Regional mapping and qualitative petroleum resource assessment of the Magdalen Basin, Gulf of St. Lawrence, Quebec, Prince Edward Island, New Brunswick, Nova Scotia, and Newfoundland and Labrador

Abstract

The Geological Survey of Canada conducted a broad regional study of the Magdalen Basin in the Gulf of St. Lawrence, as part of the Marine Conservation Targets initiative. MCT is a national initiative to protect more of Canada's offshore areas, and resource assessment and related regional mapping are part of the review process. This study assembled a large seismic and geologic database that allowed new regional mapping of several key horizons in this basin. Digital seismic data was donated by industry, and reprocessing undertaken both in-house and with contractors. Wells were correlated and tops from literature were used to indentify regional reflection packages. Regionally consistent two-way time interpretations add to confidence. Depth conversion used regional time-depth functions from literature, which were developed from refraction data, with a residual correction for the water column. Nine regional depth maps and eight isopach maps were produced, including Pre-Horton Basement, Horton Group Isopach, Base Windsor Group, Top Salt, Top Bradelle Formation, Bradelle / Cumberland Isopach, and Top Cable Head Formation. These maps illustrate that the Pre-Horton basement is about 15 km deep in the centre of the basin. Two main trends are visible in the Horton Grabens, which may relate to basin formation, and no significant reactivation of deeper Appalachian structure is observed. In the basin centre, the more robust Base Windsor Unconformity horizon reaches about 12 km deep, and a key reservoir and source sequence in the Bradelle Formation reaches 7 km. These maps are useful for considering regional stratigraphy. The new mapping also constrained basin models and became the input for our Qualitative Petroleum Potential map. Basin modelling reveals scenarios where oil may be preserved. The petroleum potential of the region is highest north of Îles de la Madeleine and southeast of Îles de la Madeleine and northwest of Cape Breton.