Located in the Gulf of St. Lawrence in Quebec, Anticosti Island extends over a length of 220 km and a maximum width of 56 km and covers an area of 7,943 sq-km (3000 sq-mi). Anticosti is a large ESE-WNW oriented structure situated along the Laurentia passive margin of Ordovician carbonates that extends from western Texas to Newfoundland. The geological units forming the island are of Paleozoic age, ranging from the Cambrian to the end of Silurian. The territory, almost unhabited, has large subsurface areas virtually unknown since very few exploration wells were drilled on the island. However, various data accumulated over sixty years now allow us to evaluate the petroleum potential of the region. The current exploration phase recognized the potential of the Middle Ordovician Macasty Shale as a liquid-rich resource play (potential for light oil/condensate production).

The Macasty Shale has properties which compares favorably with other North American shale resource plays and which may be a positive indicator for potential resources initially-in-place. Technical evaluation indicates that the level of organic richness, the thermal maturity, the mineralogy, the formation pressure and temperature, as well the structural features observed thus far in the Macasty in the Deep Macasty Fairway compares favorably with published findings for the oil-rich Utica/Point Pleasant Shale in Ohio and the Eagle Ford Shale in Texas. Resources assessment studies (P50 - Best Estimate) recently published by different groups corroborate the analytical results and the interpretation of the authors concerning the high hydrocarbon potential of the Anticosti Basin. For the Macasty Shale only, current estimations established the potential oil initially in-place (OIIP) to be over 40 billion barrels.

This paper will present how an exhaustive review of vintage data lead to a major update of the oil and gas potential for the entire Anticosti sedimentary basin. Among other things, it will focus on how it is possible, using the knowledge acquired in similar basins, to present a fairly accurate assessment of the petroleum potential for an under-explored sedimentary basin. The methodology presented in this case study can also be seen as a good way to valorize the sedimentary basins where sparse and limited data are the only information available. From a regional perspective, the current assessment of the onshore potential can lay the groundwork for a future evaluation of huge portions of the offshore Anticosti Basin.

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