HYDROCARBON POTENTIAL OF MIDDLE AND UPPER DEVONIAN COALS FROM MELVILLE ISLAND, ARCTIC CANADA

Some of the oldest coals in the world are found within the Middle to Upper Devonian clastic wedge of the Canadian Arctic Archipelago. The coals investigated here occur in the Weatherall, Hecla Bay and Beverley Inlet formations on western Melville Island and range in age from Late Givetian to Middle Frasnian. Many of these coals are rich in liptinite macerals, particularly sporinite and hence can be termed cannel coals. Both elemental and Rock-Eval analysis indicate these coals have the potential to generate liquid hydrocarbons. A good correlation between % liptinite with both H/C or Hydrogen Index is observed up to about 50% liptinite after which the latter two parameters level off. The coals range in maturity from 0.61 to 0.87% R(o) and hence should be in the oil window. The amounts of hydrocarbons that can be extracted from the coals when expressed in mg/g organic carbon are very low, suggesting that they are poor source rocks for oil. All the extracts except for the most mature and vitrinite-rich sample show high pr/ph ratios and biomodal n-alkane distributions. A cannel coal from The Beverley Inlet Formation has a very unusual triterpane distribution that includes regular, AB-ring desmethyl and AB-ring methyl hopanes. Steranes are in very low concentrations compared to hopanes in all samples. The relative abundance of C28 and C29 steranes appears to be influenced by maceral composition. Hydrous pyrolysis at 330-degrees-C for 72 h generated greater amounts of hydrocarbons from the coals suggesting they could be the source of liquid hydrocarbons at greater maturities. The hydrous pyrolysis experiments also indicate that thin-walled spores are more reactive than thick-walled spores at lower temperatures. The coals on Melville Island are not thought to be significant source rocks for the oil and gas occurrences in this area of the Canadian Arctic because they make up only a very small fraction of the total sedimentary package.