Geochemical characterisation of Middle Devonian oils in NW Alberta, Canada: possible source and maturity effect on pyrrolic nitrogen compounds

Molecular geochemical compositions of a suite of Middle Devonian sourced an d reservoired oils from the Rainbow-Zama-Shekilie sub-basins in N.W. Albert a, Canada, reveal the presence of at least two oil families in the study ar ea. The distribution of each oil family is geographically restricted to a s ingle sub-basin, consistent with the oils being sourced locally within a se ries of closed generation/migration/trapping systems. The diversity in the biomarker distributions of the oils indicates the wide range of depositiona l environments and source materials existing in each sub-basin, rather than mixing of end member oils across different sub-basins. Clear maturity diff erences are observed between the oils from the Rainbow and Zama subbasins. Pre-Cretaceous thermal anomalies along the reactivated regional Precambrian basement faults are proposed as one of the major causes for the relatively high maturity levels for the Middle Devonian source rocks in the study are a. We infer that depositional environment and thermal maturity have had a s trong impact on the geochemical characteristics of the saturated and aromat ic hydrocarbons in the Rainbow-Shekilie-Zama oils, but may not influence th e pyrrolic nitrogen compounds to a significant extent. However, recognition of possible source and maturity effects on pyrrolic nitrogen compounds in other studies suggests that these factors should be considered before the p yrrolic nitrogen compounds are used to characterize petroleum migration. (C ) 1999 Elsevier Science Ltd. All rights reserved.