Oil Field Structural Mapping and the Distribution of Dolomite in the Dundee Formation in Michigan

Barnes, David A., Grammer, G. Michael, Harrison, William B. III, Gillespie, Robb, Stewart, Joshua, Wahr, Amanda, and Kirshner, Joshua

Department of Geosciences, Western Michigan University, Kalamazoo, MI 49008

The Dundee Formation of the Michigan Basin has produced over 350 million barrels of oil since the late 1920’s. About half of the 100 fields produce from dolomite, however the origin of dolomite is unclear from the existing literature. A new research project, partly funded by the U.S. Department of Energy, is currently underway at Western Michigan University to determine the origin and distribution of dolomite in the Dundee and two other prolific carbonate reservoirs in Michigan. The objective of the project is to identify mechanisms for dolomite genesis, especially as related to hydrocarbon reservoir geometry and rock properties. Petrographic, isotopic, and fluid inclusion analyses of core and sample material will further refine the interpreted origin of dolomite.

The Dundee in the central Michigan is divided into an upper “Rogers City” and a lower “Reed City” interval. The “Rogers City” is an open shelf wackestone that has minimal primary porosity and permeability. The “Rogers City” has satisfactory reservoir quality only when fractured and pervasively dolomitized. The “Reed City” contains significant primary porosity and permeability in shallow shelf skeletal grainstones and boundstones. “Reed City” reservoirs are mostly present in limestone parts of the formation although important reservoir intervals also exist in dolomitized areas.

Application of digital structural mapping techniques and lithologic analyses of digital wireline log data provides insight into the origin of the dolomite. Lateral and stratigraphic extent of dolomite in many central basin Dundee fields is closely related to oil field scale structures interpreted as faulted, asymmetrical anticlines and/or high density, small-scale faults lower on structures. Direct spatial correlation between intensity of dolomitization and these interpreted fault features supports a fracture-related, probable hydrothermal component to dolomitization in many, central Michigan basin Dundee fields.