Credit: Photographic Services, Shell International Limited

5. Source Rocks

Within the onshore Maritimes Basin, known and potential source rocks exist in rocks ranging from Early Devonian to Late Pennsylvanian age, and believed to extend into the adjacent offshore regions (Table 5.1). While extensive studies were completed in the former, the small number of wells (11), depth of penetration, and sampling issues together constrains confidence in their characteristics and extent therein. There have been a number of studies and analyses on potential source rocks.  As related to the Sydney Basin, Mukhopadhyay (2004) and most recently Fowler and Webb (2017) provide excellent overviews, compilations, and new analyses of the source rocks in Cape Breton Island’s onshore and offshore basins.

There are only three wells in the offshore potion of the Sydney Basin, two of which are in very close proximity to each other. None penetrated the known rich oil- and gas-prone Horton Group lacustrine successions nor confirmed the presence of younger Windsor (restricted marine) and Mabou (lacustrine) potential source intervals. Evidence reveals the presence of some organic-rich rocks in shallower sediments. Tables 5.2 to 5.8 are compilations of geochemical analyses by group and formations for all five wells in the Sydney Basin. Note that not all wells are included in each table. This is because either well did not penetrate the respective formation, and/or no analyses were performed (e.g. CCS-NS No.1). For the two North Sydney wells, kerogen type was not defined in their tabulated analyses, but was identified as type III based on descriptions and commentaries in the reports. The coarse sampling procedures (decametres) limits the identification, physical characteristics and analysis of organic-rich intervals or beds. Electric logs have also not identified such intervals. Nevertheless, useful information on the sections penetrated and their potential does exist.