Petroleum Systems of the Scotian Basin

Abstract

The Scotian Basin extends over an area of ∼260,000 km² in the Atlantic, offshore Nova Scotia, eastern Canada. It is a classic, passive volcanic conjugate margin containing up to 15 km of Mesozoic-Cenozoic sediments. There have been 127 exploration wells drilled since 1967 as well as 78 development wells. To date, there has been 25 discoveries, mostly in the Sable Island area, but only one has been made since 1986. Production of light oil from the Cohasset-Panuke fields has occurred since 1993 and gas from the giant Venture and surrounding fields since 1999. Starting in 2008, the Offshore Energy Research Association of Nova Scotia (OERA) financed a Play Fairway Analysis Program in order to stimulate renewed exploration which included a series of studies of petroleum systems studies. This presentation use the results from these studies as well as data from on-going analyses and some older Geological Survey of Canada unpublished reports to provide an updated understanding of the area. Mostly gas discoveries with minor amounts of condensate/light oil have been made on the Scotian Shelf. Determining the source of these hydrocarbons has been difficult because accumulations are dominated by light hydrocarbons with very low concentration of biomarkers. Additionally rock samples in many wells have been compromised by drilling practices. Rock-Eval/TOC data indicates that the most significant source rocks are Tithonian deltaic (‘Verrill Canyon’) shales containing Type III-II organic matter. The characteristics of hydrocarbons agree with those expected from this interval although there is still not an unequivocal oil-source rock correlation. There is a possibility of contributions from other Late Jurassic and Early Cretaceous shales, but, to date, there is no strong evidence for a contribution from a more oil-prone Lower Jurassic source rock. Evidence from the conjugate margin, offshore Morocco, suggests that this could be a possibility on the deep water Slope. Some geochemical data (e.g. gasoline range hydrocarbons, carbon isotopes) suggests that it is possible to split Scotian Shelf light oils into sub families that likely reflect regional variations in the Tithonian source rock. Based on some previously reported data from the Annapolis G-24 well and initial results from the 2015 piston coring cruise, thermogenic hydrocarbons, as represented by wet gas, are present on the deep water Scotian Slope. The source of these hydrocarbons remains undetermined.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016