Org. Geochem. Vol. 17, No. 6, pp. 805-826, 1991 0146-6380/91 $3.00+ 0.00 Printed in Great Britain Pergamon Press plc The petroleum potential of some Tertiary lignites from northern Greece as determined using pyrolysis and organic petrological techniques* MARTIN G. FOWLER, 1 THOMASGENTZIS, 2 FARIBORZGOODARZI l and ANTHONYE. FOSCOLOS 3 qnstitute of Sedimentary and Petroleum Geology, Geological Survey of Canada, 3303-33rd St N.W., Calgary, Alberta, Canada T2L 2A7 2Coal Research Centre, Alberta Research Council, Devon, Alberta, Canada T0C 1 E0 3Department of Mineral Resources Engineering, Technical University of Crete, 73133 Chania, Greece Abstract---Oil condensate and gas have recently been discovered in the Thermaikos Gulf area of northern Greece. The source of these hydrocarbons is not known, although there is a possibility that more mature equivalents of certain Tertiary brown coals and lignites may be responsible. A contribution from Tertiary terrestrial organic matter to the Epanomi oil is supported by its biomarker distributions, especially the predominance of triterpenoid compounds other than hopanes in the m/z 191 mass fragmentogram. In this study, the hydrocarbon potential of a suite of Greek Tertiary lignites is first examined using Rock-Eval analysis. Three samples are then further investigated using organic petrography, and gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) of the extracted hydrocarbon fractions, as well as by hydrous pyrolysis. An intermontane lignite (6OG-5) contains fluorescing huminite together with resinite. On extraction, this resinite is found to be of predominantly diterpenoid origin. Rock-Eval and hydrous pyrolysis support previous proposals that diterpenoid resinite needs a lower activation energy to generate hydrocarbons than most other types of organic matter. A sample of a lignite deposited in a deltaic environment (MM-3) contains a more diverse collection of liptinite macerals with resinite again predominating. The resinite appears to be mostly of triterpenoid and sesterterpenoid origin. The best hydrocarbon potential is shown by a sample deposited in a lagoonal environment (KAS-3). Little discrete resinite is observed in this sample but it does contain abundant fluorescing huminite. Although it has a low SJSt + $2 ratio, it gives a high yield on solvent extraction during which a significant fraction of the $2 is removed. The fluorescence of the huminite after extraction is greatly reduced. The hydrocarbons of the extract are believed to be predominantly derived from triterpenoid resinite. Unlike the pyrolysates of the other two lignites but in common with the Epanomi oil, the triterpenoids in the KAS-3 pyrolysate are dominated by resin-derived compounds rather than hopanes. This and other similarities between the composition of the pyrolysates of KAS-3 and the oil support the possibility that a more mature equivalent of this lignite could be the source of the Epanomi oil. Key words--Greece, hydrous pyrolysis, lignites, organic petrology, resinite, Rock-Eval INTRODUCTION Oil, condensate and gas discoveries have recently been made in the Thermaikos Gulf area about 30 km southeast of Thessaloniki (Fig. 1). Oil was discovered by the Greek Public Petroleum Corporation at a depth of 2800.5-2838.5 m in Tertiary sediments during the drilling of the Epanomi-2 hole in 1989. Although the actual source rocks are not known, there is a strong suspicion that more mature equivalents of certain Tertiary brown coals could be the source of these hydrocarbons. There have been several reviews that have discussed the possibility that coals can be oil- source rocks (e.g. Durand and Paratte, 1983; Saxby and Shibaoka, 1986; Murchison, 1987; Bertrand, 1989) but few actual proven examples. Low rank coals of Tertiary to Quaternary age are widespread in Greece. Sixty lignite-bearing basins con- taining reserves of 5.3 x 10 9 t of low rank coal have *Geological Survey of Canada No. 28190. been discovered to date (Koukouzas, 1985). Many of these Tertiary coals are relatively rich in liptinite macerals, especially resinite, and contain fluorescing huminite (Cameron et al., 1984; Goodarzi et al., 1990) suggesting the possibility that they could have better hydrocarbon potential than is normally observed for coals. Most lignite deposits in Greece were formed in intermontane basinal settings in graben-fike structures, although some were deposited in near coastal settings such as deltas or alluvial plains (Foscolos et al., 1989). The diversity in the depositional environments is reflected in the suite of samples used in the present study, three of which were selected for more detailed investigations. The 6OG-5 sample comes from Varvoutis Mine in the Florina Basin, northwestern Greece. It is of Lower Pliocene age and was deposited in an inter- montane basin. The MM-3 sample is of Miocene age and was deposited in an estuarine/delta setting near Moschopotamos in the Katerini Basin (Fig. 1). It is the lowermost of three thin coals (about 60 cm thick) 805