ABSTRACT: Depositional and Diagenetic Controls on Ordovician Trenton and Black River Group (Reservoirs), Southwestern Ontario

COLQUHOUN, Steven A., Telesis Petroleums Inc., London, Ontario, Canada, and ALLAN R. PHILLIPS, Kerr-McGee Canada Ltd., Calgary, Alberta, Canada

Fracture-controlled dolomite reservoirs of Ordovician (Caradocian) age occur in the Michigan basin and have provided exploration targets within southwestern Ontario and Michigan since the early 1900s. Over 160 million barrels of oil have been produced from elongate linear reservoirs in the Trenton and Black River groups on the southeastern margin of the Michigan basin. A 250 m sequence of crinoidal grainstone, packstones, and mudstones were deposited on an extensive crinoidal shoal ramp. Paleozoic fault and fracture systems within the Michigan and Applachian basins are the conduits for basinal dolomitizing hydrothermal solutions that diagenetically altered the regional limestone sequence to porous, permeable dolomite reservoirs. The extent of dolomitization is variable and also a func ion of original depositional fabric, fracture intensity; and thicklaess of underlying Cambrian-Ordovician clastic and carbonate sequence.

The coarser grained, cleaner dolomitic grainstone units form the bulk of the storage capacity in this reservoir while the finer grained dolomitic mudstones, wackestones, and packstones are essentially nonreservoirs. An extensive fracture network with associated solution enlarged cavernous porosity occurs within all facies and impart enhanced permeabilities and deliverability to these reservoirs.

These regionally heterogeneous linear, narrow, dolomite reservoirs continue to be an active exploration target in southwestern Ontario and elsewhere in the Michigan and Appalachian basins.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)