ABSTRACT: Cambrian Oil and Gas Reservoirs of Southwestern Ontario

TREVAIL, ROBERT A., Orion Resources Consulting, Ltd., London, ON, Canada

Upper Cambrian rocks underlie almost 48,000 km2 of southwestern Ontario and are a remnant of a once extensive orthoquartzite-carbonate suite of rocks deposited during initial encroachment of Paleozoic seas onto the North American craton. They are characterized by exceptionally mature sandstones, shallow water carbonates, and a lack of shale. Rock types, sedimentary features (bedding characteristics, burrowing, etc.), and lithologic associations indicate that deposition occurred in predominately high energy, shallow water environments (fluvial to shallow shelf).

Porosity is distributed unevenly throughout the entire stratigraphic interval with primary interparticle pore space being the most common. Secondary porosity types include intraparticle following dissolution of feldspars, oomoldic, and intercrystalline. Quartz and feldspar overgrowths, carbonate cements (microcrystalline dolomite and blocky ferroan calcite), and anhydrite tend to reduce available pore space.

Reservoir trapping mechanisms include stratigraphic traps along a pinch-out edge, structural traps associated with faulting, and a combination of pinch-out edge and faulting. Regional geological mapping, high resolution aeromagnetic (HRAM) and gravity surveys, and conventional 2D seismic are used as exploration and development tools.

Four commercial Cambrian reservoirs have been discovered in Ontario to date. The Gobles, Clearville, and Willey pools each have recoverable oil reserves of between 250,000 and 260,000 m³ (1.57 and 1.63 million bbls). Step-out drilling around the Innerkip pool during the period 1990 to present resulted in the discovery of additional gas reserves with cumulative production to date exceeding 600,000 103m³ (21.3 bcf). Other non-commercial gas pools include New Glasgow, Rockton, Electric, and St. Patricks.

Search and Discovery Article #90907©2000 AAPG Eastern Section Meeting, London, Ontario, Canada