Hydrothermal Dolomite Reservoirs (HTDR) in a Mature Petroleum Province, Michigan Basin, U.S.A.

David A. Barnes, G. Michael Grammer, William Harrison, and Robb Gillespie
Western Michigan University, Kalamazoo, MI

Carbonate reservoirs with a strong overprint of fracture related hydrothermal dolomite (HTDR) have unique spatial distribution, internal geometry, and hydrocarbon production characteristics. Recognition of HTDR in mature but under-studied basins has important commercial implication. Improved reservoir characterization and enhanced recovery operations and support for untested exploration concepts can result from identification of HTDR. One of the first well-documented examples of HTDR in a giant oil field is the Trenton/Black River (T/BR), Albion-Scipio field in the Michigan basin, USA. Wrench faulting and Riedel shear related features, including dilational fractures, and primary facies controlled fluid flow conduits are considered fundamental to the origin of HTDR relative to regional limestone in Albion-Scipio.

Sedimentologic and petrologic analysis of several producing formations in core including T/BR, Ordovician St. Peter Sandstone (aka “PdC”), and Devonian Dundee Formation throughout the Michigan basin indicates a pervasive overprint of hydrothermal dolomite. Hydrothermal mineralization is also observed in units in the basin as young as Mississippian/Pennsylvanian age. Structural mapping and log analysis in the T/BR and Dundee suggest close spatial relationship among gross dolomite distribution and interpreted, wrench fault-related NW-SE and NE-SW structural trends. Hydrothermal origin of much dolomite in several stratigraphic intervals, from Ordovician through Mississipian/Pennsylvanian age and persistent association of this dolomite in reservoirs coincident with wrench fault-related features is strong evidence in support of HTDR in multiple producing intervals in the Michigan basin. Recognition of HTDR in these and other reservoir formations should result in revitalized and improved exploration/exploitation activity and increased production in Michigan and other mature petroleum provinces.