Lower Paleozoic Shale Gas and Shale Oil Potential in Eastern Canada: Geological Settings and Characteristics of the Upper Ordovician Basin
The Upper Ordovician Utica Shale (50 to 300 m thick) and Macasty Shale (40 to 100 m thick) are found in southern Quebec and Anticosti Island, respectively. Over the years, these two units have been studied for their hydrocarbon source rock potential. The Utica and Macasty calcareous 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 deep marine, poorly oxygenated 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 in a larger scale eustatic sea level fall in Late Ordovician. 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 almost entirely in the gas window whereas the Macasty Shale (TOC up to 5%) in Anticosti Island straddles the oil and gas windows. Understanding of mineralogical variations and mapping of TOC and HI domains are available for the Utica although this level of detail is currently not available for the Macasty.
Exploration in the Utica Shale in southern Quebec started in 2007 and has demonstrated potential for yielding significant volume of natural gas after multistage fracturing. Pre-commercial production pilot projects are in the planning stage. Preliminary geological data indicate that the Macasty Shale could represent a shale oil target in Anticosti Island.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California