300 gas chromatograph equipped with a split/splitless injector operated in the splitless mode. The column temperature was held at 25°C for 4 rain. and raised to 300°C at the rate of 4 ~C/min. The major peaks in the pyrolysates were identified by comparison of their retention time with those of authentic standards. RESULTS AND DISCUSSION

The three exploratory wells, A, B and C, of Gandhar field in Cambay Basin, India from which the samples were obtained are shown in Fig. 1.

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Organic carbon and Rock-Eval analysis were performed on samples from a depth range of 15003200 m at 5 m intervals. Geochemical logs were prepared (not shown here), and based on these results only Hazad and Cambay shales could be effective source rocks. Six core/cutting samples in the depth interval of 2550-3175 m from these two sequences were selected from each well for the present studies; some of the geochemical parameters of these samples are given in Table 1. In the Middle Eocene Hazad shale, TOC values vary from 1 to 2.5% and the extractable organic matter (EOM) values from 0.2 to 0.5%. The percentage extractable organic matter/Corg ratio ranges from 9 to 20.8 indicating very good source rock potential. The hydrogen indices (HI) vary from 88 to 183 mg HC/g TOC. Plots of Tmax vs HI show that most samples can be classified as Type III kerogens. Tmax values between 430-446°C and vitrinite reflectance values from 0.44 to 0.65% Ro indicate that the organic matter is at the threshold of hydrocarbon generation. In the Lower Eocene-Paleocene Cambay Shale Formation, TOC varies from 1.5 to 2.3% and the extractable organic matter ranges from 0.2 to 0.3%. The percentage extractable organic matter/Corg ratio varies from 8.6 to 12.2% and indicates that the sequence has very good source rock potential. The HI values vary from 66 to 143 mg HC/g TOC, showing characteristics of Type III kerogens (Table 1). Traax values range from 435 to 450°C, and vitrinite reflectance values between 0.61-0.80% R o, illustrating the maturity of these sequences. The bitumen content of these samples, % EOM, and % EOM/TOC (Table 1) suggest that these bitumens are syngenetic in nature. Stable carbon isotopic values for various fractions of the bitumens from these samples (Fig. 2) suggest a non-marine origin for the organic matter responsible for the bitumen extracts of these samples from the Gandhar field (Sofer, 1984).

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The asphaltenes and kerogens were analysed under identical Py-GC conditions. Pyrograms of the asphaltenes and kerogens from well A at the depth 2997 m of Hazad Shale and 3175 m of Cambay Shale are shown in Fig. 3. The pyrogram of the asphaltenes is dominated by an alkene and alkane homologous series ranging from C6 to C29 with an unresolved "naphthenic hump" whereas the kerogen pyrogram is dominated by alkene/alkane doublets in the C6-C~3 range. COmparison of the asphaltene pyrogram with that of corresponding kerogen reveals some significant differences. In particular, kerogen pyrograms show abundant aromatic xylenes and phenols, while asphaltene pyrograms show relatively lower abundance of these aromatic compounds. Relatively higher proportions of isoprenoids (especially prist-lene), methyl naphthalenes, dimethylnapthalenes and

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long chain hydrocarbons (C14-~229) are observed in the pyrograms of the asphaltenes. Pyrograms of the asphaltenes and their corresponding kerogens from well B at depth 2950 m of Hazad Shale and 3150 m of Cambay Shale are shown in Fig. 4. The asphaltene pyrograms of these sedimentary sequences show a distribution dominated by long-chain alkanes extending to C32 and containing less aromatics and a relatively higher proportion of isoprenoids. The pyrograms of the kerogens are dominated by alkenes/alkanes in the C6-C13 range with relative high proportions of aromatic hydrocarbons and phenols. As the level of maturity increases, an increase in the relative concentration of normal hydrocarbons over isoprenoids and other hydrocarbons (phenolic and aromatic compounds) occurs in the pyrolysates of kerogens from a depth of 2950-3150 m. In kerogens, a similar maturation trend with increasing aliphatic character of the pyrolysates has been reported by Durand (1980), Van de Meent et al. (1980) Van Graas et al. (1981), Philp and Gilbert (1984, 1985, 1986, 1987), and Solli and Leplat (1986). An artificial maturation study of kerogens also showed an increase in the aliphatic nature of the pyrolysates with increasing heating time and temperature (Eglinton et al., 1988; Vallejos et al., 1989). The increase in normal hydrocarbons with increasing maturity is due to the preferential loss of heteroatomic and branched chain materials during maturation (Eglinton and Douglas 1988; Huizinga et al., 1988; Zhiwet and Xluli, 1987; Peters et al., 1990). The observations described above suggest that during thermal evolution, kerogens and asphaltenes

