Hydrocarbon Resources in the Upper Ordovician Black Shales in Quebec (Eastern Canada): from Gas / Condensate in the Utica to Oil in the the Macasty

Lavoie, Denis; Thériault, Robert; Sejourne, Stephan; Lefebvre, René; Mallet, Xavier

In Eastern North America, a 50 - 300 m-thick regional blanket of Upper Ordovician organic matter-rich limy shales extends for over 2500 km, from Ohio to western Newfoundland. The succession is known as the Utica (Ohio, New York, southern Quebec) and the Macasty (eastern Quebec) Shale. Regionally, the thermal maturation of the shales is highly variable, going from dry gas to oil windows and is controlled by a complex burial history involving Taconian, Acadian and Alleghenian tectonic wedges.

The Upper Ordovician Utica Shale (50 to 300 m thick) and Macasty Shale (50 to 100 m thick) are found in southern Quebec and Anticosti Island, respectively. The Utica and Macasty limy shales overly the Ordovician carbonate foreland platform; the calcareous shales started to accumulate when, because of rapid increase of relative sea level rise, the backstepping carbonate producing zone was partially shutdown leaving siliciclastic muds with subordinate carbonate mud to accumulate in an interpreted poorly oxygenated marine setting. Largely unknown basin configuration resulted in variation in thickness and lateral character of the sedimentary accumulations whereas the variations in the vertical succession resulted from yet to demonstrate, higher frequency sea-level fluctuations. Both shales have been deformed during the Late Ordovician Taconian Orogeny although if the degree of deformation was relatively minor, it increases significantly with structural thickening in the Appalachian domain. Previous works on the source rock potential of the Utica and Macasty shales has led to a regional understanding of the distribution of thermal domains. The Utica Shale (TOC up to 3%) in southern Quebec is in the oil/wet gas domain at the northeastern end of the exposed Ordovician platform although for most of this geological domain, the Utica is within the dry gas zone. The Macasty Shale (TOC up to 5%) in Anticosti Island straddles the oil and wet gas windows. Twenty-three shale gas exploration wells have been drilled since 2007 in the Utica Shale resulting in the successful production testing of significant volume of natural gas after multistage fracturing. Current best estimates indicate original gas-in-place values between 120 and 140 Tcf. Historical geological data and recent core analyses indicate that the Macasty Shale could represent a shale oil target in Anticosti Island and current best estimates suggest original oil-in-place values of about 45 BBO.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013