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ABSTRACT: Reservoir Geology of the Dundee Limestone (Devonian), West Branch Field, Michigan

Brendan C. Curran, Neil F. Hurley

West Branch field occurs near the center of the Michigan basin as a low relief, northwest-southeast-trending anticline. Since 1934, the Dundee Limestone (Devonian) has produced over 12 million bbl of oil from this field. Sediments of the Dundee were deposited on a carbonate ramp that dipped northwest. Core studies show that depositional facies are dominated by a normal-marine, peloid-bioclastic carbonate sand. A coarse-grained crinoid grainstone, deeper in the section at the northwest end of the field, represents quiet water deposition in an extensive crinoid meadow. Field-wide, the top 10 to 50 ft of the Dundee consist of micritic carbonates with restricted fossil assemblage. The top of the Dundee is a disconformity that appears to be a pyritized, extensively bioeroded h rdground.

Trace amounts of dolomite are common throughout the field. However, pervasive dolomite is common only in the top 10 to 15 ft of the Dundee. This dolomite has generally high porosity (5 to 15%), but very low permeability (0.1 to 1.0 md). Most reservoir porosity is in limestone and is of a primary interparticle nature. Previous workers have concluded that porosity and permeability in this field are controlled by fracture-related dolomite. This study concludes that fracture-controlled dolomite is not important, and that porosity and permeability in the Dundee are controlled by depositional facies that have largely retained primary porosity and permeability.

AAPG Search and Discovery Article #90998 AAPG Eastern Section Meeting, London, Ontario, Canada, September 10-12, 1990