from the same source rock follow similar evolutionary lines. The effect of organic facies in the pyrolysates can be better understood by coupling the pyrograms of kerogen and asphaltene together, particularly at the threshold of hydrocarbon generation stage. The pyrograms of the asphaltenes and kerogens from well C and isolated from rocks at 2950 m in the Hazad Shale and 3150 m in the Cambay Shale are shown in Fig. 5. A comparison of the well C asphaltene with that of the corresponding kerogen, shows a similar trend to those observed for the kerogen/asphaltene samples of wells A and B. The asphaltene pyrolysates have higher relative proportions of long alkyl chains compared to those of the corresponding kerogens. This might be due to less cross-linking of alkyl chains m the asphaltene structure, which would result in ~ higher relative proportion of long chains in the asphaltene structure compared to that observed in the corresponding kerogen. The pyrograms of kerogens and asphaltenes, respectively, from the different wells are similar from a qualitative viewpoint but differ from each other on a quantitative scale. Visual comparisons do not afford quantitative estimates of the degree of correspondence between different pyrograms of kerogen and asphaltene of Hazad and Cambay shale. In order to investigate the environment of deposition and to ascertain the relative contribution of aliphatic and aromatic species in Hazad Shale and Cambay Shale, an attempt was made to utilise semi-quantitative indices listed in Table 2. The ratio of (mono + disubstituted-naphthalenes)/ C3-alkyl benzene as well as the ratio of C6--C~3 (toluene + phenol + xylene) in the pyrolysates of asphaltene and kerogens of Hazad and Cambay Shale are in the same range (Table 2). This correspondence would indicate similarities in the types of organic matter input in Hazad Shale (0.7 27.81) and Cambay Shale (0.75 17.96). Latter (1985) previously reported values lbr these ratios of 0.67 for Type II kerogens and higher values for Type Ili kerogens and coals (I.24-3.09). Based on this observation it can be proposed that the Hazad and Cambay Shale kerogens are Type III kerogens, which is supported by the HI/OI plots as well as the higher wax content of the extracts. The ratio of n-alkene to n-alkane in the C~---C~3 carbon number range was determined for both the kerogens and asphaltenes of Hazad Shale and Cambay Shale formations (Table 2). In both the kerogen and asphaltene pyrograms the relative proportion of n-alkene to n-alkane is higher in the Cambay Shale than in the Hazad Shale, possibly suggesting a small difference in the nature of the original organic source materials. Such an observation is supported by the fact that in the kerogen pyrogram of Hazad Shale the phenol/nC~: ratio is higher (0.5-1.8) than that for the Cambay Shale (0.3--0.9), demonstrating that Hazad Shale kerogens have more terrigenous affinity corn-

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kerogen pyrolysates the relative proportion of xylene/n-octene is higher for the more aromatic in Hazad Shale (1.0-5.5) than the Cambay Shale (0.9-3.8). Values of 1.98-5.47 were reported for coals and 0.83-2.84 for kerogens of Type III and

pared to the Cambay Shale kerogens. Differences in organic matter composition of Hazad Shale and Cambay Shale are also reflected in the xylene/noctene ratio, which can be used as an indicator of the aromatic/aliphatic nature of the kerogens. In the (a)

