Reservoir Compartments in Albion-Scipio and Stoney Point Fields: Unique Geologic Model for Unique Reservoirs

Dennis R. Swager, Neil F. Hurley

Located near the southern margin of the Michigan basin, Albion-Scipio and Stoney Point fields have produced more than 125 million bbl of oil from dolomites in the Middle Ordovician Trenton and Black River Groups. Albion-Scipio is 30 mi long and Stoney Point is 10 mi long and both fields are about 0.5 mi wide. The dolomites of these linear producing trends are in abrupt lateral contact with adjacent non-productive regional limestones.

Significant vertical and areal heterogeneities within these reservoirs seem to be associated with nearly vertical natural fractures that are commonly recognized in core descriptions and open-hole logs. Although core porosities range only from 0 to 12%, core permeabilities range over six orders of magnitude from 0.01 to 8,000 md.

The proposed geologic model assumes that porosity development is directly and genetically related to natural fracturing. In the model, these dolomitized rocks are broken into narrow, elongate reservoir compartments oriented parallel with local structural features. These compartments are linear blocklike splinters of well developed porosity and permeability, and are separated by nonreservoir dolomites that act as effective barriers to lateral fluid flow.

Recent drilling of nearly horizontal boreholes in Albion-Scipio field not only supports this model but provides an average width of less than 50 ft for individual reservoir compartments. Bottom-hole pressure data and production characteristics also support this compartmental model that helps to explain the heterogeneous nature of these oil fields.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.