Shale Gas Potential for the Ordovician Shale Succession of Southern Ontario
Catherine Béland Otis
Ontario Geological Survey, Sudbury, ON, [email protected]
In 2011, the Ontario Geological Survey (OGS) conducted a drilling program to assess shale gas potential for the Ordovician shale succession present in Southern Ontario. One well was cored to a depth of 496.5 m (~1629 ft) and samples were collected and analysed for gas desorption, adsorption isotherms, gas composition, methane gas isotopic composition, mineralogy, total organic content, Rock-Eval6 pyrolysis, porosity, permeability, water and hydrocarbon saturations and rock mechanics. At this time, not all data has been received by the OGS. Also, the well was geophysically logged for gamma-ray, neutron, porosity, density, sonic and induction.
The Ordovician shale succession includes, in descending order, the Queenston, Georgian Bay and Blue Mountain formations, and the Collingwood Member of the Cobourg Formation. The Queenston Formation will not be considered here. The Georgian Bay Formation consists of about 89 meters (292 ft) of greyish to bluish shale and limestone. The Blue Mountain Formation consists of 2 parts: an upper 68 m (223 ft) thick unit characterized by blue-grey shales with some minor limestone beds; and a lower unit, called the Rouge River Member, which consists of 15 meters (49 ft) of organic-rich black shales. The contact of the Blue Mountain Formation with the underlying Collingwood Member is characterized by a phosphatic bed a few centimetres thick. The Collingwood Member consists of 8 meters (26 ft) of dark grey to black organic-rich calcareous lime mudstone.
The Georgian Bay and upper Blue Mountain formations, with organic content less than 1 wt%, have the highest porosity values (7.66 %), probably associated with limestone beds, whereas gas desorption values do not exceed 8.6 scf/ton. However, the Rouge River and Collingwood members, characterized by high total organic content (≤ 4.55 wt %) have the greatest gas desorption values (>15 scf/ton). Furthermore, oil saturation within the Rouge River Member reaches 31.5%, while the Collingwood gas saturation is 77.2%. Gas composition is characterized by concentrations of methane from 83.6% to 94.6 %, of ethane from 3.7% to 7.9% and of propane and heavier hydrocarbons from 1.5% to 5.8%. Methane isotopic composition includes δ¹³CC1 values ranging from -38.9‰ to -25.7‰ and δDC1 values from -213.5‰ to -188.0‰.
Future work by the OGS includes a regional study of the Ordovician shale succession to evaluate the units’ extent and to establish their stratigraphic equivalents in adjacent jurisdictions, if any. Geology, organic content, Rock-Eval6 pyrolysis and mineralogy profiles will be produced for about 12 wells located throughout Southern Ontario.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012