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In order to differentiate between Hazad and Cambay Shale organic facies, kerogen pyrolysates (m + p

xylene, n-octene and phenols) were plotted on a triangular diagram (Larter, 1984) (Fig. 6). The Hazad and Cambay Shale fall into two distinctly different groups with kerogens of Hazad shale yielding relatively more (m + p)-xylene as compared to Cambay Shale kerogen. Unpublished geological studies

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Fig. 6. Ternary diagram showing distribution of n-octene, (m +p)-xylene and phenol from kerogen pyrograms of key wells of Gandhar field. suggest that the Hazad Shale was deposited in an overall regressive deltatic environment whereas the Cambay Shale was deposited during a transgressive phase. Pasley et al. (1991) observed that the transgressive shale kerogens in San Juan Basin of New Mexico yield more aliphatic hydrocarbons, whereas regressive shale kerogens yield more aromatic hydrocarbons on pyrolysis. The maturity parameters, Ro and Tmax,summarized in Table 1 suggest that for the most part these samples of Cambay and Hazad shale are at the early stages of catagenesis. However, TOC and bitumen content as well as Rock-Eval and pyrolysis data suggest that equivalent rocks may have acted as effective source rocks in the deeper part of the Broach depression where these sequences are deeply buried and have reached peak hydrocarbon generation stage. CONCLUSIONS

In the Gandhar field, the Hazad and Cambay Shales are source rocks, both of these intervals contain mainly higher land plant input, and the organic matter is of Type III. The P y - G C technique has been used to reliably and accurately evaluate the hydrocarbon source potential of these sequences. The study indicates that when pyrograms of kerogens and their corresponding asphaltenes are used together, they provide a better understanding of the type of organic matter, especially at the threshold of hydrocarbon generation stage. The kerogen pyrograms of Hazad Shale contain a significant con-

tent of xylenes, toluenes and phenols, illustrating the more aromatic nature of this shale compared to the Cambay Shale. Cambay Shale is a marine transgressive sequence whereas the Hazad Shale was deposited in an overall regressive deltaic environment. The samples studied are still at the early catagenetic stage, but might act as effective source rocks wherever they have subsided to greater depth and are more mature. Acknowledgements--We are indebted to the Oil & Natural

Gas Commission, Dehradun, India, for granting AKG study leave, providing samples for the study and for according permission to publish this paper. We express our sincere gratitude to Mr Kuldeep Chandra, Director, IMD, ONGC, Dehradun for his valuable suggestions incorporated in the manuscript. We thank Mr K. N. Misra Deputy General Manager ONGC, Dehradun for helpful review of the manuscript. We are grateful to Dr V. Banerjie, Dr C. S. Mishra and Mr U. Samanta, Geochemistry Division, KDMIPE, ONGC, Dehradun, India for lively discussions during the interpretation of the results. Technical support provided by Dr Allen Bakel, University of Oklahoma, Norman, U.S.A. is gratefully acknowledged. REFERENCES

Aref'Yev O. A., Makushina V. M. and Petrov A. A. (1980) Asphaltenes as indicators of geochemical history of crude oils. lzv. Akad. Nauk. SSSR Ser. Geol. 4, 124-130 (in Russian).

Bandurski E. (1982) Structural similarities between oil generating kerogens and petroleum asphaltenes. Energy Sources 6, 47-67. Behar F. and Pelet R. (1984) Asphaltene characterization by pyrolysis and chromatography. J. Anal. Appl. Pyrol. 7, 121-135. Behar F. and Pelet R. (1985) Pyrolysis-gaschromatography

