Hydrocarbon exploration in Québec: why look to the marine environment?
Mathieu J. Duchesne, Nicolas Pinet, Denis Lavoie, Andrée Bolduc (GSC-Q) and D. Calvin Campbell (GSC-A)

Hydrocarbon exploration in Québec has experienced an upsurge in activity these past few years, spurred on by discoveries in adjacent sedimentary basins with comparable geological settings to the basins of Québec. Until now, recent exploration efforts have taken place onshore, within the Appalachians and the St. Lawrence Platform. The latter geological environment hosts world-class oil and gas fields in neighbouring New York and Ontario regions, and its potential in southern Québec is beginning to be better defined. In contrast, the offshore parts of the platform remain poorly known. Historically, the lack of interest for marine exploration in Québec can be partly explained by the poor quality of available geophysical data. Moreover, the high cost of exploration work at sea, maritime jurisdiction problems, and the complexity of environmental assessment procedures have hindered prospecting in the marine extension of this geological environment. Nevertheless, several geological arguments can be made to raise interest about the potential of the marine environment.

The Geological Survey of Canada and its partners have led various research projects in offshore regions of Québec to compensate for gaps in the geological knowledge base for the offshore environment, and to assess its hydrocarbon potential. So far, the submarine extension of the platform has been delineated and subdivided into a largely monoclinal zone (comprising younger rocks than those that outcrop on Anticosti), and a zone characterized by large open folds. Recent modeling of potential field data suggests the Taconian deformation front between Anticosti and Gaspésie lies further north than was generally believed.

The St. Lawrence Estuary is characterized by a number of vents, some of which are active and include carbonate crusts. These vents are preferentially rooted in the Paleozoic platform, suggesting that the gas is of thermogenic origin derived from open reservoirs in the platform. These vents reveal that the petroleum system is operational and that a source of mature hydrocarbons is present. The vents are very abundant in the upstream part of the estuary, but practically absent in the Honguedo Strait where an impermeable sediment cover (post-Lower Silurian) may be present. And finally, the presence of gas within Quaternary sediments suggests the existence of reservoirs, the thickness and lateral extent of which are still poorly constrained.