Abstract
Hydrocarbon production in the Michigan basin occurs primarily from Silurian pinnacle reefs or Middle Ordovician and Middle Devonian linear, faulted, and dolomitized structures. The writer has previously proposed a wrenching model for the basin based on lineament (fault) patterns from Landsat imagery and outcrop fracture analyses (“ground truth”). The azimuths of existing linear producing fields, whether from Trenton-Black River or younger rocks, closely fit the shear model.
Analyses (x-ray diffraction) of numerous well samples from several producing fields show dolomite/calcite ratios of epigenetically formed dolomite (porous reservoir rock) channelways along vertical shear faults, shear folds, cross faults, cross folds, and stratigraphic permeable offshoots from the fault channelways of the wrenching model. The dolomitizing fluids probably entered the fault channelways from artesian waters from below. If so, basin form would be important to reservoir rock development in this system.
Geophysical exploration for the strike-slip shear faults in nearly horizontal rocks generally has proved elusive, even for accompanying shear folds where they have small amplitudes. The Trenton-Black River Albion-Scipio giant field is shear faulted but not shear folded. Geophysical search for other similar structures has been far from successful.
Thus, “model fitting” in many instances may be the most effective tool. It should be recognized that faults sensed by the reflected infrared of Landsat are open systems, at least near the surface. It is the “unseen” closed system components of the model for which one searches.