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A.K. GARG and R. P, PHILP

applied to organic geochemistry. Structural similarities between kerogens and asphaltenes and related rock extracts and oils. J. Anal. Appl. PyroL 8, 173487. Chandra P. K. and Chawdhary L. R. (1969) Stratigraphy of Cambay Basin. Bull. Oil Nat. Gas Commiss. 6, 37-50. Chandra K., Kumar R. K., Balan K. C., Prakash C., Datta G. C., Das S. P. and Mali M. R. (1982) Chemistry and genesis of Cambay Basin crudes, Phase-l. A study of gross compositional characteristics and classification of crudes. A report: S&T-9 KDMIPE ONGC, pp. 6 186 (Unpublished). Christie A. A,, Hopland A. L., Barth I . and Kvalhehn O. M, (1989) Quantitative determination of thermal maturity in sedimentary organic matter by diffuse reflectance infra-red spectroscopy of asphaltenes. Org. Geochem. 14, 77 +81. Durand B. (1980) Insoluble organic matter from sedimentary rocks. In Kerogen (Edited by Durand B.), pp. 133 14l. Technip, Paris. Eglinton T. 1. and Douglas A. G. (1988l Quantitative study of biomarker hydrocarbons released from kerogens during hydrous pyrolysis. Energy & Fuels 2, 81 88. Eglinton T. 1.. Philp R. P. and Rowland S. J. (1988) Flash pyrolysis of artificially matured kerogens from the Kimmeridge clay, U.K. Org. Geochem. 12, 33 42. Garg A. K., Chawla B. R. and Misra K. N. (1987) Source rock evaluation of the sedimentary sequences of a well in Cambay Basin India. In Abstracts of the AAPG Symposium on Application of Geochemistry in Petroleum Exploration, Denver, Colo. Garg A. K., Chawla B. R., Shukla R K. and Sharma B. N. (1985) Geochemistry of organic matter of the key wells of Cambay Basin. ONGC KDMIPE Report, p. 24, Huizinga B. J,, Aizenshtat Z. A. and Peters K. E. (1988) Programmed pyrolysis-gas chromatography of artificially matured Green River kerogen. Energy & Fuels 2, 74 81. Larter S. R (1978) A geochemical study of kerogen and related materials. Ph.D. thesis. University of Newcastleupon-Tyne Larter S. R. (t984) Application of analytical pyrolysis techniques to kerogen characterization of fossil fuel exploration/exploitation. In Analytical Pyrolysis (Edited by Voorkees K. E.), Vol. 1I, pp. 212 272. Butterworths, London. Larter S. R (1985) Integrated kerogen typing of the recognition and quantitative assessment of petroleum source rocks. In Petroleum Geochemistry in Exploration o f the Norwegian She![~ pp. 269 286. Norwegian Petroleum Society, Graham & Trotman, London. Larter S. R and Douglas A. G. (1980) A pyrolysis-gas chromatography method for kerogen typing. In Advances in Organic Geochemistry 1979 (Edited by Douglas A G. and Maxwell J. R.), pp. 212 275. Butterworths, London. Larter S. R. and Senftle J. T. (1985) Improved kerogen typing lbr petroleum source rock analysis. Nature 318, 277-280. Oygard K., Larter S. and Senftle J. (1988) The control of maturity and kerogen type on quantitative analytical pyrolysis data. In Advances in Organic Geochemistry 1987 (Edited by Mattavelli L. and Novelli L.). Org. Geochem. 13, 1153 1162. Pergamon Press, Oxford Pasley M. A.. Gregory W. A. and Hart G. I-. (1991) Organic matter variations in transgressive and regressive shales. Org. Geoehem. 17, 483-509. Peters K. E., Moldowan J. M. and Sundararaman P. (1990) Effects of hydrous pyrolysis on biomarker thermal maturity parameters: Monterey phosphatic and siliceous members. Org. Geochem. 15, 249-265. Philp R. P. and Bakel A. (1988) Heteroatomic compounds produced by pyrolysis of asphaltenes. Energy & Fuel 2, 59~4, Philp R. P, and Garg A. K. (1991) Characterization of some

