Upper Ordovician Organic-Rich Mudstones of Southern Ontario

Abstract

Despite unconventional hydrocarbon exploration activity in Upper Ordovician mudstones of adjacent jurisdictions, these units are not well characterized in Ontario. The Ordovician shale sequence studied for this project consists of the Georgian Bay Formation, the Blue Mountain Formation and its Rouge River Member and the Collingwood Member of the Cobourg Formation, from top to bottom. In 2011, the Ontario Geological Survey drilled a 496.5m deep well in Wellington County, to collect core samples through the Upper Ordovician shale sequence. Samples were analyzed for gas concentration and composition, methane isotope composition, adsorption isotherms, rock mechanics, Rock-Eval® 6 pyrolysis, mineralogy, permeability, porosity and gas, oil and water saturations. The well was also logged geophysically. The interval with the best source rock potential consists of the Rouge River and Collingwood members. In the Wellington well, these members are 13.7m and 10.4m thick, respectively. A thin phosphatic bed is present between the two units. The Rouge River Mb is a highly fissile dark bluish-grey to black, non-calcareous shale, whereas the Collingwood Mb is a dark brown to black, fissile, impure limestone, with very thin bioclastic interbeds. An oil stain was observed near the top of the Collingwood Mb in this core. Results confirm that the Rouge River and Collingwood members represent the most organic-rich interval (up to 4.68 wt%). Rock-Eval® 6 pyrolysis Tmax data (438°C to 442°C) from these units suggests temperatures in the early oil window. Methane isotopes indicate a thermogenic source. The Rouge River Mb has high oil saturation (up to 31.5%) and a mix of type II/III kerogen (HI between 280 and 419) while the Collingwood Mb shows high gas saturation (77.2%) and a type II kerogen (HI between 532 and 650). The Rouge River and Collingwood members present different characteristics for almost all geochemical and geophysical parameters. This project also studied the Ordovician shale sequence across southern Ontario to better define the extent and thickness of these units. Drill core and cuttings were collected from previously drilled wells and analyzed for mineralogy by X-Ray diffraction and Rock-Eval® 6 pyrolysis. However, to efficiently portray the regional potential of these units as source rocks, additional new core and gas samples should be collected and analyzed for crucial parameters, like porosity, permeability and gas/oil concentrations, compositions and saturations amongst others.

AAPG Datapages/Search and Discovery Article #90195 © 2014 Eastern Section Meeting, London, Ontario, Canada, September 27-30, 2014