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Hydrothermal Dolomite Reservoir Facies (HTDRF) in the Dundee Limestone, Central Michigan Basin, USA

D. A. Barnes and W. B. Harrison III
Western Michigan University, Kalamazoo, MI ([email protected])

HTDRF is a distinctive carbonate reservoir type that contains major oil and gas reserves worldwide. A well-documented and highly productive example of HTDRF in Michigan occurs in Ordovician rocks of the Albion-Scipio and Stoney Point Fields. The major geological features in common, globally, in the HTDRF are: 1) extensive diagenetic modification of the reservoir rock matrix to a distinct suite of alteration minerals (saddle dolomite andMVT-like mineralization) through hydrothermal processes, and 2) genetic association of HTDRF with complex fault/fracture systems attributed to reactivated, transcurrent basement faults.

Initial petrologic observations, oil field structural mapping, and production characteristics in several Dundee oil fields suggest that HTDRF are important in the west-central Michigan basin. Saddle (hydrothermal) dolomite is a common vug and fracture fill in association with highly fractured, pervasively dolomitized rock matrix. The irregular top of Dundee porosity (top dolomite) structure in the Vernon Field (Isabella CO., MI) for example, is interpreted as the expression of extensive NW-SE, en-echelon, sinistral Riedel shear fractures/faults. These faults and related fractures, some with large vertical extent, were probably fluid flow conduits for dolomizing fluids and hydrocarbon migration on a geological time scale, and are conduits for formation fluid flow (including water) on a production time scale.

Very high initial oil production (thousands to tens of thousands of BOPD in some wells) in strong bottom water drive Dundee dolomite fields was typically associated with rapid oil production decline and increase in water production. These fields probably posses dual porosity systems (generally low matrix porosity with high fracture density) that should have major impacts on production characteristics and dictate effective drilling and completion procedures. Careful reservoir characterization, in the context of generic HTDRF properties, should provide guidance in interpreting unusual geological features and formulating exploration, production, and enhanced recovery programs in central basin Dundee fractured dolomite reservoirs.

AAPG Search and Discovery Article #90900©2001 AAPG Eastern Section Meeting, Kalamazoo, Michigan