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Large oil pools and coal beds are occasionally found associated within the same sedimentary series, but mostly in tertiary basins. For some of these series it has been demonstrated that the oil originated, at least partly, in the coal beds. This is probably true for more of them, although it was not demonstrated, given the lack of geochemical studies.
In Paleozoic series, which account for most coals, at least in Europe, association of oil pools and coal beds is very rare. Moreover the oil pools are small. However, gas pools originating in coal beds have been found, and some are very large.
Pyrolysis studies indicate that most coals, whatever their ages, have a variable but often fair capacity to produce oil in geologic situations. However, for Paleozoic coals, as for many other Paleozoic kerogen bearing sediments, complex geologic history resulted in migration dissipating the generated oil. In some favorable situations, reburial in post-Paleozoic times produced gas, and the presence of very efficient seals (salt) allowed gas pools to form.
Furthermore, petrographic examination shows the exinite content should not be taken as a measure of oil potential, because a large part of this potential lies in macerals which are classified presently in the vitrinite group.
Careful use of the methods of petroleum geochemistry will increase the chances of finding oil pools in Paleozoic coal measures of Europe.
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