THE PETROLEUM POTENTIAL OF SOME TERTIARY LIGNITES FROM NORTHERN GREECE AS DETERMINED USING PYROLYSIS AND ORGANIC PETROLOGICAL TECHNIQUES

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 S1/S1 + S2 ratio, it gives a high yield on solvent extraction during which a significant fraction of the S2 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.