sedimentary sequences from Cambay Basin, India by pyrolysis-GC. J. Southeast Asian Earth Sci. 5, 31-38. Philp R. P. and Gilbert T. D. (1984) Characterization of petroleum source rocks and shales by pyrolysis-gas chromatography-mass spectrometry multiple ion detection. In Advances in Organic Geochemistry 1983 (Edited by Schenck P. A., de Leeuw .L W. and Lijmbach G. W. M.). Org. Geochem. 6, 489-503. Pergamon Press, Oxford. Philp R. P. and Gilbert T D. (1985) Source rock and asphaltene biomarker characterization by pyrolysis-gas chromatography multiple ion detection. Geochim. Cosmochim. Acta 49, 1421 1432. Philp R. P. and Gilbert T. D. (1986) Biomarker distribution in Australian oils predominantly derived from terrigenous source material. In A&,anees in Organic Geochemistry 1985 (Edited by Leythaeuser D. and Rullk6tter J.). Org. Geochem. 10, 7384. Pergamon Press, Oxford. Philp R. P. and Gilbert T. D. (1987) A review of biomarkers in kerogens as determined by pyrolysis-GC and pyrolysis GCMS..L Anal. Appl. Pyrol. II, 93 108. Raju A T R. (1968) Geological evolution of Assam and Cambay Tertiary Basins of India. Am. Assoc. Pet, Geol. Bull. 52, 2422--2437. Raju A. T. R and Srinivasan S. (1983) More hydrocarbons from well explored Cambay Basin. Pet. Asia J. 6, 25 35 Rose H. R., Smith D. R., Hanna J. V., Palmisano A. J. and Wilson M. A. (1992) ( omparison of the effect of minerals on aromatization reactions during kerogen pyrolysis. Fuel 71, 355 36(I. Saxby T. D (1976) ( ilemica~ separation and characterlz~ ation of kerogen and oil shale. In Oil Shale (Edited by Yen T. F. and Chilingarian G. Vt. Dev. Pet. Sci. 6, 102 122. Elsevier, Amsterdam Sofer Z. (1984) Stable carbon isotope composition of crude oils: application to source depositional environments and petroleum alteration. Am. Assoc. Pet. Geol. Bull. 68, 31 49. Solli H, and Leplat P. I 1980) Pyrolysis gas chromatography of asphaltenes and kerogens from source rocks and coals-, a comparative structural study. In Advances in Organic Geochemistr~ 1985 (Edited by Leythaeuser D. and Rullk6tter J.). Org, Geochem 10, 313 -329. Pergamon Press, Oxford. Vallejos C., Talukdar S. and Philp R. P. (1989) The distribution of organosulphur compounds in artificial!y matured rocks and kerogens of the La Luna Formation, Maraeaibo Basin, Venezuela. Energy & Fuels 3, 366 369. Vandenbroucke M., Behat F. and Espitalie J. (1988) Characterization of sedimentary organic matter by preparative pyrolysis: comparison with Rock-Eval pyrolysis and pyrolysis-gas chromatography techniques. Energy & Fuels 2, 252 258. Van Graas G., De Leeu~ J. W.. Schenck P. A. and Haverkamp J. (1981) Kerogen of Toarcian shale of the Paris Basin. A study of its maturation by flash pyrolysis techniques. Geochim. ('osmochml. Acta 45, 2465 2474. Van de Meent D., Brown S. C.. Philp R. P. and Simoneit B. R. (1980) Pyrolysis high resolution gas chromatography and pyrolysis high resolution gas chromatography of kerogen and kerogen precursors. Geochim. Cosmochim. .4cta 44~ 999 1013, Yalcin M. N., Welte D, H., Misra K. N., Mandal S. K., Balan K. C., Mehrotra K. L., Lohar B. L., Kumar S. P. and Misra G. S. (1987) 3-D computer aided basin modelling of Cambay Basin, India--a case history of hydrocarbon generation. In Petroleum Geochemistry and Exploration in the Afro-Asian Region (Edited by Kumar R K., Dwivedi P., Banerjie V. and Gupta V.), pp. 417~450. Balkema, Rotterdam. Zhiwet S. and Xiuli G. E. (1987) The generation of hydrocarbons by kerogen thermal simulation. Energy Sources 9, [++15,