ABSTRACT

Oil seeps have been known to occur in the Devonian carbonates and clastics in the eastern Gaspé for over a hundred years. They are situated on tight anticlines and are often associated with fractures along fault zones. Most of the wells drilled in the region have encountered oil or gas shows. These oils are grouped into paraffinic (43-47° API), and intermediate (27-30° API) types, the former being amber to red in colour and the latter, dark green to brownish black.

Previous studies have demonstrated the presence of hydrocarbon source rocks in the Lower Devonian Cap Bon Ami and Grande Grevè Formations. Mass spectrometry and Gas-Solid-Chromatography analyses, undertaken on an oil sample recovered from the overlying Lower Devonian York River Formation, and on two source-rock extracts from the Grande Grevè and Cap Bon Ami Formations, show that the oil is relatively rich in alkanes but has a similar naphthenic content to that of the rock extracts. It also contains thiophenic aromatic compounds present in the Cap Bon Ami extract.

A Lower Devonian source may be suggested for the oil show on the basis of the above resemblance.

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