Robb Gillespie ([email protected] 269-387-8633), David A. Barnes, G. Michael Grammer, and William B. Harrison, Michigan Geological Repository for Research and Education (MGRRE), Western Michigan University, Kalamazoo, MI

Michigan’s only giant oil field, the Albion/Scipio Field, has produced over 125 million barrels of oil and is used as an analog for much of the Trenton-Black River exploration in Eastern North America. Current reservoir models, based on published literature suggest extensive fracturing and brecciation followed by pervasive hydrothermal dolomitization created the field’s reservoir architecture. The general impression of this reservoir is one of facies-independent and fabric-destructive processes, especially dolomitization that created the reservoir quality.

Detailed examination of numerous cores from the field and a few outside the field, do show some intervals of extensive fracturing and brecciation along with hydrothermal (saddle) dolomite cement. Many other cores show only limited fracturing and rare saddle dolomite cement. Some of the cores, in the heart of the field, show almost no fracturing although much of the cored interval is dolomitized. Several well cores show interbedded dolomite and limestone with primary facies fabrics and textures very well preserved in both lithologies. Depositional environments can easily be interpreted from most of the core material. These cores show a diverse set of shallow shelf and peritidal facies stacked in multiple cycles through the Black River and Trenton intervals.

It appears from this core study that fracturing and brecciation is very laterally restricted to the proximity of major faults within the field. Wells a short distance from these faults may show little or no fracturing. Dolomitization does, however, extend well beyond the fractured zone. Primary sediment texture and porosity may have provided sufficient fluid pathway to transmit the dolomitizing fluids substantial distance from the major faults.

AAPG Search and Discovery Article #90059©2006 AAPG Eastern Section Meeting, Buffalo, New York